Steel pipe

What is a steel pipe?

steel pipe is a round steel with a hollow section whose length is much larger than the diameter or circumference. It is divided into round, square, rectangular and special-shaped steel pipes according to the cross-sectional shape; it is divided into carbon steel pipestainless steel pipealloy steel pipe and composite steel pipe according to the material; it is divided into conveying pipe and engineering structure according to its purpose. For thermal equipment, petrochemical industry, machinery manufacturing, geological drilling, steel pipe for high pressure equipment, etc.

steel pipe - Steel pipe

According to the production process is divided into seamless steel pipe and welded steel pipe, which seamless hot steel and cold rolling (pulling) Two kinds of welded steel pipes are divided into straight seam welded steel pipes and spiral welded steel pipes.
Steel pipes are not only used for conveying fluids and powdered solids, exchanging heat energy, making mechanical parts and containers, but also an economic steel. The use of steel pipes for the manufacture of architectural structure grids, pillars, and mechanical supports can reduce weight, save 20 to 40% of metal, and enable industrialized mechanized construction. The use of steel pipes to manufacture road bridges not only saves steel and simplifies construction, but also significantly reduces the area of the protective coating and saves investment and maintenance costs. [1]

Classification of steel pipes
According to the production methods of steel pipes
Steel pipes can be divided into two categories according to the production methods: seamless steel pipes and seamed steel pipes, and seamed steel pipes are referred to as straight seam steel pipes.
1. Seamless steel pipes can be classified according to production methods: hot-rolled seamless pipes, cold-drawn pipes, precision steel pipes, heat-expanded pipes, cold spinning pipes and extruded pipes.
Seamless steel tubes are made of high-quality carbon steel or alloy steel, with hot rolling, cold rolling (pulling).
2. Welded steel pipes are divided into furnaces, electric welding (resistance welding) pipes and automatic arc welding pipes because of their different welding processes. Because of their different welding modes, they are divided into two types: straight seam welded pipe and spiral welded pipe. For the round pipe and shaped (square, flat, etc.) welded pipe.
Welded steel tubes are made by rolling into a tube-shaped steel plate and welded to a seam or spiral seam. In terms of manufacturing methods, they are divided into welded steel pipes for low-pressure fluid transportation, spiral welded steel pipes, direct welded steel tubes, and welded pipes. Seamless steel tubes can be used in various industries such as liquid pressure piping and gas piping. Welded pipes can be used for water pipes, gas pipes, heating pipes, electrical pipes, etc.
According to the material classification of steel pipe
According to the pipe material (steel), the steel pipe can be divided into: carbon pipe and alloy pipe, stainless steel pipe and so on.
Carbon tubes can be divided into ordinary carbon steel tubes and high-quality carbon structural tubes.
Alloy tube can be divided into: low alloy tube, alloy structure tube, high alloy tube, high strength tube. Bearing tube, heat-resistant acid-resistant stainless tube, precision alloy (such as Kovar) tube and high-temperature alloy tube.
According to the classification of steel pipe connection
According to the pipe end connection, the steel pipe can be divided into: light pipe (without pipe end) and wire pipe (with pipe end with thread).
The wire tube is divided into: ordinary wire tube and pipe end thickened wire tube.
Thickened wire tube can also be divided into: external thickening (with external thread), internal thickening (with internal thread) and internal and external thickening (with internal and external threads) and other floor wire tube.
If the wire tube type according to the thread type can also be divided into: ordinary cylindrical or conical thread and special thread and other wire tube.
In addition, according to the needs of users, the wire pipe is generally equipped with a pipe joint delivery.
According to the plating characteristics of steel pipes
According to the surface coating characteristics of steel pipes can be divided into: black (not coated) and coated pipe.
The coating tubes include galvanized tubes, aluminized tubes, chrome-plated tubes, aluminized tubes, and other alloyed steel tubes.
Coating tubes include outer coating tubes, inner coating tubes, and inner and outer coating tubes. Commonly used coatings are plastics, epoxy resins, coal tar epoxy resins, and various types of glass anti-corrosion coating materials. Galvanized pipe is divided into KBG pipe, JDG pipe, threaded pipe and so on.

According to the use of steel pipe classification
1. Pipeline. Such as: water, gas pipe, steam pipe with seamless pipe, oil pipe, oil and gas trunk pipe. Agricultural irrigation taps with pipes and irrigation sprinklers.
2. pipes for thermal equipment. Such as general boiler boiling water pipe, superheated steam pipe, locomotive boiler superheated pipe, smoke pipe, small smoke pipe, arched brick pipe and high temperature and high pressure boiler pipe.
3. The pipe for machinery industry. Such as aeronautical structural pipes (circular pipes, elliptical pipes, flat oval pipes), automotive axle pipes, axle pipes, automobile tractor structural pipes, oil cooler pipes for tractors, square and rectangular pipes for agricultural machinery, pipes for transformers, and bearings pipes and so on.
4. Petroleum geological drilling pipe. Such as: oil drilling pipe, oil drill pipe (for kelly and hexagonal drill pipe), drill collar, petroleum tubing, oil casing and various pipe joints, geological drilling pipe (core pipe, casing, active drill pipe, drill collar , hoop and pin joints, etc.).
5. pipes for the chemical industry. Such as: oil cracking pipe, chemical equipment, heat exchangers and pipelines, stainless acid, high-pressure chemical fertilizers, and transportation of chemical media.
6. The other departments use the pipe. Such as: container pipe (high-pressure gas cylinder pipe and general container pipe), instrumentation equipment, watch shell pipe, injection needle and its medical device pipes. [2]

According to the sectional shape of steel pipe
The steel grades and specifications of steel pipe products are extremely varied, and their performance requirements are also varied. All of these should be differentiated as user requirements or working conditions change. In general, steel pipe products are classified according to the cross-sectional shape, production method, pipe material, connection method, plating characteristics, and use.
According to the cross-sectional shape of the steel pipe can be divided into: round steel pipe and shaped steel pipe.
Special-shaped steel pipe refers to all kinds of non-circular-shaped steel pipe. Among them are: square tube, rectangular tube, oval tube, flat elliptical tube, semicircular tube, hexagonal tube, hexagonal inner tube, unequal hexagonal tube, equilateral triangle tube, pentagonal plum tube, octagonal tube, convex Font tube, double convex tube. Bi-concave tube, multi-concave tube, melon tube, flat tube, diamond tube, star tube, parallelogram tube, ribbed tube, drop tube, inner fin tube, twisted tube, B-tube, D Type tubes and multilayer tubes.
According to the longitudinal section of the steel pipe is divided into: equal section steel pipe and variable section steel pipe. The variable section (or variable section) steel tube refers to a steel tube that undergoes periodic or aperiodic changes along the length of the tube in the cross-sectional shape, inner and outer diameters, and wall thicknesses. The main ones are: outer tapered tube, inner tapered tube, outer stepped tube, inner stepped tube, periodic sectional tube, bellows, spiral tube, steel tube with radiating fins, and barrel with double wire.
Composition inspection of steel pipe
(1) GB3087-2008 “Seamless boilers for low and medium pressure boilers” provisions. The chemical composition test method is based on the relevant parts of GB222-84 and GB223 “Methods for chemical analysis of steel and alloys”.
(2) GB/T5310-2008 “Seamless steel tubes for high pressure boilers” provisions. Chemical composition test method According to GB222-84 and “Chemical analysis method for iron and steel and alloy”, GB223 “Methods for chemical analysis of steel and alloy”.
(3) Inspection of the chemical composition of imported boiler pipes shall be carried out in accordance with the relevant standards stipulated in the contract.

Production methods of steel pipes
Steel pipes are divided into seamless steel pipes and welded steel pipes. In the production process of the seamless steel pipe, the solid pipe or steel ingot is hollowed into hollow cores and then rolled into steel pipes of the desired size. Different piercing and rolling pipe methods are used to form different methods for producing seamless steel pipes. Welded steel pipes are produced by bending pipe blanks (steel plates or steel strips) into pipes and welding the gaps into steel pipes. Due to the different methods of forming and welding used, different methods of producing welded steel pipes are formed.
Seamless steel pipes are mainly produced by hot rolling. The extrusion method is mainly used to produce hard-to-perforate low-plastic high-alloy steel pipes or special-shaped steel pipes and composite metal pipes. Cold-rolling and cold-drawing processes can continue the processing of hot-rolled pipes into small-diameter and thin-wall steel pipes. Welded steel pipe has a simple process, high production efficiency, low cost, and expanding product variety. The main production methods for seamless steel pipes and welded steel pipes are shown in Tables 1 and 2.

Table 1 Seamless steel pipe and welded steel pipe production method
Production Method Basic Procedure Basic Procedure
perforation Rolling tube
Hot rolling Rolling on automatic pipe mills Round billet is perforated in a 2-roll puncher Short headed rolling on a two roll mill with a return roll
Rolling on cycle rolling mills Round steel ingots or tube blanks are perforated in a two-roller puncher;
Square or polygonal steel ingots punched in a hydraulic press
Long Mandrel Rolling on Rolling Mills with Variable Section Holes
Rolling on continuous mill units Round tube blanks are pierced on three- or two-roller punchers;
Continuous casting of billets or square steel ingots in a two-roll pressure punch
Long core rod rolling on 7 to 9 rolling mills;
With tension reducer
Rolling on three-roll mill units Round billet is perforated in a two-roller puncher;
Continuous casting blanks perforated on three-roller punch
Long mandrel rolling on a three-roller oblique mill
Rolling on extension rolling mill units Punching on a 2-roll punch Rolling with long mandrel on a two-roller ramp mill with disc-shaped tension rollers
Rolling on Planetary Tube Mills Cast hollow shell Rolling on planetary mill
Table 2
production method Basic Procedure
perforation Rolling tube
Pipe Jacking Punching a cup-shaped capillary tube on a hydraulic press
On the top of the top machine
Extrusion Pipe blanks are heated and extruded on the extruder
Can continue to roll or pull
Cold rolling Rolling on Cold Rolling Mill with Hot Rolled Pipes
Cold drawing method With hot or cold rolled tube drawing on the cold drawing machine
Furnace welding
Chain furnace welding Heated pipe blanks are molded by welded pipes
Molding while welding
Continuous furnace welding Heated pipe blanks are bent on a roll forming welder
Molding while welding
Welding
Resistance welding Continuous bending on roll forming machines
Welding on electric resistance welding machine
Arc welding Press forming on a press or roll forming on a roll bending machine (straight seam), continuous bending on a forming machine (spiral seam)
Welding on submerged arc automatic pipe welding machine
Inductor welding Continuous bending on roll forming machines
Welding on Inductor Welding Machines


Specifications of steel pipes

(1) Specifications: The specifications of the spiral steel pipe should be listed in the import and export trade contract. It should generally include standard grades (type codes), nominal diameters of steel bars, nominal weights (mass), specified lengths, and tolerance values for the above indicators. China’s standard recommended nominal diameter of 8,10,12,16,20,40mm spiral steel pipe series. The length of supply is divided into two types, length and size. China’s export rebar length selection range of 6 ~ 12m, Japan rebar length range of 3.5 ~ 10m.
(2) Appearance quality: 1 Surface quality. The surface quality of the rebar has been specified in the relevant standards, requiring that the end should be cut straight, with no cracks, scabs and folds on the surface, no harmful defects in use, etc.; 2 Permissible values for dimensional deviation. The requirements for bending and reinforcing bar geometry of rebar are specified in the relevant standards. As stipulated by our country’s standards, the straightness bar steel bending is not more than 6mm/m, and the total bending degree is not more than 0.6% of the total bar length.

Related terms of steel pipe
Size
A. Nominal dimension: It is the nominal dimension specified in the standard. It is the ideal size that the user and the production company hope to obtain. It is also the order size specified in the contract.
B. Actual size: It is the actual size obtained in the production process. The size is often larger or smaller than the nominal size. This phenomenon that is larger or smaller than the nominal size is called deviation.
C. Weight in meters: weight per meter = 0.02466 * wall thickness * (outer diameter – wall thickness)
Deviations and tolerances
A, deviation: In the production process, because the actual size is difficult to achieve the nominal size requirements, that is often more or less than the nominal size, so the standard allows a difference between the actual size and the nominal size. Positive values are called positive deviations, and negative values are called negative deviations.
B. Tolerance: The sum of the absolute values of the positive and negative deviation values specified in the standard is called tolerance, also called “tolerance zone”.
Deviations are directional, ie expressed as “positive” or “negative,” and tolerances are not directional. Therefore, it is wrong to call deviation values “positive tolerances” or “negative tolerances.”
Delivery length
The length of delivery is also called the length of the user’s requirement or the length of the contract. The standard provides the following specifications for the length of delivery:
A, usually length (also known as non-fixed length): Where the length is within the standard length range and no fixed length requirements, are called the normal length. For example, structural pipe standards stipulate that: hot-rolled (extruded, expanded) steel pipes are 3000mm to 12000mm, and cold-drawn (rolled) steel pipes are 2000m to 10500mm.
B. Length of fixed length: The length of the fixed length should be within the normal length range, which is a certain fixed length size required in the contract. However, it is not possible to cut out the absolute length in actual operation. Therefore, the standard defines the allowable positive offset value for the length of the cut length.
The structural standards are:
The cut length of the production length-length pipe is larger than that of the normal length pipe, and the production company’s request for price increase is reasonable. The rate of increase in price varies from company to company, which is generally based on a base price increase of about 10%.
C. Length of doubler: The length of the doubler should be within the normal length range. The length of the doubler and the multiple of the total length should be specified in the contract (for example, 3000mm×3, ie, 3 times of 3000mm, total length is 9000mm). In actual operation, the allowable positive deviation of 20mm shall be added on the basis of the total length, plus the allowance for each single-fold length. Taking the structural pipe as an example, it is specified that the remaining allowance for the cut is: outer diameter ≤ 159mm is 5 to 10mm; outer diameter is 159mm is 10 to 15mm.
If there is no double-length length deviation and cutting allowance specified in the standard, the supply and demand parties shall negotiate and indicate in the contract. The double length is the same as the length of the fixed length, which will greatly reduce the finished product rate. Therefore, the production company proposes a reasonable price increase, and its price increase range is basically the same as the fixed length length.
D. Range length: The length of the range is within the normal length range. When the user requests one of the fixed lengths, it must be specified in the contract.
For example, the length is usually 3000 to 12000 mm, and the length of the range is 6000 to 8000 mm or 8000 to 10000 mm.
Obviously, the length of the range is looser than that of the length scale and the length of the doubler, but it is much more stringent than the usual length, and it also brings a reduction in the finished product rate to the manufacturer. Therefore, it is reasonable for production companies to raise their prices, and the rate of price increase is generally about 4% above the base price.
Uneven wall thickness
The wall thickness of the steel pipe cannot be the same everywhere. There is an unequal wall thickness in the cross-section and the longitudinal pipe body, ie, the wall thickness is uneven. In order to control this non-uniformity, the allowable index of uneven wall thickness is stipulated in some steel pipe standards. The general rule does not exceed 80% of the wall thickness tolerance (executed after consultation between supply and demand sides).
Ovality
In the cross-section of a circular steel tube, there is a phenomenon that the outer diameter is not equal, that is, there is a maximum outer diameter and a minimum outer diameter that are not necessarily mutually perpendicular, and the difference between the largest outer diameter and the smallest outer diameter is an ellipticity (or not). Roundness). In order to control the degree of ellipticity, some steel pipe standards specify the allowable index of ellipticity, which is generally specified as not to exceed 80% of the outer diameter tolerance (performed after consultation by the supply and demand sides).
Curvature
The steel pipe is curved in the length direction, and its degree of curvature is called the degree of curvature. The bending degree specified in the standard is generally divided into the following two types:
A, local curvature: using a one-meter long ruler on the maximum bending of the steel pipe, measure the chord height (mm), which is the local bending value, the unit is mm/m, said the method such as 2.5mm/m . This method also applies to tube end curvature.
B. Full-length total bending: Using a string, pull from both ends of the tube, measure the maximum chord height (mm) at the bend of the steel tube, and convert it into the percentage of the length (in meters), which is the length of the steel tube. The full length of the bend.
For example, if the length of steel pipe is 8m and the maximum measured string height is 30mm, the full-length bending of the pipe should be:
0.03÷8m×100%=0.375%

Welded steel pipe
Welded steel pipe, also called welded pipe, is a steel pipe made by welding a steel plate or strip after crimping.
Welded steel pipe production process is simple, high production efficiency, variety specifications, equipment investment, but the general strength is lower than the seamless steel pipe. Since the 1930s, with the rapid development of high-quality strip continuous rolling production and the advancement of welding and inspection technologies, the quality of welds has been continuously improved, and the variety and specifications of welded steel pipes have been increasing, and they have been replaced in more and more fields. Steel pipe. Welded steel pipes are divided into straight seam welded pipes and spiral welded pipes in the form of welds.

Welded steel pipe - Steel pipe
Straight seam welded pipe
Straight seam welded pipe. Pipes made by hot-rolling or cold-rolled steel plates or steel strips and welded by straight seam welding on welding equipment are called longitudinally welded pipes. (Because the welding of the steel pipe became a straight line, it was named.)

20180517173801 25859 - Steel pipe
Large diameter straight seam welded pipe main production process description:
1. Prospecting: After the steel plate used for manufacturing large-diameter submerged arc welded straight seam steel pipes enters the production line, a full-plate ultrasonic inspection is first performed;
2. Milling: Double-sided milling of the two edges of the steel plate by the edge milling machine to achieve the required plate width, plate edge parallelism and groove shape;
3. Pre-crimping: Pre-bending machine is used to pre-bend the edge so that the edge of the board has a curvature that meets the requirements;
4. Forming: In the JCO molding machine, first half of the pre-bent steel plate is punched several times and pressed into a “J” shape. Then, the other half of the steel plate is also bent and pressed into a “C” shape to form an opening. The “O” shape
5. Pre-welding: seaming the formed straight welded steel pipe and using gas shielded welding (MAG) for continuous welding;
6. Internal welding: Use vertical multi-wire submerged arc welding (up to four wires) to weld inside the straight seam steel pipe;
7. Outer welding: use vertical multi-wire submerged arc welding to weld outside LSAW steel pipe;
8. Ultrasonic inspection I: 100% inspection of the internal and external welds of the longitudinal welded steel pipe and the base metal on both sides of the weld;
9. X-ray inspection I: 100% X-ray industrial television inspection of internal and external welds, using image processing systems to ensure detection sensitivity;
10. Expanding: Expand the length of the submerged arc straight seam steel pipe to increase the dimensional accuracy of the steel pipe and improve the distribution of the internal stress of the steel pipe.
11. Hydraulic pressure test: The root diameter of the expanded steel pipe is tested on the hydrostatic testing machine to ensure that the pipe meets the required test pressure. The machine has automatic recording and storage functions;
12. Chamfering: the pipe after passing the inspection is processed at the pipe end to meet the required pipe end groove size;
13. Ultrasonic inspection II: Ultrasonic inspections are performed one by one to check for possible defects in the longitudinal welded steel pipe after diameter expansion and water pressure.
14. X-ray examination II: X-ray industrial television inspection and tube-end weld seam inspection of steel pipes after diameter expansion and hydrostatic pressure testing;
15. Tube end magnetic particle inspection: This inspection is performed to find the tube end defects;
16. Anti-corrosion and coating: The qualified steel pipe is anti-corrosion and coating according to the user’s requirements.

Straight seam welded pipe inspection method
Q235B straight seam welded pipe quality inspection methods are many, of which physical methods are the most commonly used inspection methods, physical testing is the use of some physical phenomena to determine or test methods. Inspection of internal defects in materials or Q235B straight seam welded pipes is generally performed by non-destructive testing. The current non-destructive flaw detection includes magnetic flaw detection, ultrasonic flaw detection, ray detection, and penetrant flaw detection.
Magnetic inspection
Magnetic flaw detection can only detect the defects on the surface and near surface of the magnetic Q235B straight seam welded pipe, and only quantitative analysis can be performed on the defect. The nature and depth of the flaw can only be estimated based on experience. The magnetic force test uses magnetic fields to magnetize the magnetic flux generated by the ferromagnetic Q235B straight seam welded pipe to detect defects. According to the measurement of magnetic flux leakage method, it can be divided into magnetic powder method, magnetic induction method and magnetic recording method, of which the magnetic powder method is the most widely used.
Penetration inspection
Penetration testing is the use of certain liquid permeability and other physical properties to find and display defects, including two kinds of color testing and fluorescent inspection, can be used to check the surface of ferromagnetic and non-ferrous materials, defects.
Ray inspection
Radiographic inspection is a flaw detection method that uses ray-penetrating substances and attenuating properties in the material to detect defects. According to the different types of radiation used for flaw detection, it can be divided into three types: X-ray inspection, γ-ray inspection, and high-energy ray inspection. Due to the different methods of displaying defects, each type of radiographic inspection is divided into ionization, screen observation, photography, and industrial television. The ray inspection is mainly used to inspect the internal cracks, incomplete penetration, porosity, and slag inclusions of the Q235B straight seam welded pipe.
Ultrasonic inspection
Ultrasonic waves can be used for the inspection of internal defects due to reflections at the interfaces of different media in the propagation of metals and other homogeneous media. Ultrasonic waves can inspect any weldment material, defects in any part, and can find the defect location sensitively, but it is difficult to determine the nature, shape and size of the defect. Therefore, Q235B straight seam welded pipe ultrasonic flaw detection often used in conjunction with ray inspection.
Straight seam welded pipe standard control
1. The general welded pipe is used for the transportation of general lower pressure fluids such as water, gas, air, oil and heating steam.
2. Ordinary carbon steel wire bushings (GB3640-88) are steel pipes used to protect electric wires in electrical and industrial installations such as industrial and civil buildings and installation machinery and equipment.
3, straight seam welded pipe (YB242-63) is the longitudinal and parallel steel pipe. Usually divided into metric welded pipe, welded thin-walled pipe, transformer cooling oil pipe and so on.
4. Spiral seam submerged arc welded pipe for pressure fluid transport (SY5036-83) is a hot-rolled steel strip used as a tube blank, is often temperature spirally molded, and welded by double-sided submerged arc welding, used for spiral conveying of pressurized fluids. Steel pipe. The steel pipe has strong pressure bearing capacity and good welding performance. After various rigorous scientific tests and tests, it is safe and reliable to use. Large diameter steel pipe, high transmission efficiency, and can save investment in laying pipelines. Mainly used for the transportation of petroleum and natural gas pipelines.
5. Spiral seam high-frequency welded pipe (SY5038-83) for pressure-bearing fluid conveying is made of hot-rolled steel strip as tube blank, and is often temperature-screw-formed and welded by high-frequency lap welding method for pressure-bearing fluid conveying. Spiral seam high-frequency welding steel pipe. The steel pipe has strong pressure bearing capacity, good plasticity, and is easy to be welded and processed. After a variety of strict and scientific inspections and tests, it is safe and reliable to use, the diameter of the steel pipe is large, the transmission efficiency is high, and investment in laying pipelines can be saved. Mainly used for laying pipelines for transporting oil, natural gas, etc.
6. Spiral submerged arc welded steel pipe (SY5037-83) for low-pressure fluid delivery is a hot-rolled steel strip used as a tube blank, which is usually formed at a constant temperature, and is made of double-sided automatic submerged arc welding or single-sided welding. Submerged arc welded steel pipes for general low pressure fluids such as water, gas, air and steam.
Quenching and Tempering of Longitudinal Welded Pipes
The surface of the straight seam welded pipe is usually quenched and tempered and heat treated by induction heating or flame heating. The main technical parameters are surface hardness, local hardness and effective hardened layer depth. Vickers hardness tester can be used for hardness test. Rockwell or Rockwell hardness tester can also be used. The choice of test force (scale) is related to the effective hardened layer depth and the surface hardness of the straight seam welded pipe. There are three hardness scales involved here.
Vickers hardness tester is an important means to test the surface hardness of heat-treated straight seam welded pipe in Hunan. It can use a test force of 0.5 to 100 kg to test the surface hardened layer to a thickness of 0.05 mm. Its accuracy is the highest, and the heat treatment workpiece can be distinguished. The slight difference in surface hardness. In addition, the effective hardened layer depth is also measured by the Vickers hardness tester. Therefore, it is necessary to use a Vickers hardness tester for a unit that performs surface heat treatment processing or uses a large number of surface heat-treated Hunan straight seam welded pipes.
Surface Rockwell hardness tester is also very suitable for testing the hardness of surface quenched workpieces. The surface Rockwell hardness tester has three scales to choose from. It is possible to test various surface-hardened Hunan Longitudinal Welded Pipes with an effective hardening depth of more than 0.1mm. Although the accuracy of the surface Rockwell hardness tester is not as high as that of the Vickers hardness tester, it has been able to meet the requirements as a means of quality control and inspection of the heat treatment plant. In addition, it also has the characteristics of simple operation, easy use, low price, rapid measurement, direct reading of hardness value, etc., and the use of surface Rockwell hardness tester can quickly and non-destructively detect each batch of surface heat-treated Hunan straight seam welded pipe. . This point is of great significance for straight seam welded pipe processing and machinery manufacturing plants in Hunan.
Rockwell hardness tester can also be used when the surface heat treatment hardened layer is thick. When the heat-treated hardened layer thickness is 0.4-0.8mm, the HRA scale can be used. When the thickness of the hardened layer exceeds 0.8mm, the HRC scale can be used.
Vickers, Rockwell, and Superficial Rockwell values can be easily converted to each other and converted to standard, drawing, or user-defined hardness values. Corresponding conversion tables are given in the International Standard ISO, American Standard ASTM and Chinese Standard GB/T.
If the part requires a higher local hardness, can be used for induction hardening and other methods of local quenching heat treatment, such straight seam welded pipe in Hunan are usually marked on the drawing of the local quenching heat treatment location and local hardness values. The hardness test of straight seam welded pipe in Hunan should be conducted within the designated area. The hardness tester can use Rockwell hardness tester to test the HRC hardness value. If the hardened heat treatment layer is shallow, a Rockwell hardness tester can be used to test the HRN hardness value.
Other welded pipe
Welded steel pipe
It is cut into narrow steel strips from steel strips and then wrapped in tubes with a cold process. The special welder then welds one tube seam. External welds polished bright. The inner burr of the general welded pipe does not hit. Only precision welded pipes are used for internal burrs.
Corrosion protection: Welded steel pipe is a steel pipe with seams on the surface after the steel strip or steel plate is deformed into a round shape, a square shape or the like. According to different welding methods can be divided into arc welded pipe, high frequency or low frequency resistance welded pipe, gas welded pipe, furnace pipe, Bondi tube and so on. According to the shape of the weld can be divided into straight seam welded pipe and spiral welded pipe. Welded steel pipes are used in oil drilling, machinery, and manufacturing industries. Furnace welded pipes can be used as water gas pipes, etc. Large-diameter straight seam welded pipes are used for high-pressure oil and gas transmission, etc. Spiral welded pipes are used for oil and gas transmission, pipe piles, bridge piers and so on. Welded steel pipe has lower cost and higher production efficiency than seamless steel pipe.
Straight seam pipe
It is made of steel plates or strips that are bent and then welded. Divided into straight seam welded pipe and spiral welded pipe. According to the purpose, it can be divided into general welded pipe, galvanized welded pipe, oxygen welded pipe, wire bushing, metric welded pipe, idler pipe, deep well pump pipe, automotive pipe, transformer pipe, welded thin-walled pipe, welded special-shaped pipe and spiral welded pipe.
General welded pipe
Typically welded pipes are used to deliver low pressure fluids. Made of Q195A, Q215A, Q235A steel. It can also be made of other mild steels that are easy to weld. The steel pipe should be subjected to hydraulic pressure, bending, flattening and other tests. It has certain requirements on the surface quality, usually the delivery length is 4-10m, and often requires length (or multiple feet) delivery. The specification of the welded pipe is expressed by the nominal diameter (mm or inch). The nominal diameter is different from the actual one. The welded pipe has two kinds of common steel pipe and thickened steel pipe according to the specified wall thickness. The steel pipe is divided into two types according to the pipe end, with or without threads. Table 6-17 is the size of the welded steel pipe.
There is no need for electric welding machines and high-frequency-resistance straight seam welded pipes, and no cross-grounding lines are required. No painting is required, eliminating the need for complicated construction processes such as traditional fusion welding and bushings. Simply connect the straight pipe joint to the pipe, the threaded pipe joint to the theoretical weight of the round steel pipe and the junction box. After positioning, use a special tool to tighten (screw) the screw, and use the lock nut to lock the high frequency resistance joint of the terminal box. Can be set. The pipe bender can bend the corresponding arc with the bender.

Materials
Common domestic materials are generally Q235A, Q235B, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, 16Mn, 20#, Q345, L245, L290, X42, X46, X70, X80 and so on.
Among them, X42, X46, X56, X80 and other materials are API standard materials, which are not commonly used materials of China’s pipe materials.
Use
Straight seam steel pipe is mainly used in tap water projects, petrochemical industry, chemical industry, power industry, agricultural irrigation, and urban construction in China.
For liquid transport: water supply, drainage.
For gas transportation: gas, steam, liquefied petroleum gas.
Used for structural purposes: as a pile driving pipe, as a bridge; piers, roads, building structures, etc.
Spiral welded pipe
Spiral Welded Pipe: It is made by winding a low carbon carbon structural steel or low alloy structural steel strip into a blank according to a certain helix angle (called forming angle), and then welding it together. It can be used in a narrower way. Strip production of large diameter steel pipes. Its specifications are expressed in terms of outer diameter and wall thickness. The welded pipe should ensure that the hydrostatic test, the tensile strength and the cold bending performance of the weld be in compliance with the regulations.
Inspection process of spiral welded pipe
Raw Material Inspection – Leveling Inspection – Butt Welding Inspection – Forming Inspection – Internal Welding Inspection – Outside Welding Inspection – Pipe Cutting Inspection – Ultrasonic Inspection – Groove Inspection – Dimensional Inspection – X-ray Inspection – Hydrostatic Test – Final Inspection
In order to ensure product quality, we have established a comprehensive quality plan, on-site working procedures and inspection and test plans.
Advantages and disadvantages of spiral welded pipe
Spiral welded pipe advantages:
(1) The use of steel strips of the same width enables the production of steel pipes of different diameters, in particular the production of large-diameter steel pipes with narrow strip steel.
(2) Under the same pressure conditions, the spiral welds are subjected to a smaller stress than the straight seams, which is 75% to 90% of the straight seam welded pipes, and can therefore withstand greater pressures. Compared with the straight welded pipe with the same outer diameter, under the same pressure, the wall thickness can be reduced by 10% to 25%.
(3) Accurate size, general diameter tolerance is not more than 0.12%, deflection is less than 1/2000, ellipticity is less than 1%, and sizing and straightening processes are generally omitted.
(4) It can be continuously produced. In theory, it can produce infinitely long steel pipes, and the loss of cutting and cutting tails is small, which can increase the metal utilization rate by 6% to 8%.
(5) Compared with the straight seam welded pipe, its operation is flexible and the adjustment of the replacement type is convenient.
(6) The equipment is light and the initial investment is small. It can be made into a trailer-type flow unit and the welded pipe can be produced directly at the construction site where the pipeline is laid.
(7) It is easy to realize mechanization and automation.
The disadvantage of spiral welded pipe is: due to the use of rolled steel as raw material, there is a certain crescent of the crescent, and the welding point is in the edge zone of the elastic strip, so it is difficult to align the welding torch and affect the welding quality. To this end, complex weld seam tracking and quality inspection equipment must be set up.

Comparison of Spiral Welded Pipes and Longitudinal Welded Pipes
A simple comparison of the technical characteristics of spiral welded pipe and straight welded pipe:
Metallurgical properties of the material
LSAW pipes are produced from steel plates, and spiral welded pipes are produced from hot rolled coil plates. The rolling process of the hot strip mill unit has a series of advantages, and has the metallurgical process capability to obtain high quality pipeline steel. For example, a water cooling system is installed on the output stage to accelerate cooling, which allows the use of low-alloy compositions to achieve special strength levels and low temperature toughness, thereby improving the weldability of the steel. However, this system is basically absent from the steel plate production plant. Coil alloy content (carbon equivalent) is often lower than similar grades of steel, which also improves the weldability of spiral welded pipe.
It should be noted that since the spiral rolling direction of the spiral welded pipe is not perpendicular to the axial direction of the steel pipe (the solution depends on the helix angle of the steel pipe), the steel plate rolling direction of the straight seam steel pipe is perpendicular to the axial direction of the steel pipe. Thus, the spiral Welded pipe material has better crack resistance than straight seam steel pipe.
Welding process
From the welding process, the welding method of spiral welded pipe and straight seam steel pipe is the same, but the straight welded pipe inevitably has a lot of T-weld, so the probability of the existence of welding defects is also greatly improved, and the welding residue at the T-weld With higher stresses, the weld metal tends to be in a triaxial stress state, increasing the likelihood of cracking.
Moreover, according to the submerged-arc welding process specification, each weld should have an arc striking point and an arc extinguishing point. However, each straight-seam welding pipe cannot achieve this condition when welding a circumferential ring, and thus may have an arc extinguishing position. More welding defects.
Strength characteristics
When the tube is subjected to internal pressure, there are usually two main stresses on the tube wall, namely radial stress δY and axial stress δX. Weld seam synthetic stress δ = δY (l/4sin2α + cos2α) 1/2, where α is the spiral angle of the spiral welded pipe weld.
The helix angle of the spiral welded pipe weld is generally 50-75 degrees, so the synthetic stress at the spiral welded joint is 60-85% of the principal stress of the longitudinal welded pipe. At the same working pressure, the spiral welded pipe with the same pipe diameter can be reduced in wall thickness than the straight welded pipe.
Based on the above characteristics, we can see:
A. When the spiral welded pipe is blasted, because the normal stress and the resultant stress of the weld seam are relatively small, the blasting hole generally does not originate from the spiral weld seam, and its safety is higher than that of the longitudinal seam welded pipe.
B. When there are parallel defects near the spiral weld seam, the spiral weld seam is less stressed than the straight weld seam.
C. Since the radial stress is the maximum stress that exists on the steel pipe, the weld is subjected to the maximum load in the direction of the vertical stress. That is, the straight seam bears the largest load, and the circumferential welded seam has the smallest load and the spiral seam is between the two.
Static pressure blasting strength
Through comparative tests, it is verified that the yield pressure and burst pressure of the spiral welded pipe and the straight welded pipe are basically consistent with the measured value and the theoretical value, and the deviation is close. However, whether it is yield pressure or burst pressure, spiral welded pipe is lower than straight seam welded pipe. The blasting test also showed that the circumferential deformation rate of the spiral welded pipe blasting port was significantly greater than that of the straight seam welded pipe. From this, it was confirmed that the plastic deformation ability of the spiral welded pipe is better than that of the straight seam welded pipe, and the blasting port is generally limited to one pitch, which is caused by the strong constraint effect of the spiral welded joint on the expansion of the crack.
Toughness and fatigue strength
The trend of pipeline development is large diameter and high strength. With the increase of the diameter of the steel pipe and the improvement of the grade of steel used, the tendency is greater that the ductile fracture develops steadily. According to tests conducted by relevant research institutions in the United States, spiral welded pipe and straight welded pipe have a same level, but spiral welded pipe has higher impact toughness.
Because of the change in the transmission line, the steel pipe is subjected to random alternating loads during the actual operation. Understanding the low cycle fatigue strength of steel pipes is of great significance to determine the service life of pipelines.
According to the measurement results, the fatigue strength of the spiral welded pipe is the same as that of the seamless pipe and the electric resistance welded pipe. The test data is distributed in the same area as the seamless pipe and the resistance pipe, and higher than that of the ordinary submerged arc straight seam welded pipe.
Field weldability
The site’s weldability is mainly determined by the material of the steel pipe and the dimensional tolerance of the port.
Taking into account the requirements for the installation of steel tubes, the consistency of the continuity and shape geometry of the steel tube production is particularly important.
Spiral welded pipe production is a continuous process that is basically stable under the same working conditions: while the straight seam welded pipe manufacturing process is segmented, including the entire plate / indenter / pre-roll / spot welding / welding / finishing / group parity Multiple process procedures. This is an important feature of production of spiral welded pipe different from production of straight welded pipe.
The stable production conditions are very convenient for welding quality control and geometrical dimension assurance. Due to the regularity of the spiral welded pipe and the even distribution of the weld, the spiral steel pipe has a very good nozzle ellipticity and verticality of the end face with respect to the straight seam welded pipe, which ensures the accuracy of the spot welding accuracy of the spot welded steel pipe assembly.
Effect on the flow characteristics of the conveying medium
The pressure drop in the transfer line is proportional to the length of the pipe, the fluid viscosity coefficient, the fluid velocity, and the fluid resistance coefficient, and is inversely proportional to the internal diameter of the pipe. The fluid drag coefficient is related to both the Reynolds number and the roughness of the inner wall surface of the tube. It has been determined that the effect of roughness on the inner surface of the tube is ten times greater than that of the local bulge (such as a spiral weld or a longitudinal weld, or even an inner annular weld).
The straight seam welded pipe has a simple production process, high production efficiency, low cost, and rapid development. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe. A narrower blank can be used to produce a larger diameter pipe, and a blank having a different diameter can be produced from a blank of the same width. However, compared with the straight seam pipe of the same length, the length of the weld seam increases by 30 to 100%, and the production speed is low. Therefore, the smaller diameter welded pipe mostly adopts the straight seam welding, and the large diameter welded pipe adopts the spiral welding.
Low-pressure fluid transport welded steel pipe (GB/T3091-2008) is also called general welded pipe, commonly known as black pipe. It is a welded steel pipe used for the transportation of water, gas, air, oil and heating steam, and other generally lower pressure fluids and other uses. The wall thickness of the steel pipe is divided into ordinary steel pipe and thick steel pipe; the pipe end is divided into non-threaded steel pipe (light pipe) and threaded steel pipe. The welded steel pipe used for low-pressure fluid transportation is not only directly used for conveying fluids, but also used as a raw pipe for galvanized welded steel pipes for low-pressure fluid transportation.
1. Galvanized welded steel pipe for low pressure fluid delivery (GB/T3091-2008) Also known as galvanized welded steel pipe, commonly known as white pipe. It is a hot-dip galvanized welded (furnace or welded) steel pipe for general low pressure fluids such as water, gas, air oil, heating steam, and warm water. The wall thickness of the steel pipe is divided into ordinary galvanized steel pipe and thick galvanized steel pipe; the pipe end is divided into non-threaded galvanized steel pipe and threaded galvanized steel pipe. The specification of the steel pipe is expressed by the nominal diameter (mm), and the nominal diameter is the approximate value of the internal diameter. Commonly used in inches, such as 1/2, 3/4, 1,2 and so on.
2 Ordinary carbon steel wire bushings (YB/T5305-2006) are steel tubes used to protect electrical wires in electrical and industrial installations such as industrial and civil buildings and installation machinery and equipment.
3. Straight seam welded steel pipe (GB/T13793-2008) is a longitudinally parallel steel pipe of the weld seam. Used for general structure, usually divided into metric welded steel pipe, welded thin wall pipe and so on.
4. Spiral seam submerged arc welded steel pipe for pressure fluid transmission (SY/T5037-2000) is a hot rolled steel strip used as a tube blank, which is often temperature spirally molded, and welded by double-sided submerged arc welding method for pressurized fluid. Spiral seam steel pipe. The steel pipe has strong pressure bearing capacity and good welding performance. After various rigorous scientific tests and tests, it is safe and reliable to use. Large diameter steel pipe, high transmission efficiency, and can save investment in laying pipelines. Mainly used for the transportation of petroleum and natural gas pipelines.
5. Spiral seam high-frequency welded steel pipe (SY/T5038-2000) for pressure-bearing fluid transmission is a hot-rolled steel strip used as a tube blank, which is heated at regular temperature and spirally formed, and welded by high-frequency lap welding method. Fluid delivery spiral seam high-frequency welded steel pipe. The steel pipe has strong pressure bearing capacity, good plasticity, and is easy to be welded and processed. After a variety of strict and scientific inspections and tests, it is safe and reliable to use, the diameter of the steel pipe is large, the transmission efficiency is high, and investment in laying pipelines can be saved. Mainly used for laying pipelines for transporting oil, natural gas, etc.
7. General high-pressure spiral transmission high-frequency welded steel pipe (SY/T5039-2000) is a hot-rolled steel strip for tube blanks, regular temperature spiral molding, high-frequency lap welding method used for general low-pressure fluid transport High-frequency welded steel pipe with spiral joints.
8. Spiral welded steel pipe for piles (SY/T5768-2000) is made of hot-rolled steel strips as tube blanks, and is often spirally shaped. It is made of double-sided submerged arc welding or high-frequency welding. It is used for civil construction structures and piers. , bridges and other foundation pile steel pipe.

Calculation formula
Welded steel pipe weight kg/m = (Od – Wt) * Wt * 0.02466 Note: where Od is the outer diameter Wt is the wall thickness

Nominal caliber
Ordinary pipe
Thick pipe
(mm)
(in)
Outside diameter(mm)
Wall thickness(mm)
Theoretical weight(kg/m)
Wall thickness(mm)
Theoretical weight
(kg/m)
6
1/8″
10
2.00
0.39
2.5
0.46
8
1/4″
13.5
2.25
0.62
2.75
0.73
10
3/8″
17
2.25
0.82
2.75
0.97
15
1/2″
21.25
2.75
1.26
3.25
1.45
20
3/4″
26.75
2.75
1.63
3.5
2.01
25
1″
33.5
3.25
2.42
4
2.91
32
1 1/4
42.25
3.25
3.13
4
3.78
40
1 1/2
48
3.5
3.84
4.25
4.58
50
2″
60
3.5
4.88
4.5
6.16
65
2 1/2
75.5
3.75
6.64
4.5
7.88
80
3″
88.5
4
8.34
4.75
9.81
100
4″
114
4
10.85
5
13.44
125
5″
140
4
13.42
5.5
18.24
150
6″
165
4.5
17.81
5.5
21.63

Seamless steel pipe
Seamless steel pipe is a long strip steel with a hollow section and no joints around it. Seamless steel tubes have a hollow cross-section and can be used as pipes for transporting fluids, such as pipes for transporting oil, natural gas, gas, water, and certain solid materials. Compared with solid steel such as round steel, seamless steel tubes have a lighter weight when subjected to the same flexural and torsional strength, and are economical cross-section steels. They are widely used in the manufacture of structural and mechanical parts such as oil drill rods and automobile transmission shafts. , bicycle racks, and steel scaffolds used in construction. The use of seamless steel tubes to manufacture ring-shaped parts can increase material utilization, simplify manufacturing processes, save materials and processing man-hours, such as rolling bearing rings, jack sleeves, etc., are widely used in steel pipes. Steel pipe is also an indispensable material for various conventional weapons. The barrels, barrels, etc. must be made of steel pipes. Steel tubes can be divided into round tubes and shaped tubes according to the shape of the cross-sectional area. Since the circle area is the largest under the condition of the same circumference, more fluid can be transported by the circular tube. In addition, when the ring section is subjected to internal or external radial pressure, the force is more uniform. Therefore, most steel pipes are round pipes. However, the circular tube also has certain limitations. For example, under the conditions of plane bending, the circular tube is not as strong as the square and rectangular tube, and some agricultural machinery skeletons, steel-wood furniture, etc. are commonly used and rectangular tubes. According to different uses also need to have other cross-sectional shape of the special-shaped steel pipe.
Classification of seamless steel tubes
There are seamless steel tubes along the perimeter of its cross section. According to different production methods, it can be divided into hot-rolled tubes, cold-rolled tubes, cold-drawn tubes, extruded tubes, and top-tubes. Materials are common and high-quality carbon structural steel (Q215-A ~ Q275-A and 10 ~ 50 steel), low alloy steel (09MnV, 16Mn, etc.), alloy steel, stainless steel and other acid. Divided into general-purpose (for water, gas pipelines and structural parts, mechanical parts) and dedicated (for boilers, geological exploration, bearings, acid, etc.) by purpose.

The use of seamless steel pipe
Seamless steel pipe is widely used. General purpose seamless steel tubes are rolled from ordinary carbon structural steels, low alloy structural steels or alloy structural steels with the highest yield, and are mainly used as pipes or structural parts for conveying fluids. .

2, depending on the use of three different types of supply: a, according to chemical composition and mechanical properties of the supply; b, according to the mechanical performance of the supply; c, according to the water pressure test supply. Pipes supplied by Types a and b, if used to withstand liquid pressure, are also subject to hydrostatic testing.

3. The special-purpose seamless pipes include seamless pipes for boilers, chemical power, seamless steel pipes for geological use, and seamless pipes for petroleum.
Seamless steel tubes have a hollow cross-section and are used in large quantities as pipes for transporting fluids, such as pipes for transporting oil, natural gas, gas, water, and certain solid materials. Compared with solid steel such as round steel, steel pipes have a lighter weight when subjected to the same flexural and torsional strength and are economical cross-section steels.
Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile drive shaft, bicycle frame and steel scaffold used in construction, etc. The manufacture of ring-shaped parts using steel pipes can improve the material utilization, simplify the manufacturing process, save materials and processing Working hours have been extensively manufactured with steel pipes.

Seamless steel pipe production process
1 Hot Rolled Seamless Steel Tube Main Production Process (△ Main Inspection Process):
Tube blank preparation and inspection △→Pipe blank heating→Punching→Pipe rolling→Reheating of steel pipe→Determining (reducing) diameter→Heat treatment △→Production pipe straightening→Finishing→Inspection △ (Non-destructive, physical and chemical, table inspection) → Storage
2 Cold rolling (pulling) seamless steel pipe main production process:
Billet preparation → pickling lubrication → cold rolling (pulling) → heat treatment → straightening → finishing → inspection
General seamless steel pipe production process can be divided into two kinds of cold drawing and hot rolling. The production process of cold rolled seamless steel pipe is generally more complicated than hot rolling. The pipe blank must be firstly rolled by three rollers, and it must be pressed after extrusion. In the sizing test, if the surface does not respond to cracks, the circular tube must be cut by a mower to cut a blank having a length of about one meter. Then enter the annealing process, annealing with acidic liquids for pickling, pickling should pay attention to the surface whether there is a lot of blistering, if there is a large number of blisters generated that the quality of the steel can not meet the corresponding standard. Appearance of cold-rolled seamless steel pipe is shorter than hot-rolled seamless steel pipe, cold-rolled seamless steel pipe wall thickness is generally smaller than the hot-rolled seamless steel pipe, but the surface looks brighter than thick-walled seamless steel pipe, the surface is not too More rough, caliber does not have too many glitches.
The delivery status of hot-rolled seamless steel tubes is generally after hot-rolled and heat-treated. After the hot rolled seamless steel tubes undergo quality inspection, they must be strictly hand-selected by the staff. After the quality inspection, surface oiling is performed, followed by several times of cold drawing experiments, and after the hot rolling treatment, perforation tests are performed. If the perforation expansion is too large, straightening correction is required. After straightening, it is transported by the transmission device to the flaw detection machine to carry out the flaw detection experiment. Finally, it is labeled and placed in the warehouse after specification.
Round billet → heating → piercing → three-roller oblique rolling, continuous rolling or extrusion → de-spooling → sizing (or reducing) → cooling → straightening → hydrostatic test (or flaw detection) → marking → incoming seamless steel pipe The ingot is made by punching a steel ingot or a solid tube and then hot-rolled, cold-rolled or cold drawn. The specifications of the seamless steel pipe are expressed in millimeters of the outer diameter*thickness of the wall.
Hot-rolled seamless pipe outer diameter is generally greater than 32mm, wall thickness 2.5-200mm, cold-rolled seamless steel pipe outer diameter can be to 6mm, wall thickness can be to 0.25mm, thin-walled pipe outer diameter to 5mm wall thickness is less than 0.25mm, cold Rolling has higher dimensional accuracy than hot rolling.
Generally used seamless steel pipe is 10,20,30,35,45 and other high-quality carbon steel 16Mn, 5MnV such as low-alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB such as hot-rolled or cold rolled steel into. 10,20 and other seamless tubes made of low carbon steel are mainly used for fluid transportation pipelines. 45, 40Cr and other medium carbon steel seamless tubes are used to make mechanical parts, such as parts for cars and tractors. Generally used seamless steel pipe to ensure strength and flattening test. The hot-rolled steel pipe is delivered in a hot-rolled state or a heat-treated state; the cold-rolled steel is delivered in a heat-treated state.
Hot rolling, as the name suggests, has a high rolling temperature, so the deformation resistance is small, and a large amount of deformation can be achieved. Taking steel plate rolling as an example, the thickness of the continuous cast slab is generally about 230 mm, and after rough rolling and finish rolling, the final thickness is 1 to 20 mm. At the same time, due to the small aspect ratio of the steel plate, the dimensional accuracy requirements are relatively low, and the problem of plate shape is not easy to occur, and the convexity is mainly controlled. For the requirements of the organization, generally through the control of rolling and cooling to achieve, that is, control the finishing rolling temperature, finishing temperature. Round billet → heating → punching → start → annealing → pickling → oil (copper) → Multi-pass cold drawing (cold rolling) → blank tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → storage.
Mechanical properties of seamless steel tubes
The mechanical properties of steel are an important indicator to ensure the end-use performance (mechanical properties) of the steel. It depends on the chemical composition of the steel and the heat treatment system. In the steel pipe standard, tensile properties (tensile strength, yield strength or yield point, elongation), and hardness and toughness indexes, as well as high and low temperature performance required by users, are stipulated in accordance with different application requirements.
1 Tensile strength (σb)
The maximum force (Fb) at which the specimen is subjected to tensile breaking during the drawing process is divided by the stress (σ) obtained from the original cross-sectional area (So) of the specimen and is called the tensile strength (σb) in units of N/mm2 (MPa). It represents the maximum ability of a metal material to resist damage under the action of a tensile force.
2 Yield point (σs)
Metal material with a yield phenomenon, the specimen does not increase (hold constant) in the tensile process can still continue to stretch the stress, known as the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
The upper yield point (σsu): the maximum stress before the specimen first drops after yielding; the lower yield point (σsl): the minimum stress in the yield phase when the initial transient effect is not taken into account.
The formula for yield point is:
In the formula: Fs – the yield force (constant) during the tensile of the specimen, N (Newton) So – the original cross-sectional area of the specimen, mm2.
3 elongation after breaking (σ)
In the tensile test, the percentage of the gauge length and the original gauge length after the specimen is pulled off is called the elongation rate. Expressed in σ, the unit is %. The formula is: σ=(Lh-Lo)/L0*100%
In the formula: Lh–The gauge length after the specimen is broken, mm; L0–The original gauge length of the specimen, mm.
4 Section shrinkage (ψ)
In a tensile test, the percentage of the reduction in the cross-sectional area at the reduced diameter of the specimen after it is broken and the percentage of the original cross-sectional area is called the reduction of area. Expressed in ψ, the unit is %. Calculated as follows:
Where: S0 – the original cross-sectional area of the sample, mm2; S1 – the smallest cross-sectional area at the reduced diameter after the sample is broken, mm2.
5 hardness index
The ability of a metal material to resist the collapse of a hard object is called hardness. According to the test method and application range, the hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. For the pipe commonly used are Brinell, Rockwell, Vickers hardness three.
A, Brinell hardness (HB)
With a certain diameter of steel ball or cemented carbide ball, with the specified test force (F) pressed into the surface of the model, after the specified retention time to remove the test force, measure the indentation diameter (L) of the sample surface. The Brinell hardness value is the quotient obtained by dividing the test force by the ball surface area of the indentation. Expressed in HBS (steel ball), the unit is N/mm2 (MPa).
Its calculation formula is:
In the formula: F – the test force pressed into the surface of the metal specimen, N; D – the diameter of the test ball, mm; d – the average diameter of the indentation, mm.
The determination of Brinell hardness is more accurate and reliable, but generally HBS is only suitable for metal materials below 450N/mm2 (MPa), not for harder steel or thinner sheet. In the steel pipe standard, Brinell hardness is the most widely used, and the hardness of the material is often represented by the indentation diameter d, which is intuitive and convenient.
Example: 120HBS10/1000/30: indicates that the Brinell hardness value measured with a 10mm steel ball under a test force of 1000Kgf (9.807KN) for 30 seconds (seconds) is 120N/mm2 (MPa).
Seamless pipe quality requirements
(a) quality requirements
1 The chemical composition of steel: The chemical composition of steel is one of the most important factors affecting the performance of seamless steel tubes, and it is also the main basis for formulating the technical parameters of rolling tubes and the heat treatment parameters of steel tubes.
a. Alloying elements: intentionally added, depending on use
b. Residual elements: steel-making, proper control
c. Harmful elements: strict control (As, Sn, Sb, Bi, Pb), gas (N, H, O)
Out-of-furnace refining or electroslag remelting: Improve the uniformity of the chemical composition of the steel and the purity of the steel, reduce the non-metallic inclusions in the tube blank and improve its distribution.
2 Steel tube geometry accuracy and shape
a. Accuracy of outer diameter of steel pipe: It depends on the method of setting (reducing) diameter, equipment operation, process system, etc.
Permissible outer diameter deviation δ=(D-Di)/Di ×100% D: Maximum or minimum outer diameter mm
Di: nominal outside diameter mm
b. Accuracy of wall thickness of steel tube: related to heating quality of tube blank, process design parameters and adjustment parameters of each deformation process, tool quality and lubrication quality
Permissible wall thickness deviation: ρ=(S-Si)/Si×100% S: Maximum or minimum wall thickness on cross section
Si: nominal wall thickness mm
C. Steel tube ellipticity: indicates the degree of non-circularity of the steel tube.
d. Length of steel pipe: normal length, length (length), length allowable deviation
e. Bending of the steel tube: Denote the curvature of the steel tube: the bending of the length of the steel tube per meter, the bending of the entire length of the steel tube
f. Steel pipe end surface cut-off degree: It indicates the inclination of the steel pipe end surface and the cross-section of the steel pipe.
g. Steel pipe face angle and blunt edge
5. Steel tube surface quality: surface smooth requirements
a. Dangerous defects: cracks, infolding, outfolding, punctures, delamination, scabs, pulls, bulges, etc.
b. General defects: pits, green lines, scratches, bumps, minor internal and external straights, roll marks, etc.
Cause:
1 Due to surface defects or internal defects in the tube.
2 Produced during the production process, such as the design of rolling process parameters is not correct, the surface of the mold is not smooth, the lubrication conditions are not good, and the design and adjustment of the hole type are unreasonable.
3 During the heat rolling, heat treatment and straightening process of the tube blank (steel tube), if the heating temperature is not properly controlled, the deformation is not uniform, the heating and cooling rate is unreasonable, or the amount of straightening deformation is too large, resulting in excessive residual stress. It may also cause surface cracks in steel pipes.
6. Steel management performance: normal temperature mechanical properties, high temperature mechanical properties, low temperature properties, corrosion resistance. The physical and chemical properties of the steel pipe mainly depend on the chemical composition of the steel, the structure and purity of the steel, and the heat treatment method of the steel pipe.
7. Steel pipe process performance: flattening, flaring, crimping, bending, welding and so on.
8. Steel tube metallographic structure: low magnification (macro), high magnification (microscopic) M, B, P, F, A, S
9. Steel pipe special requirements: contract attachments, technical agreements.

(b) Quality inspection methods for seamless steel pipes:
1. Chemical composition analysis: chemical analysis, instrumental analysis (infrared C-S instrument, direct reading spectrometer, zcP, etc.).
1 Infrared C-S instrument: analysis of ferroalloy, steel raw materials, steel, C, S elements.
2 Direct reading spectrometer: C, Si, Mn, P, S, Cr, Mo, Ni, Cn, A1, W, V, Ti, B, Nb, As, Sn, Sb, Pb, Bi in the bulk sample
3N-0 instrument: gas content analysis N, O
2. Steel pipe geometry and shape inspection:
1 Check the wall thickness of the steel pipe: Micrometer, ultrasonic thickness gauge, no less than 8 points at both ends and record.
2 Steel pipe outer diameter, ellipticity check: Snap gauge, vernier caliper, ring gauge, measure the maximum point, the minimum point.
3 steel pipe length inspection: steel tape measure, manual, automatic length measurement.
4 Check the bending of the steel pipe: The ruler, the horizontal ruler (1m), the feeler ruler, and the thin line measure the bending per meter and the full-length curve.
5 steel pipe end face angle and blunt edge inspection: square, card board.
3. Steel surface quality inspection: 100%
1 artificial eye inspection: lighting conditions, standards, experience, logos, steel pipe rotation.
2 Non-destructive testing:
a. Ultrasonic flaw detection UT:
It is sensitive to the material surface and internal crack defects of various materials.
Standard: GB/T 5777-1996 Level: C5 level
b. Eddy current inspection ET: (electromagnetic induction)
Mainly sensitive to point (hole-shaped) defects. Standard: GB/T 7735-2004
Level: Class B
c. Magnetic Powder MT and Magnetic Flux Leak Detection:
Magnetic flaw detection, suitable for the detection of surface and near surface defects of ferromagnetic materials.
Standard: GB/T 12606-1999 Level: C4 level
d. Electromagnetic ultrasonic flaw detection:
No coupling medium is required, which can be applied to high-temperature, high-speed, rough dry steel pipe surface flaw detection.
e. Penetration testing:
Fluorescence, coloration, and detection of surface defects in steel pipes.
4. Steel management performance test:
1 Tensile test: measuring stress and deformation, determining material strength (YS, TS) and plasticity index (A, Z)
Longitudinal and transverse specimens Pipe section, arc type, round specimen (¢10, ¢12.5)
Small diameter, thin wall Large diameter, thick wall Calibration distance.
Remarks: Elongation of specimen after breaking is related to specimen size GB/T 1760
2 Impact test: CVN, notch type C, type V, work J value J/cm2
Standard sample 10×10×55(mm) Non-standard sample 5×10×55(mm)
3 Hardness test: Brinell hardness HB, Rockwell hardness HRC, Vickers hardness HV, etc.
4 Hydraulic test: test pressure, regulation time, p=2Sδ/D
5. Steel pipe process performance inspection process:
1 Flattening test: round sample C-shaped sample (S/D>0.15) H=(1+2)S/(∝+S/D)
L=40~100mm Unit length deformation coefficient=0.07~0.08
2 ring pull test: L=15mm No crack is acceptable
3 Flaring and crimping tests: 30°, 40°, 60° centering taper
4 Bending test: It can replace flattening test (for large diameter pipe)
6. Steel pipe metallographic analysis:
1 High magnification test (microscopic analysis): non-metallic inclusions 100x GB/T 10561 Grain size: grade, grade
Organization: M, B, S, T, P, F, A-S
Decarburization layer: inside and outside.
A method rating: A type – sulfide B type – oxide C type – silicate D – globular oxidation DS.
2 low magnification test (macro analysis): naked eye, magnifying glass 10x or less.
a. Acid etching test.
b. Sulfur test method (pipe test, showing low-grained tissue and defects, such as loose, segregation, subcutaneous bubbles, peeling, white spots, inclusions, etc.
c. Tower-shaped hairline test: The number, length and distribution of hair lines are examined.
(C) China’s current seamless steel pipe standards:
1. The current standard for seamless steel pipes: a total of 47 items including: GB 25 items HB 3 items 19 items for special use; basic 2 items products 45 items
2. Commonly used standards:
1 GB/T 2102-2006 Steel pipe acceptance, packaging, marking and quality certificate.
2 GB/T 17395-2008 Seamless steel pipe size, shape, weight and allowable deviation.
3 GB 5310-2008 Seamless steel pipes for high pressure boilers.
4 GB 9948-2013 Petroleum Cracking Seamless Steel pipes.
5 GB 6479-2013 Seamless steel pipes for high pressure chemical fertilizer equipment.
6GB 18248-2008 seamless steel pipes for gas cylinders.

Hot rolled seamless pipe
Hot-rolled seamless pipe/hot-rolled seamless steel pipe: Hot-rolling is relative to cold-rolling, cold-rolling is rolling performed below the recrystallization temperature, and hot-rolling is rolling performed above the recrystallization temperature.
Hot-rolled seamless steel pipes are divided into general steel pipes, low- and medium-pressure boiler steel pipes, high-pressure boiler pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes, and other steel pipes.
Advantages and disadvantages of hot rolled seamless pipes
Advantage
It can destroy the ingot casting structure, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic; to a certain extent, the bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.
Shortcomings
After hot-rolling, the non-metallic inclusions (mainly sulfides and oxides, and silicates) inside the steel are pressed into thin sheets and a delamination (sandwich) phenomenon occurs. Stratification greatly degrades the properties of the steel in the thickness direction, and it is possible that interlayer tearing occurs when the weld seam shrinks. The local strain induced by weld shrinkage often reaches several times the yield strain, which is much larger than the strain caused by the load.
Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase equilibrium under no external force. Hot rolled steel of various sections has such residual stress. The larger the section size of general steel, the greater the residual stress. Although the residual stress is self-balanced, it still has some influence on the performance of steel components under external forces. Such as deformation, stability, anti-fatigue and other aspects may have an adverse effect.
Hot-rolled steel products have poor control of thickness and width. We are familiar with thermal expansion and contraction, because at the beginning of hot rolling even if the length, thickness are up to standard, and finally there will be a certain negative difference after cooling, the wider the width of the negative difference, the thicker the more obvious the performance. So for large steels, there is no way to be too precise about the width, thickness, length, angle, and edges of the steel.
Cold rolled (dial) seamless steel pipe
Cold-drawn steel pipe is a kind of steel pipe, that is, it is classified according to different production processes, and is different from hot-rolled (expanded) pipe. In the process of expanding the capillary blank or raw material pipe, it is made by multi-pass cold-drawing processing, usually on a single-chain or double-chain cold-drawing machine of 0.5-100T. Cold-rolled (dial) steel pipe in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, oil cracking pipe, machining pipe, thick-walled pipe, small-caliber plus inner mold cold-drawn pipe other It also includes carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless thin-walled steel pipes, and special-shaped steel pipes. The cold-drawn steel pipe can have an outer diameter of 6mm, a wall thickness of 0.25mm, a thin-walled pipe outer diameter of up to 5mm, a wall thickness of less than 0.25mm, and an accuracy and surface quality that is significantly better than that of a hot-rolled (expanded) pipe. Constraints, their caliber and length are subject to certain restrictions.
In addition to general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, oil cracking pipes, and other steel pipes, it also includes carbon thin-wall steel pipes, alloy thin-wall steel pipes, stainless thin-wall steel pipes, and special-shaped steel pipes. . The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless steel pipe can reach 6mm, the wall thickness can reach 0.25mm, the outer diameter of thin-wall pipe can reach 5mm, and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling.
Cold-drawn steel pipes have undergone work hardening. During cold drawing, plastic deformation occurs in the metal. There are multiple slip systems inside the crystal. The dislocation movement intercepts each other. Many dislocations are pinned, causing the dislocation to accumulate, and the dislocation source stops. The above series of processes resulted in a decrease in the mobility of dislocations and a significant increase in dislocation density in the crystal. When the plastic deformation occurs further, the stress increases and the dislocations in the pinning begin to move, the screw dislocations slip, the edge dislocations cannot slip, and the dislocation intersection occurs, which increases the immobility order.
Therefore, by increasing the dislocation density within the metal by cold drawing, dislocation mobility is reduced, and it is difficult to generate dislocations and to displace dislocations, so that the hardness and strength of the metal material are improved. This is the metallurgical principle of cold drawing.
When cold-drawn, the steel pipe undergoes plastic deformation through a certain shape and size of the mold under the force. At present, the methods of drawing in production can be roughly divided into three types: reduced-diameter extubation, reduced outer extubation, and reduced inner extubation. When cold-drawing, the steel pipe under the action of pull-out force, positive pressure, and friction force occurs. Corresponding deformation, mostly through the diameter reduction, wall reduction and sizing three stages, and the corresponding deformation of the internal area of the corresponding stress, in which the axial tensile stress, radial and circumferential compressive stress, metal extubation process is always in The tensile and biaxial compressive stress states are the basic mechanical characteristics of the cold drawn pipe deformation process.

Measures to Prevent Horizontal Cracking of Seamless Steel Pipe in Cold Rolling
First, improve billet heating quality
(1) Heating is strictly according to the process requirements, and heating is performed using the upper limit temperature to eliminate low-temperature heating. If the carbon steel (1 ~ 45.) billet heating temperature than the original process to improve the 20 ~ 30 °C, the effect is good. After statistics, the gap in the following five months dropped by nearly 40%.
(2) For inclined bottom furnaces, it is necessary to dilute the material so that the billet is heated evenly and the appearance of the yin-yang surface is eliminated. At the same time, after closing the material, the furnace door is closed to reduce heat loss.
(3) Strictly control the rolling rhythm to ensure that the billet is heated thoroughly and no black heart phenomenon occurs. Avoid perforation black spiral phenomenon.
(4) Use high-quality heavy oil to ensure the heating quality of the billet.
Second, improve the accuracy of capillary thickness
(1) Correctly adjust the perforation and rolling tube process parameters, improve the precision of rolls and other tools and molds, and make the blanks and barren pipes deform evenly during perforation and tube rolling.
(2) Accurate adjustment of the centering position, installation of a roller device, so that the head can be aligned with the center of the blank to avoid punching eccentricity.
(3) Install and adjust the holding roller to hold the top bar tightly to prevent the top bar from sinking.
(4) Conduct equipment repairs to keep the equipment in good condition and ensure the capillary wall thickness accuracy.
(5) Strengthen management, often measure capillary wall thickness, and find problems in a timely manner.
Third, avoid capillary water cooling and rolling cold steel
Control and coordinate the production rhythm, so that the management of the deserted pipe on the stage before rolling is short. Ensure that the final rolling temperature of the steel tube is not lower than 850°C, ensure the internal structure of the steel tube is uniform, reduce the residual stress, moderate the pressure of the cooling water, prevent the water leakage phenomenon, avoid the local urgent water cooling of the steel tube, and cause partial cold-brittle phenomenon.
Fourth, to prevent the emergence of straight hairline and rolling phenomenon
To improve the quality of tooling and die, inspect the tooling frequently and find that the tooling is worn or unsatisfactory and replaced in time. Always check the surface quality of the capillary tube, find problems, and resolve them in time.
Fifth, improve the quality of hair wear
The surface defects such as the folds and outfoldings of the capillary tube must be cleaned and the width of the dressing should be more than 8 times the grinding depth. The grinding wheel must be planed after being polished. To improve the grinding quality.
Sixth. Annealing of the capillary after dressing
(1) Due to factors such as poor heating quality of the billets or low finish rolling temperature, the steel tubes have residual stress and other defects. After the tube annealing, the residual stress of the steel tubes is eliminated, the internal structure is improved, the plasticity is improved, and the cold drawing deformation is facilitated.
(2) After the steel pipe is ground, the work-hardening occurs in the repaired part, the stress concentrates, the hardness of the repaired grinding surface increases, the plasticity decreases, and the deformation resistance increases. After the capillary tube is reground and then annealed, work hardening and stress concentration due to grinding can be eliminated, and the grinding part can obtain the same good plasticity as other parts, which facilitates processing and deformation.
(3) Annealing after trimming of the capillary tube must meet the requirements of the annealing process, so that the capillary tube is heated evenly and thoroughly, so that the state of the defects can be fully recovered. Eliminate internal stress, reduce hardness, improve plasticity.

Production process of seamless steel pipe
Generally used seamless steel pipe: is used 10,20,30,35,45 and other high-quality carbon steel 16Mn, 5MnV such as low-alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB alloy steel such as hot or cold rolled into. 10,20 and other seamless tubes made of low carbon steel are mainly used for fluid transportation pipelines. 45, 40Cr and other medium carbon steel seamless tubes are used to make mechanical parts, such as parts for cars and tractors. Generally used seamless steel pipe to ensure strength and flattening test. The hot-rolled steel pipe is delivered in a hot-rolled state or a heat-treated state; the cold-rolled steel is delivered in a heat-treated state.
1. Hot rolling (extrusion seamless steel pipe): round billet → heating → piercing → three-roller oblique rolling, continuous rolling or extrusion → de-spooling → sizing (or reducing) → cooling → straightening → hydrostatic test (or Flaw Detection) → Mark → Inbound
2. Cold drawn (rolled) seamless steel tube: round tube blank → heating → piercing → start → annealing → pickling → oil coating (copper plating) → multi-pass cold drawing (cold rolling) → blank tube → heat treatment → straightening →Hydrostatic Test (Flaw Detection) → Marking → Storage
Calculation formula
(OD – wall thickness) * Wall thickness * 0.02466 = kg/meter (weight per meter)
Precision steel pipe
Precision steel pipe is a kind of high-precision steel pipe material after cold drawing or hot rolling. Due to the advantages of the inner and outer walls of the precision steel pipe with no oxide layer, high pressure, no leakage, high precision, high smoothness, no deformation due to cold bending, no flaring, no flat cracks, etc., they are mainly used to produce pneumatic or hydraulic components such as cylinders. The cylinder can be seamless or welded.
Precise steel tube with high dimensional accuracy, high internal and external surface finish, no heat oxidized film on internal and external surfaces after heat treatment of steel tubes, steel tube flaring, flattening without cracks, cold bending without deformation, and can withstand high pressure, for a variety of complex deformation and mechanical deep processing deal with.
Major producers of steel grades: 10, 20, 35, 45, 40cr, 42crmo, etc.
After consultation, other brands of precision seamless steel tubes can also be supplied.
The main production base: Wenzhou, Shandong, Jiangsu, Chengdu, Tianjin, Hebei and so on.
Chemical composition:

Grade
Chemical composition%
C
Si
Mn
S
P
Cr
10
0.07-0.13
0.17-0.37
0.35-0.65
≤0.035
≤0.035
20
0.17-0.23
0.17-0.37
0.35-0.65
≤0.035
≤0.035
35
0.32-0.39
0.17-0.37
0.35-0.65
≤0.035
≤0.035
45
0.42-0.50
0.17-0.37
0.50-0.80
≤0.035
≤0.035
40Cr
0.37-0.44
0.17-0.37
0.50-0.80
≤0.035
≤0.035
0.08-1.10
25Mn
0.22-0.29
0.17-0.37
0.70-1.00
≤0.035
≤0.035
≤0.25
37Mn5
0.30-0.39
0.15-0.30
1.20-1.50
≤0.015
≤0.020

The chemical composition of the precision tube of the alloy tube includes carbon C, silicon Si, manganese Mn, sulfur S, phosphorus P, and chromium Cr.
Alloy pipe is a seamless steel pipe, its performance is much higher than the general seamless steel pipe, because this kind of steel pipe contains more Cr, its high temperature, low temperature, corrosion resistance is not other seamless steel pipe than On the other hand, the use of alloy pipes in the petroleum, aerospace, chemical, power, boiler, military and other industries is more extensive.
Alloy management theory calculation:
(OD – wall thickness) * Wall thickness * 0.02483 = Weight per meter.
The material of the alloy tube is roughly: 16-50Mn, 27SiMn, 20-40Cr, 12-42CrMo
16Mn 12Cr1MoV T91 27SiMn 30CrMo 15CrMo 20G Cr9Mo 10CrMo910 15Mo3 15CrMoV 35CrMoV 45CrMo
Alloy tube classification:
Palladium alloy tubes are used for the separation of hydrogen and impurities.
The principle of palladium hydrogen purification is that hydrogen is adsorbed on the palladium tube wall when the hydrogen to be purified is passed to the side of the palladium tube at 300-500° C. Since the 4d electron layer of palladium lacks two electrons, it It can generate unstable chemical bonds with hydrogen (this reaction of palladium and hydrogen is reversible). Under the action of palladium, hydrogen is ionized into protons with a radius of 1.5×10 15 m, and palladium has a lattice constant of 3.88×10 − 10m (at 20 °C), it can be through the palladium tube, under the action of palladium and protons in conjunction with electrons and re-formation of hydrogen molecules, from the other side of the palladium tube to escape. On the surface of the palladium tube, gas that has not been dissociated is impermeable, so that high purity hydrogen can be obtained using a palladium tube. Although palladium has unique permeation properties for hydrogen, pure palladium has poor mechanical properties, is easily oxidized at high temperatures, has a low recrystallization temperature, and easily deforms and embrittles the palladium tube. Therefore, pure palladium cannot be used as a permeation membrane. By adding appropriate amounts of Group IB and Group VIII elements to palladium, a palladium alloy can be used to improve the mechanical properties of palladium. 11. Seamless steel tube for semi-axle casing (GB3088-82) is used to manufacture automotive axle bushings and drive axles. For high-quality carbon structural steels and alloy structural steels used in shell-shaft tubes, hot-rolled seamless steel tubes and palladium alloys contain approximately 30% to 30% of silver and less than 5% of other components (such as gold).
Of the currently used palladium alloys, about 20-30% of silver is contained, and the content of other components (such as gold, etc.) is <5%. The rate at which hydrogen permeates the palladium alloy is related to the temperature, the thickness of the membrane, and the pressure difference (P) between the raw hydrogen and the pure hydrogen on both sides of the penetrating contact. Increasing the temperature, increasing the P, and decreasing the thickness of the membrane will increase the hydrogen transfer rate. However, the increase in temperature will reduce the tensile strength of the permeable membrane. Therefore, the use temperature of the palladium tube is usually controlled at about 450°C. Some impurities can lead to palladium poisoning, deteriorate the permeability of the gas, and even destroy the membrane. Substances that can cause palladium poisoning include: mercury, arsenides, halides, oil vapors, sulfur and ammonia-containing substances, and dust. The palladium alloy can be made into a tube (called a palladium tube) or a diaphragm (called a palladium film).
ABS alloy pipe and special cold-melt adhesive are one of them widely used in building water supply and central air conditioning, especially in building water supply risers and central air-conditioning pipes. PC/ABS alloy can also be used to make automotive exterior parts such as car wheel covers. Mirror cover, taillight cover, etc. PC/ABS has good formability and can process large automotive parts such as automotive fenders.
As an important part of steel products, alloy pipes are divided into two categories, namely, seamless steel pipes (round billets) and welded steel pipes (boards and strips) because of their different manufacturing processes and the shape of the pipe blanks used.
The principle of palladium hydrogen purification is that hydrogen is adsorbed on the side of the palladium tube when the hydrogen to be purified flows into the side of the palladium tube at 300-500° C. Since the 4d electron layer of palladium lacks two electrons, it can not generate hydrogen. Stable chemical bonds (this reaction of palladium and hydrogen are reversible) under the action of palladium.
Galvanized pipe
Galvanized pipe, also known as galvanized steel pipe, hot dip galvanized and electrogalvanized two, hot galvanized galvanized layer thickness, with uniform coating, strong adhesion, long life and other advantages. Zinc electroplating has a low cost, the surface is not very smooth, and its own corrosion resistance is much poorer than hot dip galvanized pipe.
Galvanized steel pipes are divided into cold-plated tubes and hot-plated tubes. The former has been banned and the latter can be used temporarily.
Cold galvanized pipe
Cold galvanizing is electro-galvanizing, and the amount of galvanizing is very small, only 10-50g/m2, and its own corrosion resistance is much worse than hot galvanized pipe. Regular galvanized pipe manufacturers, in order to ensure quality, mostly do not use electroplating zinc (cold plating). Only those small businesses with small scale and outdated equipment use electro-galvanizing, and of course their prices are relatively cheap. Cold galvanized pipes are not allowed to be used as water and gas pipes in the future.
Hot dip galvanized steel
The steel pipe substrate and the molten plating solution undergo complex physical and chemical reactions to form a zinc-iron alloy layer having a corrosion-resistant structure. The alloy layer is integrated with the pure zinc layer and the steel pipe base body. Therefore, its corrosion resistance is strong.
After the development of hot-dip galvanized steel pipes from the 60s to 70s of the 20th century, the quality of products has been greatly improved. From 1981 to 1989, it was successively rated as the quality product of the Ministry of Metallurgical Industry and the National Silver Award. The output also increased for many years in succession, 1993. The output is over 400,000 tons. In 1999, the output was more than 600,000 tons, and exported to Southeast Asia, Africa, the United States, Japan, Germany and other countries and regions. Hot-dip galvanized pipes are often used as water pipes and gas pipes. The common specifications are +12.5 to +102 mm. Since the 1990s, due to the country’s emphasis on environmental protection, the control of highly polluting enterprises has become more and more stringent, and the “three wastes” produced in the production of hot-dip galvanized pipes have been difficult to solve, together with stainless steel welded pipes, PVC pipes and composite pipes, etc. The rapid development, as well as the promotion of the promotion of the use of chemical building materials by the State and the restriction of the use of galvanized steel pipes, have caused the development of hot-dip galvanized welded pipes to be greatly constrained and restricted, and hot galvanized welded pipes have subsequently developed slowly.[1]
The galvanized pipe, which is often said, is mainly used for conveying gas and heating. The galvanized pipe is used as a water pipe. After a few years of use, a large amount of rust is generated inside the pipe. The outflow of yellow water not only pollutes the sanitary ware, but also contains bacteria that grow on the unsmooth inner wall. Corrosion causes high levels of heavy metals in the water and seriously harms human health. In the 1960s and 1970s, the developed countries in the world began to develop new types of pipes and galvanized pipes were gradually prohibited. China’s Ministry of Construction and other four ministries also issued a document explicitly banned galvanized pipes from the year 2000.
Shaped seamless steel pipe
Shaped seamless steel tubes are the general term for seamless steel tubes of other cross-sectional shapes than circular tubes. According to the different shapes and sizes of steel pipe sections, they can be divided into equal-wall thickness special-shaped seamless steel pipes (code D), unequal wall thickness profiled seamless steel pipes (codenamed BD) and variable-diameter special-shaped seamless steel pipes (coded as BJ). Shaped seamless steel tubes are widely used in various structural parts, tools and mechanical parts. Compared with round tubes, shaped tubes generally have larger moments of inertia and section modulus, and have greater resistance to bending and torsion, which can greatly reduce the structural weight and save steel.
Seamless square tubes and seamless rectangular tubes also belong to special-shaped seamless steel tubes. The calculation method of the seamless moment management theory weight: (side length + side length) × 2 × wall thickness × 0.00785 × length; seamless management theory weight Calculation method : Side length x4x Wall thickness x 0.00785 x Length

Source: Network Arrangement – China Steel Pipes Manufacturer – Yaang Pipe Industry (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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  • FLANGE

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References:

  • [1]. Editor-in-Chief of Xue Zhengliang. Introduction to Iron and Steel Metallurgy. Beijing: Metallurgical Industry Press, 2016.04.
  • [2]. Wang Tingzhao. Modern Steel Rolling Technology. Beijing: Metallurgical Industry Press, 2014.08.
  • [3]. Editorial Committee of Metallurgical Construction, editorial board of China Metallurgical Encyclopedia, editorial department of China Metallurgical Encyclopedia, Metallurgical Industry Press. China Metallurgical Encyclopedia, Metallurgical Construction, Beijing: Metallurgical Industry Press, 1999
  • [4].www.yaang.com

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