Expansion Joints: Everything You Need To Know

Expansion joints are flexible components that can effectively play a role in compensating for axial deformation. For example, welded in the fixed tube plate heat exchanger shell on the expansion joint axial flexibility, easy deformation, can compensate for the difference in thermal expansion of the tube and shell due to different wall temperatures, reducing their axial load, thereby reducing the tube, tube plate and shell temperature stress, to avoid causing strength damage, instability damage and tube pull-off damage. There are more types of expansion joints, commonly used waveform, ring plate welding and shell structure, among which waveform expansion joints are most widely used, ring plate welding expansion joints are only suitable for atmospheric pressure or low pressure occasions.

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What is an expansion joint?

The expansion joint, also known as compensator, is a flexible structure set on the vessel shell or pipeline to compensate the additional stress caused by temperature difference and mechanical vibration. Expansion joints are divided into metal expansion joints and non-metallic expansion joints.

What is a metal expansion joint?

A metal expansion joint is a device that allows for movement within a piping system. It can be used in both industrial and residential applications to prevent stress on the system, extend the life of the system, and help with thermal expansion or contraction.

Metal expansion joints are different from compression joints because they allow for lateral movement of pipes relative to one another while preventing axial movement of one pipe relative to another (though there are some exceptions).

Metal expansion joints are devices containing one or more bellows elements that can be used to compensate for the displacement caused by pressure and media flow in a piping system when pressure and media flow are present.
In addition, frequent thermal expansion, equipment displacement, vibration or pressure pulsation can cause the displacement of the piping system. If the piping system itself is not designed to be more flexible to cope with these displacements, metal expansion joints are an ideal choice.

Characteristics of expansion joint

Compensation function
Under the same overall dimensions, the compensation function of non-metallic expansion joints is much greater than that of metal expansion joints. Especially for the compensation function of lateral displacement, the compensation function of non-metallic expansion joints is almost one order of magnitude larger than that of metal expansion joints.
Compensation for resistance
The expansion joint is like an elastomer, which will produce resistance after being shrunk or stretched. The resistance of metal expansion joints is much greater than that of non-metallic ones. This resistance is too big, which is bad for the system and will damage the surrounding equipment.
High temperature and corrosion resistance
The materials of non-metallic expansion joints not only have good high temperature resistance, but also have acid and alkali resistance. The yield limit of ordinary carbon structural steel is equal to zero at 600 ℃, and the higher the temperature is, the scaling will occur. Carbon steel expansion joints are easy to crack during operation, and stainless steel expansion joints will suffer from low leakage point corrosion under low temperature environment, and the cost is considerable.
Thermal insulation and energy saving performance
The structure of non-metallic expansion joint itself has thermal insulation performance. However, the metal expansion joint does not meet this requirement. In order to preserve heat, the outer layer of the metal expansion joint is also covered with an insulating layer.
05 Maintenance and replacement performance
The non-metallic expansion joint needs no maintenance during its normal service life; It is much more convenient to replace non-metallic expansion joints than metal expansion joints.
Service life
The service life of the expansion joint is closely related to the environmental conditions. The non-metallic expansion joints have good wear and corrosion resistance. Relatively speaking, the service life of non-metallic expansion joints is longer than that of metal expansion joints under the same conditions.
Working pressure
Thanks to the flexible design and special materials used, non-metallic expansion joints can withstand greater working pressure.
Using Media
Metal expansion joint is applicable to liquid, gas and powder. The non-metallic expansion joint can be either a gas or a liquid.
Rubber expansion joint
An important category of non-metallic expansion joints, it has a large displacement compensation capacity, can compensate axial, transverse and angular displacement, and has the ability to reduce noise, vibration and corrosion.

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The working principle of the compensator

Tilt placed compensator upper end observation cover removed with probe oil dipstick inserted vertically to the bottom of the box, when an unconstrained compensator applied to the pipeline system after the force in the pipeline will be absorbed by the compensator without causing impact on the pipeline system itself. The compensation volume can reach 1800mm, and it is generally appropriate to use a group of rotating compensators according to 200m-500m. The small tie rod on the compensator is mainly a rigid support during transportation or as a product pre-deformation adjustment, it is not a force-bearing.
As the reaction of external conditions is also the main element of the compensator fault, so we need to enhance its performance such as anti-erosion. The oil level of rotary compensator is 285mm-300mm, the oil level of sleeve compensator is 215mm-225mm, the oil level of sphere compensator is 195mm-205mm. the compensator transmission is smooth, vibration, shock and noise are small, the reduction ratio is large, and can be used with various mechanical equipment.
Compensator pressure and thrust is the force generated by the pressure applied to the compensator. This force is derived by multiplying the system pressure by the effective area of the compensator. Without the compensator, the piping system is affected by the pressure and the compensator does not move because the piping is in the opposite direction to the tension. Under different operating conditions, such as temperature, vibration conditions, displacement, pressure and other factors at the time of operation, the life of the compensator will change.
Capable of clearing errors due to pipe installation. The compensator can obtain a large transmission ratio with a single-stage drive, compact structure, the compensator has a good self-locking, and can save braking device for mechanical equipment with braking requirements. Compensator and seal surface friction loss is larger, so the transmission efficiency is lower than the gear, easy to heat and higher temperature. Compensator remove the fixing bolt, screw the nut to the bolt and keep it properly. Check the upper shell crippled and cracked.
Compensator seal assembly mark and remove the bearing end cover. If there are any abnormalities such as missing bolts, confirm that they are correct and then lift the upper shell with the top wire and lift it up on the prepared base plate. Measure the clearance of each compensator with plug ruler or lead wire pressure method, and measure more points for each compensator and make records. Drain the lubricant from the compensator and store it in the pipe.

What are the types of expansion joint?

Metal expansion joints

① Bend type expansion joint
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Figure.1 Bend type expansion joint
Bend the tube into a U-shaped or other shape (Figure 1), also known as up force bend. It is an expansion joint that uses the elastic deformation capacity of the shape to compensate. Its advantages are good strength, long life, can be made in the field, the disadvantage is to occupy a large space, consume more steel and friction resistance. This kind of expansion joint is widely used in various steam pipes and long pipes.
Bellows expansion joint
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Figure.2 Bellows expansion joint
Bellows expansion joint is a kind of expansion joint made of metal bellows. It can expand and contract along the axis of the pipe, and also allows a small amount of bending. Figure 2 shows a common axial type bellows expansion joint, which is used for axial length compensation on the pipeline. In order to prevent exceeding the allowable compensation amount, protective ties or rings are set at both ends of the bellows, and guide brackets are set at both ends of the pipe connected to it. There are also corner and lateral expansion joints, which can be used to compensate for corner deformation and lateral deformation of the pipe. The advantages of these expansion joints are space saving, material saving, easy standardization and mass production, but the disadvantage is the short life span. Bellows expansion joints are generally used for pipelines with not very high temperature and pressure and short length. With the improvement of the technical level of bellows production, the application range of these expansion joints is expanding. At present, bellows expansion joints can be used in the highest pressure of 6.0 MPa pipe system.
③ Sleeve expansion joint
Casing expansion joint consists of inner and outer casing which can make axial relative movement. The inner and outer sleeves are sealed by a stuffing box. When used, the tube at both ends is kept moving in one axis. The product mainly consists of sleeve (core tube), shell, sealing material, etc. Used to compensate the axial expansion of the pipe and the axial rotation of any angle. With a small volume of compensation is suitable for hot water, steam, grease media, through the sliding sleeve to the outer sleeve of the sliding movement, to achieve the compensation of thermal expansion.
The inner sleeve of the sleeve compensator is connected to the pipe, using the principle and structure of high performance self-pressure dynamic seal, which can slide freely in the shell with the expansion and contraction of the pipe, and can adapt to the sealing requirements of any pipe. New synthetic material is used to seal between the shell and the inner sleeve, which can resist high temperature, corrosion and aging, applicable temperature from -40 to 150, and up to 350 in special cases.

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Figure.4 Sleeve expansion joint

Non-metallic expansion joints

① Rubber duct expansion joint
Duct rubber compensator is divided into FDZ, FVB, FUB, XB four types, by rubber and rubber a fiber fabric composite material, steel flange, sleeve, insulation materials, mainly used for a variety of fans, flexible connection between the duct, its function is shock absorption, noise reduction, sealing, media resistance, easy displacement and installation, is an ideal in the field of environmental protection, shock absorption, noise reduction, smoke and dust removal It is a kind of ideal supporting parts for vibration damping, noise reduction, smoke and dust removal in the field of environmental protection.
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Figure.4 Expansion joint of power plant boiler
② Fiber fabric expansion joint
Fabric compensator is mainly fiber fabric, rubber, and other high temperature resistant materials. Can compensate for vibration and pipe deformation of fan and duct operation. Fiber fabric expansion joint can compensate axial, transverse, angular products, with no thrust, simplified support design, corrosion resistance, high temperature resistance, muffling vibration reduction, etc., especially suitable for power plant hot air ducts and soot ducts. Non-metallic compensator in the fiber fabric, insulation cotton body itself has the function of sound absorption, vibration isolation, can effectively reduce the noise and vibration of boilers, fans and other systems. Simple structure, light body, easy maintenance.

What is an expansion joint used for?

Expansion joints are used to reduce stress on a system that is undergoing thermal growth, such as piping and mechanical structures. Metal expansion joints are designed with a coil spring that absorbs the movement of your system.

Why do we use expansion joints?

It is widely used in modern industry. On heating, in order to prevent pipeline deformation or damage caused by thermal elongation or temperature stress when heating pipeline heats up, it is necessary to set compensators on the pipeline to compensate for the thermal elongation of the pipeline, so as to reduce the stress on the pipe wall and the force acting on the valve or support structure.

  • Compensation to absorb pipeline axial, lateral, angular cold and heat deformation.
  • Corrugated compensator expansion, to facilitate the installation and removal of the valve pipeline.
  • Absorption of equipment vibration, reduce the impact of equipment vibration on the pipeline.
  • Absorb the amount of deformation of the pipeline by earthquake and ground subsidence.

The role of metal compensator in different industrial fields

Metal compensators are widely used in the industrial field. For example, high-temperature corrugated compensators will be used in the high-temperature gas transmission pipeline of the metallurgical industry, corrosion resistant corrugated compensators will be used in the chemical industry, and different types of corrugated compensators will be involved in the cement industry, the power industry, and the construction industry; Different natural environments also affect the selection of corrugated compensator. Generally, there is no supporting heat pipe network in the warmer southern cities, while there will be a large number of corrugated compensator applications in the heat pipe network in the colder northern cities. Therefore, to determine the type of the applied ripple compensator in a certain area, it is necessary to know the environment and industrial constitution of that area.
The high-temperature resistant metal bellows compensator is composed of bellows, guide barrel, end pipe and connectors. The bellows is the core component of the compensator. High temperature resistant bellows compensator shall be manufactured according to two temperature standards, one is below 1000 ℃ and the other is above 1000 ℃. Under 1000 ℃, it can be made in the form of pure stainless steel corrugated compensator. Generally, 321 stainless steel (used within 550 ℃) and 310S stainless steel (used between 600 ℃ and 1000 ℃) can be selected. According to the technical requirements provided by the customer, the high-temperature bellows compensator of this batch should be made of 310S stainless steel in the form of pure stainless steel to achieve the temperature resistance of 900 ℃.
Application of metal compensator in hot blast furnace pipeline — hot blast furnace hot blast pipeline is a high temperature and high pressure pipeline. Under the influence of high temperature, the pipeline will be subject to thermal expansion, causing the hot blast pipeline to shift. In serious cases, the hot blast pipeline will leak, affecting the system operation and production. These problems have been solved one by one with the successful application of bellows compensator in high-temperature pipeline.
The corrugated compensator used in the hot blast furnace pipeline is called ‘high-temperature corrugated compensator’ or ‘high-temperature resistant corrugated compensator’. The corrugated compensator is made of stainless steel composite thermal insulation material with good high temperature resistance. It can compensate the axial translation of the hot air pipe and solve the outstanding problems such as pipe dislocation and air leakage caused by pipe translation. At present, the temperature resistance level of the bellows compensator can reach 1300 ℃. That is to say, it meets the technical specifications and performance of the hot blast stove. The metal corrugated compensator is generally used in the pipeline system with higher pressure or temperature, while the non-metallic compensator is generally used in the air duct. In contrast, the application scope of metal corrugated compensator is relatively wide.

Design Limits of Metal Expansion Joints

Metal expansion joints are flexible connectors that help to prevent stress from thermal growth on your system.

Design limits are the maximum and minimum temperatures that the expansion joint is designed to withstand. Design limits are based on the material and size of the expansion joint, as well as whether it will be used in continual or intermittent service.

If you’re using your expansion joint for continuous service, then its design limits are based on its temperature rating (for example: 300°F, 350°F or 400°F). This means that if you select a 400°F rated metal expansion joint and install it in an area where temperatures may exceed 400°F (like right next to a boiler), then this could cause damage to your metal expansion joint over time. You should consider selecting a lower temperature rated metal expansion joint so that it does not get damaged when exposed to higher temperatures during operation.

Movements – What kind of movements can an expansion joint absorb?

There are three basic types of movement that can be applied to the expansion joins and these are: Axial movement, Lateral movement and Angular deflection as illustrated below.

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     Axial movement

Axial movement is the free length of the expansion joints stretching or compressing along its longitudinal axis.

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   Lateral movement

Lateral movement is a movement of the two ends of the expansion joints where those ends stay parallel to each other but not in one plane.

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 Angular deflection

Angular deflection is the displacement of the longitudinal axis of the Expansion joint from its initial straight line position in to a circular arc.

Cycle life

This is the primarily the most important factor in good bellows design. In addition to the stroke, the cycle life required determines the number of convolutions needed in the bellow elements and this also determines the amount of stress acting upon the bellow elements.

Pressure thrust

Pressure thrust is the force created by pressure acting on a bellows. This force is the system pressure times the effective area of the bellows. When a piping system without expansion joints is pressurized, the system will not move because the pipe is countering the force in tension. When an unrestrained expansion joint is introduced in the network, the force tends to pull the ends away from the expansion joint causing damage to itself and the pipe. This pressure thrust must be contained with either main anchors or restrained expansion joints designed to carry pressure thrust loads. The main anchors must be able to resist the pressure thrust force and a small amount of force due to the deflection of the bellows.

Accessories- How can I upgrade my expansion joint to handle different conditions?

Limit rods: a “fail-safe” addition which addresses the situation of occasional anchor overload or system malfunction which could cause expansion joints beyond tolerance.

Liners: internal liners used to protect the internal surface of the metal bellows from media which may compromise its integrity.

Connections: used in tandem with liners, keep the bellows within high temperature tolerance conditions, such as oil industry applications.

Covers: are used to protect the expansion joints from any detrimental external elements.

Pipe Alignment Guides: control thermal expansion in the system so that the movement applied to the bellows assembly is axial only.

Sizing of Metal Expansion Joints

  • Sizing is determined by the length of the expansion joint.

  • The length of an expansion joint is determined by the length of pipe run.

  • The distance between these two points determines where you want to connect your pipes.

Testing of Metal Expansion Joints

Testing is required to ensure the design limits are met. Testing can be done in a lab or on site, using pressure tests or thermal tests.

The pressure test uses compressed air to simulate water flows through the expansion joint and measures any leakage at pre-determined pressures. A thermal test measures pipe temperatures as well as changes in the alignment of pipes caused by differing amounts of expansion and contraction over time. This allows for more accurate calculations of how much movement you can expect from your system over time, all while ensuring that it’s not too much movement—which could lead to stress fractures or other structural issues with your piping system.

Material selection principle of expansion joint

  • 1. Corrugated expansion joints made of carbon steel and low alloy are only applicable to t ≤ 375 ℃; The corrugated expansion joint made of austenitic stainless steel is applicable to t ≤ 500 ℃.
  • 2. Corrugated expansion joints made of carbon steel or low alloy steel shall have a corrosion allowance of no more than 1mm, otherwise austenitic stainless steel shall be used.
  • 3. For medium prone to corrosion such as chloride, sulfide, acid and alkali or high working temperature (more than 550 ℃), corrosion resistant alloy or superalloy shall be selected to manufacture expansion joints, such as domestic materials FN-2, NS111 and B-315 or Incoloy800 and 825.

General materials for expansion joints

  1. Super austenitic special stainless steel: 254SMO, 904L, AL6XN.
  2. Duplex stainless steel: 2205 duplex steel (S31803).
  3. Nickel-based alloy steel: INCOLOY800/800H/800HT/840/825, INCONEL600/601/690/625/X-750.
  4. Hastelloy C-276/C-22/X, MONEL400/K500.
  5. Pure nickel: N4, N6 (Ni200, Ni201).
  6. Titanium: GR1, GR2, TA1, TA2.
  7. Austenitic stainless steel: SUS304, SUS304L, SUS316, SUS316L, SUS310S, SUS321, SUS316Ti.

Manufacturing process of expansion joint

Expansion joints are also customarily called expansion joints. It consists of a bellows (an elastic element) that forms the main body of its work and accessories such as end pipes, brackets, flanges and conduits. Expansion joint is a compensating element. It uses the effective expansion and contraction deformation of the bellows, which is the main body of work, to absorb the dimensional changes of pipelines, ducts, containers, etc. caused by thermal expansion and contraction. Because the expansion joint has compensation to absorb pipeline axial, lateral, angular thermal deformation, corrugated compensator expansion, facilitate the installation and removal of valves and pipes, absorb equipment vibration, reduce the impact of equipment vibration on the pipeline, absorb earthquakes, subsidence on the deformation of the pipeline and other roles, and therefore in modern industrial production has been widely used.

1. Technical points of manufacturing expansion joints

The technical points of manufacturing expansion joints are pipe billet manufacturing, bellows manufacturing and expansion joint assembly welding. Seamless pipe billet and welded pipe billet, seamless pipe billet is generally used in the manufacture of pressure processing methods such as spinning stretching and rolling, for smaller diameter pipe billet manufacturing; while the diameter of the corrugated expansion joint is larger, so most of the use of welded pipe billet. Corrugated pipe billet welding can be used tungsten DC hydrogen arc welding, tungsten pulse hydrogen arc welding, micro-beam plasma welding, melting pole argon arc welding and other methods. The factory inspection of the expansion joint mainly includes the above-mentioned appearance inspection, geometric dimension inspection and pressure inspection. For expansion joints with special requirements, according to the use of working conditions, process requirements, etc., according to the agreement between the supply and demand for other methods of inspection, such as gas tightness test, leakage and coloring, nondestructive testing, etc.

2. Pipe billet manufacturing process

The basic process of manufacturing expansion joint billets is plate shearing – rolling – cleaning before welding – billet welding – billet rounding – billet set. Plate shear, according to the process layout and process card requirements, adjust the positioning of the shear stopper (or scribe on the plate), and then cut the plate. After the first cut, the size should be checked, after passing the batch shear, and every interval a certain number of random checks. Inspection items are circumferential length and height, straightness of the cut, the verticality of the two adjacent sides. Roll, the shear plate according to the size of the diameter of the rolled plate machine rolled into a cylinder. For the diameter and wall thickness ratio is larger, can be freely bent into a round simple billet can not be rolled. Cleaning before welding, in order to ensure the quality of welding, must be cleaned before welding, welding joints must not have oil and dust, anhydrous ethanol can be used to clean the surface to be welded, dry as soon as possible after welding, welders in the welding assembly operations do not directly touch the surface to be welded with their hands. Pipe billet welding, according to the welding specification parameters on the process card to adjust the billet welding machine, the billet in the welding fixture clamped, and then welded. After welding piece by piece inspection, there should be no burn through and not welded through and other weld defects, weld depression (or residual height) and the amount of misalignment should be less than 10% of the plate thickness. Pipe billet rounding, in the coil machine on the pipe billet rounding. The billet set, multi-layer bellows in the manufacturing process, the gap between the layers should be less than or equal to the thickness of a single layer of the plate.

3. Corrugated pipe manufacturing requirements

  • 1) The bellows should be formed by hydraulic, rolling or stamping and other integral forming methods.
  • 2) Corrugated pipe forming with thin rolled pipe billet is only allowed to have a full weld through the butt longitudinal seam, not allowed to have a circumferential weld.
  • 3) The longitudinal weld seam of the billet should be color penetration flaw detection or ray flaw detection before forming the corrugated pipe, and pay attention to the inspection of the surface quality.
  • 4) The weld seam of the pressurized cylinder section should be subject to local radiographic flaw detection, and the proportion is generally 20%.
  • 5) The connection between the bellows and the pressurized cylinder section ring weld is appropriate for the full weld through the wall thickness of the bellows butt type weld, the connection form is inserted shape or jacket shape.

4. Corrugated pipe manufacturing process

At present, the main methods of forming bellows are hydraulic forming, mechanical expansion and roll forming. Hydraulic forming and roll forming is the more traditional bellows forming method, in the small diameter of the bellows forming most of the hydraulic forming method; the large diameter of the bellows is generally used to roll forming, but roll forming can usually only roll single-layer bellows. Mechanical expansion is a more advanced forming method developed in recent years, compared with hydraulic forming, production efficiency increased by more than 10 times, labor intensity is also greatly reduced. In forming large diameter multi-layer corrugated pipe, the port does not need to be sealed, but also to ensure the cleanliness of the corrugated pipe layers. And the equipment is simple, small investment, more than 100mm diameter of the corrugated pipe can be used mechanical expansion method. When the bellows mechanical expansion using a circular inner mold, which consists of a number of mold flaps. Corrugated pipe manufacturing process is as follows: corrugated forming – corrugated pipe end seam welding – corrugated pipe port shear. Corrugated forming, the set of billet set in the mechanical expansion of the outside of the film, to determine the location of the first wave, and then start the hydraulic press, the die flap in the hydraulic press under the action of the outward movement of the mold, so that the billet formed out of the corrugation, when the shape of the corrugation in line with the requirements of the drawing or process card, due to the role of the limit device in the mold, the outward movement of the die flap is restricted no longer in motion. At this time, the hydraulic press will be opened to the return direction, the cone in the mold and the mold flap under the action of the reset spring, with the return movement of the hydraulic press gradually reset. After the complete reset, the billet will be moved a certain distance, and then repeat the above steps to form the second corrugation. So on and so forth, until the required number of corrugations are formed. The corrugated pipe end seam welding, because the multi-layer corrugated pipe is composed of multi-layer thin-walled cylinder, in order to ensure the quality of welding between the corrugated pipe and the connector, resistance seam welding should be used to fuse the end edge into a single layer, so that the corrugated pipe and the connector welding process becomes good, reliable welding quality, not easy to appear between the layers of leakage. According to the length of the straight edge section positioned by the process card, according to the wall thickness and the number of layers selected welding specifications for welding. In general, water cooling is commonly used in resistance seam welding, but water cooling is prohibited in bellows end seam welding, because if cooling water enters between the layers of bellows, after both ends are welded, the bellows layer is a sealed space. In the use of bellows, if the use of high temperature, residual water in the bellows layer between the rapid vaporization, so that between the bellows layer due to the vaporization of water generated very large pressure, causing damage to the bellows. Corrugated pipe port shear, according to the drawings or process card requirements for the length of the straight edge section of the port shear, shear methods are as follows: the use of manual or electric shear for port shear, this method is a small investment, the quality of the cut is also better, but low productivity, labor intensity, and can not cut thicker materials. The use of special rolling shears, this method of high production efficiency, good quality notch. However, this equipment is not universal equipment, manufacturers need to design and manufacture their own. Using air plasma cutting method, this method is simple and easy, the equipment has formed a series, the price is suitable, high production efficiency, but the quality of the cut is not as good as the first two methods, and the cut surface oxide, after cutting the need to use the angle grinding wheel for grinding, metal dust generated in the cutting and grinding process, making the operating environment is very poor. Corrugated pipe in the manufacturing process of inspection, corrugated pipe is allowed to have a slight mold marks, shall not have a large dry steel thickness negative deviation of the scratch, crater or bump uneven; corrugated pipe wave height, wave distance, corrugated total length of the ruler tolerance should be in line with GB1804 Js18 level requirements.

5. Assembly welding of expansion joints

Expansion joint assembly welding process due to the different structure of the expansion joint type, production processes are not the same, but the main processes are bellows and end pipe (or flange) assembly welding – compound expansion joint assembly welding (including guide block or baffle plate and other accessories) – pressure test – assembly or welding of other accessories (such as the inner guide sleeve, jacket, guide rod, pre-stretch rod, etc.) – assembly inspection. Expansion joint in the process of assembly welding should be the following inspection: the dimensional tolerances of the inner and outer diameters of the straight-sided section of the bellows should be in line with the H12 (or h12) level requirements in GB1804; expansion joint and pipe (or equipment) connection flange and end pipe size and technical requirements should be in line with the corresponding standard end pipe connection, both ends of the pipe mouth should be open 30 degrees +/-2.5 degrees of bevel; expansion joint end pipe for the rolled steel plate Electric welded pipe, the end pipe of the external port perimeter tolerance and roundness tolerance should be in line with the relevant provisions; bellows and end pipe (or flange) and other connected ring welding seam should be tungsten ammonia arc welding or melting pole argon arc welding, bellows single wall thickness greater than 2mm can be used arc welding; assembly of the expansion joint should be taken to protect the bellows, to prevent the welding arc burn through the bellows and welding slag splashed on the bellows, the expansion joint parts of the Weld shall not have cracks, porosity, slag and other defects, biting depth shall not be greater than 0.5mm; expansion joint pressure weld after welding, should be pressure weld pressure test, test pressure of 1.5 times the design pressure, according to the volume of the expansion joint size, pressure 10 ~ 30min, check the expansion joint parts have no leakage, the maximum wave distance under pressure and the ratio of the wave distance before pressure does not exceed 1.15; Expansion joint group welding should be the appearance and geometry of the inspection, expansion joint coaxial tolerance of the two ends: when the nominal diameter is less than or equal to 500mm, for 5mm; when the nominal diameter is greater than 500mm, for the nominal diameter of 1%, and less than or equal to 10mm, the two ends of the expansion joint and the main axis vertical tolerance for the nominal diameter of 1%, and less than or equal to 3mm, expansion joint in the factory for pre Pre-stretching, pre-stretching the factory length tolerance should also comply with the provisions of the expansion joint free state length and pre-stretching the factory length are tested.

6. Expansion joint inspection

Inspection items
1) Appearance inspection: visual inspection or surface quality inspection with appropriate magnification.
2) Size inspection: linear size deviation and shape deviation inspection with the required gauges.
3) Weld flaw detection: color penetration flaw detection and radiographic flaw detection.
For Pdesign > 1.6Mpa gas medium expansion joints, Pdesign > 2.5Mpa liquid medium expansion joints, combustible fluid medium expansion joints, toxic fluid medium expansion joints or expansion joints with specific requirements, the outer surface of the longitudinal weld seam of the pipe billet and the accessible inner surface should be 100% coloring flaw detection or 100% ray flaw detection.
For 0.1Mpa <Pdesign ≤ 1.6Mpa gas medium expansion joint or 0.1Mpa <Pdesign ≤ 2.5Mpa liquid medium expansion joint, at least 10% of the longitudinal weld seam of the pipe billet coloring or radiographic flaw and not less than one weld seam.
For Pdesign > 1.6Mpa gas medium expansion joint, Pdesign > 2.5Mpa liquid medium expansion joint, combustible fluid medium expansion joint, toxic fluid medium expansion joint or expansion joint with specific requirements, the bellows should be connected to the ring weld for 100% of the coloring flaw detection.
For 0.1Mpa < Pdesign ≤ 1.6Mpa gas medium expansion joint or 0.1Mpa < Pdesign ≤ 2.5Mpa liquid medium expansion joint, the bellows connection ring weld should be at least 10% of the coloring flaw detection and not less than one weld.
For Pdesign ≤ 0.1Mpa non-combustible fluid media or non-toxic fluid media expansion joint, all welds are allowed without flaw detection.
Pipe billet longitudinal weld defects are allowed to fill once, after forming the bellows defects are not allowed to fill welding. Bellows connected to the ring weld defects allowed to weld twice, the pressure tube section weld defects should not exceed two times.
4) Pressure test: hydraulic test (test pressure of 1.5 times the design pressure) or pneumatic test (test pressure of 1.1 times the design pressure).
Pressure holding time ≥ 10 minutes.
5) Tightness test: kerosene leakage test or gas tightness test.
Gas tightness test pressure is equal to the design pressure, holding time ≥ 10 minutes.
6) Fatigue test: (as the type test items)
Test bellows wave number of not less than three, test displacement cycle rate should be less than 30 cycles/min, the number of cycles according to GB/T12777-1999 specifications, test requirements bellows should not penetrate the wall thickness of the crack.

Expansion joint inspection records

1. Size inspection
Standard requirements. 
The deviation is ±6mm when the size between the outer joint end faces of the expansion joint is >900-3600;
The deviation is ±9mm when the size between the outer joint end faces of the expansion joint is >3600.
2. Welding flaw detection
Standard requirements.
① Before forming the bellows expansion joint should be billet longitudinal weld color penetration flaw detection or ray flaw detection.
② Expansion joint welds should be localized radiographic flaw detection. The length should not be less than 20% of the length of each weld, and not less than 250mm.
③ Bellows expansion joint connection ring weld should be color penetration flaw detection.
3. The pressure test
Standard requirements.
Expansion joint water pressure of 1.5 design pressure resistance performance, there should be no leakage, no obvious deformation, no instability phenomenon.
4. The gas tightness test
Standard requirements.
The experimental pressure is 1.1 times the measured pressure, the expansion joint should have no air leakage.

The manufacture of expansion joints is a complex technology, before the manufacture of the first high-quality design, in the production process must be in accordance with the different scope of application and specific requirements, the strict implementation of the manufacturing process standards, each process must be high standard requirements, in order to avoid the application of industrial production and the adverse impact on the social economy.

Manufacturing Standards for Expansion Joints

European and international Standards

EN 14917*
Metal bellows expansion joints for pressure applications (2009+A1:2012)
This harmonised European Standard specifies the requirements for design, manufacture and installation of metal bellows expansion joints for pressure applications, i.e. maximum allowable pressure greater than 0,5 bar.
Requirements are given for calculation and design of single and multi-ply expansion bellows which may be unreinforced, reinforced or toroidal. They may be subject to internal or external pressure and axial, lateral or angular displacement. Suitable materials and their physical properties are listed.
In addition, information is given on the proper selection and installation of expansion joints in piping and pressure vessel application.
EN 13445-3
Unfired pressure vessels – Part 3: Design (2014/A8:2019)
Part 3 of this harmonised European Standard specifies requirements for the design of unfired pressure vessels covered by EN 13445-1 and constructed of steels in accordance with EN 13445-2. Additional requirements are given for metal bellows expansion joints.
EN 13480-3
Metallic industrial piping. Part 3: Design and calculation (2017)
This part of the European Standard specifies the design and calculation of industrial metallic piping systems, including supports. Additional requirements are given for metal bellows expansion joints (reference to EN 14917).
EN 1736
Refrigerating systems and heat pumps. Flexible pipe elements, vibration isolators, expansion joints and non-metallic tubes – Requirements, design and installation (2008)
This European Standard describes requirements for design and installation of flexible pipe elements.
ASME B31.3

  • Process Piping
  • Appendix X Expansion Joints

The standard specifies requirements for materials, design, fabrication, assembly, erection, examination, inspection, and testing of piping.
Appendix X applies to bellows expansion joints giving requirements for design, manufacturing, and installation of bellows expansion joints.

  • Rules for Construction of Pressure Vessels
  • Division 1, Appendix 26 Bellows Expansion Joints

This division of the ASME Boiler and Pressure Vessel Code provides requirements applicable to the design, fabrication, inspection, testing and certification of pressure vessels operating at either internal or external pressures exceeding 15 psig. Such pressure vessels may be fired or unfired.
Appendix 26 applies to metal bellows expansion joints giving requirements for design, fabrication, examination and testing.
Standard of the Expansion Joint Manufacturers Association, 10th Edition (Errata 2016)
The EJMA Standards apply to metallic bellows expansion joints for piping and pressure equipment. It covers calculation and design of circular and rectangular bellows expansion joints with single or multi-ply bellows that may be unreinforced, reinforced or toroidal. They may be subject to internal or external pressure and axial, lateral or angular displacement.

National Standards

AD 2000 / Merkblatt B 13 (Germany)

  • Single ply bellows expansion joints (2012).
  • Technical rules for pressure equipment.

Calculation basis is given for stresses, spring rates, stability and fatigue cycles of bellows subjected to pressure, temperature, axial, angular or lateral movements.
DIN 30681 (Germany)
Compensators for gas-installations – Expansion joints with stainless steel bellows unit – Safety requirements, testing, marking (2013).
This German Standard describes requirements and testing of non-buried expansion joints with stainless steel bellows up to DN 500 and MOP 16 bar, which are used with gases according to DVGW Arbeitsblatt G 260.
DIN 85031 (Germany)
Ships and marine technology – Steel expansion joints (2014).
This German Standard specifies design, marking, storage, transport, installation, operation and maintenance of steel expansion joints used in piping systems of ships.

How do you install a metal expansion joint?

  • 1) The bellows element shall be protected from damage such as dents, arc strikes, weld spatter, and other damage can cause the joint to fail. ALWAYS protect the bellows element from burn splatter with a flame-retardant cloth or other shielding material. Damage joints are forbidden to be used.
  • 2) Align joint flange and pipe flange holes. Do not try to compensate for flange (flange permit some rotational misalignment) or pipe misalignment by putting any torsional, compressive, extension, or offset loads on the expansion joints. If a bellows is subjected to torsional forces due to hole misalignment, it will reduced cycle life and/or bellows failure can occur. Good practice suggests that a mating flange in the piping system remain unwelded until the expansion joint has been bolted in position.
  • 3) All anchors, guides, and supports must be installed according to engineering drawing and specifications.
  • 4) When expansion joints are fitted with liners or internal sleeves, the unit will be marked with an arrow indicating the direction of flow. So the expansion joints should be installed in the proper orientation according to the direction of flow.
  • 5) Unit lengths must not be altered during installation except for the application of cold pull.
  • 6) Remove shipping restraints after installation, but before hydrotesting.
  • 7) If testing medium is significantly heavier than the product to be carried in the system, care must be taken to support the additional weight.
  • 8) Paints containing low melting point metals or other compounds, particularly aluminum lead or zinc, must not be allowed to come into contact with the bellows convolutions.
  • 9) All installation procedures should conform to E.J.M.A Safety Recommendations in Section B.
  • 10) Expansion joints must be easily accessible to allow for period inspection. Bellows should be inspected for any signs of damage such as dents or scores. Damaged expansion joints should be replaced immediately.   
  • 11) Final System Check – After installation has been completed and shipping bars removed, check all anchors, guides, and pipe supports. Slowly apply test pressure to the system, checking for any unusual movement of the bellows anchors or guides. If irregular movement is observed, immediately lower the pressure and re-examine the system for damage.

Note : Test pressure should not exceed 1-1/2 times of the design pressure. 

Precautions for installation of expansion joint

  • 1. Before installation, the model and specification of the expansion joint of the corrugated compensator and the support configuration of the pipeline shall be checked to meet the design requirements.
  • 2. For expansion joints with lining barrel, it shall be noted that the direction of lining barrel shall be consistent with the flow direction of medium (installed according to the flow direction sign of expansion joint). The hinge rotation screen of the plane angular expansion joint shall be consistent with the displacement plane.
  • 3. For expansion joints that need to be “cold tightened”, the auxiliary components used for pre deformation shall be removed after the expansion joints are pre deformed.
  • 4. After the installation of the pipe system, the auxiliary positioning mechanism and fasteners used for installation and transportation protection on the expansion joint shall be removed immediately, and the limiting device shall be adjusted to the specified position according to the design requirements, so that the pipe system can be fully compensated under the environmental conditions.
  • 5. In addition to the pre deformation of pre tension and compression or “cold tightening” required by the design, it is strictly prohibited to use the method of corrugated pipe deformation to adjust the installation deviation of the pipeline, so as not to affect the normal function of the expansion joint, or it will reduce its service life and increase the load of the pipe system, equipment and supporting members.
  • 6. All moving elements of expansion joints shall not be blocked by external components or restrict the normal action of their moving parts.
  • 7. During installation, welding slag is not allowed to splash on the surface of the corrugated pipe and cause other mechanical damage to the corrugated pipe.
  • 8. For expansion joints and their connecting pipes used for gas medium, when conducting hydrostatic test, it is necessary to consider whether it is necessary to add temporary supports to the connecting pipes of expansion joints to bear the weight during water filling.
  • 9. The water for hydrostatic test shall be pure and non corrosive, and the content of chloride ion in the water shall not exceed 25ppm. After the hydrostatic test, the accumulated water in the bellows shall be drained as soon as possible, and the inner surface of the corrugated shell shall be blown dry rapidly.
  • 10. The neutrality of the pipeline is better. If there is no other method to ensure it, the method of cutting off equal length pipes after laying straight pipes and then installing expansion joints can be used to ensure it.
  • 11. It must be noted that the expansion joint does not absorb torque, so it is not allowed to be twisted when installing the expansion joint.
  • 12. All moving elements of the expansion joint shall not be stuck by external components or restrict the normal operation of its moving parts.
  • 13. The thermal insulation layer shall be made on the outer protective sleeve of the expansion joint, not directly on the corrugated pipe. Chlorine containing insulation materials shall not be used.
  • 14. During installation, welding slag is not allowed to splash on the surface of the bellows and cause other mechanical damage to the bellows.
  • 15. The support must meet the design requirements. It is strictly forbidden to test the pressure in the pipeline before the support is installed, so as to avoid damaging the expansion joint.
  • 16. The expansion joint is allowed to be tested under 1.5 times of the nominal system pressure.
  • 17. During the operation of pipelines equipped with expansion joints, the valves shall be opened and closed gradually to avoid sudden changes in temperature and pressure in the pipelines, which may damage the supports or expansion joints.

Under what conditions does the expansion joint fail and need to be replaced?

Expansion joints are widely used in pipelines, including rubber expansion joints and metal expansion joints. The expansion joints need to be replaced after a period of time. Under what circumstances do they need to be replaced? Today, we will discuss the causes of failure of rubber expansion joints.
When the expansion joint fails, there are obvious warning signs:

  • 1. The arch inversion indicates that the system vacuum has exceeded the expansion value specified by the joint.
  • 2. Cracking at the bottom of the arch indicates that the joint has been excessively stretched, and it should be replaced with one of appropriate length.
  • 3. Layer separation outside the cover. This indicates that the joint has moved too much.
  • 4. Leakage caused by excessive expansion, mating flange surface problems or improper installation, especially (but not limited to) bolt fastening.
  • 5. Arch balloon, indicating excessive system pressure.

In this case, the expansion joint may burst, which is very common because most joints are designed with a safety factor of 3:1 or 4:1, and the bursting pressure exceeds 1000psi. However, it is easy to ignore the difference between the current and original state of the expansion joint.
For example, in the general water supply service with relatively low flow, stable environment and temperature, stable system pressure and minimal movement, expansion joints can theoretically last up to 20 years. However, it can also be used in other aspects, such as flue gas desulfurization system, to pump highly abrasive slurry medium at high flow rate to accelerate joint wear. Each application environment is different, so the root cause of invalid expansion joints must be removed.
In general, the expansion joint is damaged and fails from the inside, and the flow conditions will have a negative impact on the entire assembly.
Among the three basic components of the expansion joint, the tube is the most critical, because it acts as the physical and chemical boundary between the body and the media. If the tube is damaged, the body may be exposed to the medium, leading to possible degradation.
This is why it is essential to keep an eye on any inspection of the failed expansion joint. In grinding applications, the medium can be worn through the main body of the pipe and joint to the point where only the minimum amount of pressure can cause the pipe to leak or burst. In other cases, too high a temperature may cause the tube to harden. This in turn causes the tube to lose its elasticity and crack under dynamic motion.
Understanding the root cause of expansion joint failure can provide useful information about the system in which they are installed, but it is best to prevent this from happening first. At present, the main problem is to formulate and deploy maintenance plans, analyze and prevent potential risks that can make expansion joints fail, and take necessary preventive measures. The frequency of inspection varies depending on the application conditions. Critical paths and high-risk systems may need to be checked quite frequently, while less important systems can be checked semi annually or even annually.
These are the conditions shared by everyone that cause the expansion joint to fail and need to be replaced, depending on the situation during use.

Why is the expansion joint in operation suddenly broken?

  • 1. The reason that first led to the rupture was that the expansion joint was used up after a long time of use.
  • 2. The second problem is the material, because the expansion joint needs metal material. If there is no problem in all aspects of the operation but it suddenly breaks, it is because the material is too poor.
  • 3. Being in the pipeline for a long time, the long-term passage of some corrosive medium is also the reason why the expansion joint will burst suddenly.
  • 4. If we did not do a good job in regular repair and maintenance of the expansion joint, it is also the reason for the sudden phenomenon.
  • 5. The expansion joint shall be correctly installed and operated.

What should we pay attention to when replacing metal expansion joints?

What should be paid attention to when the expansion joint is replaced when it reaches the service life? The expansion joint is a kind of compensation element, which mainly uses the effective expansion and deformation of the bellows of its main body to absorb the size changes of pipelines, conduits, containers, etc. caused by thermal expansion and cold contraction. The use of corrugated compensator should adapt to various working conditions, so the materials of expansion joints are diverse. For example, stainless steel corrugated expansion joints, non-metallic corrugated expansion joints, PTFE corrugated expansion joints, rubber corrugated expansion joints, etc., the service life of expansion joints shall be deduced according to the working conditions. For example, various parameters such as fatigue number, working condition temperature and corrosivity indicate that the ripple compensator has a certain service life. Then, what should be paid attention to when the expansion joint reaches its service life?
After the expansion joint reaches its service life, its material will have different degrees of aging, oxidation or fatigue. In this case, it is not suitable to continue to use, and a new corrugated compensator should be replaced in time.
Attention shall be paid to the replacement of expansion joint:

  • Find relevant original data. According to the model, pressure, connection method and compensation amount of the corrugated compensator recorded in the original data, determine the actual total installed length of the corrugated expansion joint.
  • If there is no relevant original data, in this case, the transmission medium, design pressure, total length, etc. of the corrugated compensator shall be determined, and photos shall be taken and provided to the manufacturer. If the compensation amount of the expansion joint cannot be determined, the temperature of the transmission medium and the distance between the two expansion joints shall be provided.

Corrugated expansion joints sometimes pull off during actual work, which will damage the universal corrugated expansion joints and seriously threaten the entire pipeline. If they are damaged, it has a lot to do with the installation of fixed supports in the pipeline.
Why does the expansion joint pull off?
After installation, the expansion joint needs to adjust the pull rod device attached to the metal compensator to its compensation range instead of removing all devices.
It is unnecessary to set the fixed pipe support for the pipeline during the pressure test. If the pipe support is not set, the stainless steel metal expansion joint will extend infinitely to its own limit with the pressure and impact force during the pressure test. At this time, the expansion joint has been stretched into a straight cylinder or lost its expansion performance.
Why is the degree of damage closely related to the fixed pipe rack?
First of all, it has been pointed out that if the fixed pipe rack is set in strict accordance with the requirements during the installation, the stainless steel corrugated pipe, even under the influence of the pipe pressure and thrust when the pull rod device is removed, can only cause the water treatment metal expansion joint in the pipe rack to be pulled off and twist or offset, without damaging the equipment and pipelines of other pipe sections.
How to prevent the stainless steel corrugated pipe from pulling off, and how to set the fixed pipe rack?
A good installation method is to fix the limit bolt within the scope of expansion compensation for the water treatment unrestricted corrugated expansion joint with a pull rod device during installation. Another point that must be noted is that the fixed pipe support and bracket must be set to ensure that the pipeline will not be displaced while being subjected to transient pressure and thrust, so that the expansion joint can play its major role.

How thick is an expansion joint?

Stainless steel bellows compensator of the main components of the bellows belongs to the thin-walled nature, the selection of bellows wall thickness is required to combine the medium and compensation volume and other parameters to determine, and not wall thickness will be durable.
In the working condition of the stainless steel bellows compensator needs to absorb the displacement of the pipeline in the state of pressure. Its main component bellows to have a high pressure-bearing capacity, in order to make the bellows compensator in a limited length to get a larger amount of deflection, the need to choose the wall thickness, the thinner the wall thickness the better.
Usually choose the wall thickness to consider the pressure range compensation displacement requirements and pressure-bearing capacity. The choice of wall thickness of the three is to form a contradictory demand. In order to achieve the amount of compensation and to be able to pressure requirements, the compensator manufacturers will design the bellows into a thin-walled multi-layer structure, the shape of the equivalent of a closed spring. In the working state of the stainless steel bellows compensator stress is generally composed of pressure stress and displacement stress, the same need to consider when selecting the wall thickness of the strength of the pressure, bearing alternating flexural deformation under the fatigue life of the bellows and deformation coordination.
If the medium contains corrosive, consider the working pressure at the same time also take into account the material and the medium match to avoid corrosion. Combined with computer software through the working pressure combined with the compensation amount of the bellows wall thickness and the number of corrugated waves to calculate. From raw materials, stainless steel bellows compensator billet welding and forming, structural components and end pipe flange welding and other process control, to keep a good link.

How is the price of stainless steel bellows compensator set?

The larger the compensation volume, the higher the price? This statement is correct, but the premise is the same model and specification. In this case, the larger the compensation volume of stainless steel bellows compensator, the higher the price will increase.
In communication with the customer, the customer raised a question: the same size of stainless steel bellows compensator, but the need to compensate the displacement is different, so the price is the same?
The compensation amount is the pipeline media due to thermal expansion and contraction of temperature changes in the axial, lateral or angular displacement.
According to the compensation amount to calculate the number of corrugations of stainless steel bellows compensator. The larger the compensation, the more the number of corrugations calculated, the more materials will be used, and the price is slightly higher compared to the compensation volume of small.
Therefore, the same size of stainless steel bellows compensator, the need to compensate for different compensation, which also causes the price of two stainless steel bellows compensator is not the same. When the larger the compensation amount, the higher the price, on the contrary, the smaller the compensation amount, the lower the price. How to know the price of stainless steel bellows compensator? This requires you to provide the size of the pipe, working pressure, medium and medium temperature, connection mode, installation form and compensation amount of these technical parameters.
If the compensation amount of stainless steel bellows compensator is not calculated correctly or the purchased product does not meet the requirements of the pipeline for the compensation amount, it will damage the stainless steel bellows compensator.

Metal bellows compensator VS metal hose

Metal bellows compensator and metal hose are bellows as the core component of the pipeline fittings for the transport of various fluids, the nature of its work is in the pipeline and pipeline, pipeline and equipment, equipment and equipment between the connection to play a compensatory role. Therefore, people often confuse the metal bellows compensator with metal hose. In fact, they have some differences in the working principle. Metal bellows compensator and metal hose in some occasions can not be used in place of each other, unreasonable design will not be able to get the desired compensation effect.
Metal bellows compensator without metal wire or metal belt woven mesh sleeve on the outer surface, metal bellows compensator is equipped with tie rods, hinges, strengthening rings and other restraint devices, is the ratio of less than 3 ring bellows assembly. Metal bellows compensator in the western countries are used to call it metal bellows compensator. In general, the metal bellows compensator to its axial expansion or angle change than to compensate the pipeline system due to temperature differences caused by the position of the movement; to absorb the equipment open, stop or normal operating conditions of vibration.
Metal hose mainly refers to a kind of spiral bellows, for a flexible pressure-resistant pipe fittings installed in the liquid conveying system, to compensate for mutual displacement of the pipeline or machine, equipment connection end, absorb vibration energy, can play a role in vibration damping, sound dissipation, etc., with good flexibility, light quality, corrosion resistance, fatigue resistance, high and low temperature resistance, flexible between the pitch, a good expansion and contraction, no blockage and stiffness, etc.

How to order stainless steel bellows compensator?

When customers order stainless steel bellows compensator with special requirements, the following points must be provided in the order contract.

  • 1. Structure length.
  • 2. Connection form.
  • 3. Nominal diameter, full diameter, reducer, pipe diameter.

As the sales of stainless steel bellows compensators vary from model category to model category, the factory can custom design special products according to the special requirements of customers.
If the customer provides a certain product type and model, the customer should correctly explain the meaning and requirements of the product model, and sign a contract with mutual understanding and agreement.

How to find a suitable expansion joint manufacturer?

Metal expansion joints are widely used in industry, but how to choose a suitable one is an important question. In this article, we will share some insights on how to choose the right metal expansion joint manufacturer and the application of metal expansion joints.

When to choose a suitable metal expansion joint?

You should choose a suitable metal expansion joint when the temperature is too low. If the temperature is lower than -40℃, you need to use stainless steel as your material. In addition, if you want to use a metal expansion joint in an environment with high humidity or salt spray, we recommend using 316L stainless steel.

When choosing a metal expansion joint for hot water and steam pipelines, you should pay attention to whether it can be used in high-temperature conditions: the maximum operating temperature of 304L stainless steel is 80℃ or less; for 316L stainless steel,it’s 150℃ or less (the allowable service life of 304L±45mm×90mm×30mm×2m long welded stainless steel pipe).

What is the application of metal expansion joints?

As the pipeline system is made up of a series of steel pipes and fittings, it is very important to ensure that the pipeline system can perform its function safely and effectively. Metal expansion joints are used in the pipeline system to prevent damage and leakage. The metal expansion joint is an important component of a pipeline system, which has many different uses:

  • To prevent stress concentration on the end face when connecting two tubes together, causing cracking or even rupture;

  • To resist external pressure caused by earthquakes and other natural disasters;

  • To resist thermal expansion and contraction caused by changes in temperature;

  • To resist internal pressure caused by fluid flow through pipelines (eg diesel fuel).

How to calculate the power for metal expansion joints?

The power of metal expansion joints is mainly calculated by the bending stress, which depends on the material and the bending radius. For example, if you use AISI304 stainless steel, it has a Young’s modulus of about 210GPa, and its tensile strength is about 758MPa. If you use 18mm diameter, 20mm long steel pipe as an example to calculate:

  • Bending radius = R = 2 * 180 * pi / 6 = 132mm (approximate)

  • Power: Fb (bending force): Pb = Kb * Fb= Kb * Mpa/longitudinal section area=2.1*4500/(132*38)=108kNm/m or 0.0108MN/m or 108kN-m/meter or 108KNM per meter

  • You can see that power consumption is greater than 1MN/M

Metal expansion joints are widely used in industry, but how to choose a suitable one is an important question.

When choosing a metal expansion joint, it is not only important to consider the quality of the product, but also the selection of manufacturers.

Finding someone who can design and manufacture expansion joints is not as simple as you might think. You’ll need to consider many factors before you commit to your supplier: business background, product type, design and manufacture standards, manufacturing process, delivery time after-sales support lead time. Here are some things to consider when looking for an expansion joint manufacturer:

Business background

A good expansion joint manufacturer will have a history of successful operations. This is a business that has been around for some time, not one that just popped up and is hoping to sell you something. To know whether your potential supplier is established, you can ask for references from current customers or search online for reviews. A company with an established reputation will have few complaints about its products or services, while one that has recently entered the market may be struggling to establish itself as reliable and trustworthy.

In addition to demonstrating proven longevity, an expansion joint manufacturer should also have stable finances and prove their ability to pay suppliers on time (if they’re dealing with internal supplies) or pay their employees regularly (if they provide employment). If this seems like too much work for you when looking at companies’ websites—or if you’d rather just skip right over it altogether—you can simply check out their annual report on the stock market; larger companies will be required by law to publish these documents every year (though smaller businesses are not).

Product type

The type of product you choose will depend on your application and budget. Expansion joints can be made from many different materials, including:

  • Rubber (thermoplastic or natural)

  • Stainless steel

  • Copper

Each material has its pros and cons, so it’s important to consider what is most suitable for your particular project. For example, if you have a tight budget but don’t need a long lifespan, rubber is the best choice because it’s relatively inexpensive and durable. However if longevity is important but not cost, stainless steel may be a better option since it lasts longer than rubber at an increased price point.

Design and manufacture standards

  • Design standards.

How thick should it be? What kind of material should it be made out of? Is the expansion joint flexible enough to accommodate movement in the structure, or will it crack and break off like a brittle stick if installed incorrectly? These are all questions you’ll have to ask your manufacturer when designing a suitable expansion joint, but they’re not all that’s involved here.

  • Manufacturing standards.

Even if your design is perfect and has been put through rigorous testing by third-party engineers, there’s still room for error when manufacturing the product itself—and that has less to do with what goes into making an expansion joint than how well those parts fit together after assembly.

  • Testing standards.

Even if everything was built perfectly according to plan (and did I mention this was rare?), there are still tests that need to be run before you begin installing any new part into your building or structure: load tests; hydrostatic pressure tests; thermal cycling tests; just name it! And don’t forget about visual inspection either: if something doesn’t look like its supposed too then chances are something went wrong somewhere along the line during production or transportation from factory floor…

Manufacturing process

Once you have chosen the right expansion joint manufacturer, it’s time to find out more about their manufacturing processes. This way, you can be sure that they will follow industry standards and produce quality products.

The fabrication process involves many steps and materials depending on your application. For example:

  • Steel is commonly used as a base material because it offers high strength and corrosion resistance, but other materials are also available (e.g., stainless steel alloy).

  • Rubber is used for exceptional durability at high temperatures and in harsh environments.

  • Plastic components offer good protection against UV radiation as well as good dimensional stability under fluctuating temperatures; however, they tend to be less reliable than rubber due to lower tensile strength.*

Delivery time

  • Delivery time: This is the amount of time between when you place your order and when the product arrives at its destination.

  • Quote turnaround time: How long it takes to get a quote from the manufacturer. A short turnaround time means that you can get an estimate faster, which helps you plan your budget and schedules better.

  • Sample lead-time: The period of time between placing an order for samples (or a sample kit) and receiving them in hand.

After-sales support

  • You should be able to find a manufacturer that offers after-sales support.

  • They should be able to provide spare parts and technical support when needed.

Lead time

Before you even begin to shop for a contractor, it’s important to understand the concept of lead time. Lead time is the period between when you place an order and when that order is delivered. The length of this period depends on several factors:

  • How complex your project is

  • How big your order is (if it’s small enough, you may be able to get away with having multiple shipments)

Lead time can have a significant impact on your schedule if you’re operating under a deadline or if there are other factors affecting when and how quickly work needs to be performed.

Here are some things to consider when you’re looking for a expansion joint manufacturer

It is important that the expansion joint manufacturer can meet your exact requirements. The following questions should help you evaluate whether or not a potential expansion joint supplier is right for your project:

  • Is the business background of the company (its history) relevant?

  • What types of products does it manufacture? Does this manufacturer have experience in producing similar products as yours? If so, how long has the company been producing these products and does it have excellent quality control processes in place to ensure consistent product quality?

  • How do they design and manufacture their expansion joints, are there any specific standards that they follow during design and manufacturing processes? Do they use an automated production process or handcrafting method to create their expansion joints; if so, which one! Are there any special certifications needed before being eligible to produce a specific type of expansion joint; if yes, who provides these certifications?

  • How long will it take them deliver on time upon receipt of payment at their end?


In summary, it’s important to do your research before selecting an expansion joint manufacturer. You should consider their experience and reputation in the industry, as well as their product quality and manufacturing standards.

Source: China Expansion Joints Manufacturer – Yaang Pipe Industry Co., Limited (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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

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