Analysis on the failure and leakage of sealing gasket in petrochemical plant
What is sealing gasket?
Sealing gasket is a kind of auxiliary material which is often used in mechanical device. It can increase the sealing property of the connection port of mechanical device and stabilize the connection port. It plays an important role in the mechanical installation. Taking the sealing gasket in petrochemical plant as an example, this paper focuses on the practical selection method and the causes of failure and leakage, so as to give full play to the auxiliary role of materials and reduce the loss in chemical production.
Petrochemical plant is the basic part of comprehensive development and application of petroleum materials. With the gradual expansion of China’s petrochemical production scope, the quality and work efficiency of petrochemical plant materials are more and more concerned by the society. The research shows that strengthening the quality management of sealing gasket in petrochemical plant is helpful to reduce the loss in petroleum production and prolong the service life of chemical production device. The selection of sealing gasket in petrochemical plant and the cause of its failure and leakage are of great importance to the development of modern industry Oil production efficiency occupies a prominent position.
Sealing mechanism of sealing gasket design
Flange, gasket and bolt are common auxiliary materials in petroleum equipment. Among them, the flange is the elastic barrier groove in the processing of petroleum equipment, which is mainly responsible for providing a small bag of guiding channel for the liquid when the liquid is injected into the oil device. The gasket is a part of the overall connection structure. The interval between the flange and the bolt can be adjusted, and the length, width and material of the gasket can be adjusted according to the actual needs of the flange and bolt.
If the flange, gasket and bolt in petrochemical plant are regarded as a whole, then the flange and bolt are the external covering structure supporting the whole, and the gasket is the connecting part of the whole. Therefore, the sealing gasket is the core structure to ensure the petrochemical plant, which directly determines the overall work effect of the petrochemical plant.
Type and selection of sealing gasket in petrochemical plant
Nonmetal gasket is more common and widely used in modern chemical plant. It includes rubber gasket, polytetrafluoroethylene gasket and graphite gasket.
- Rubber gasket. This kind of gasket is mainly made of rubber. The gasket is made of silicone rubber, nitrile rubber and other materials with good sealing performance. It has the characteristics of good sealing performance and high flexibility. In the process of actual chemical production and application, rubber gasket can effectively solve the problem of poor sealing performance of equipment materials in practical application, so as to increase the sealing degree.
- PTFE gasket. It is a gasket material with ethylene material as the external protective layer. On the basis of covering tightness of rubber gasket surface, the glossiness and smoothness of gasket surface layer are increased to ensure the elastic rate of rubber gasket. If the materials used in chemical plant need to choose the material with high thickness and smooth surface as sealing gasket, PTFE gasket can be the preferred material.
- Graphite gasket. It is a kind of gasket made of graphite raw material processed at high temperature. The chemical plant material made of graphite can not only meet the characteristics of good flexibility and strong heating capacity, but also have high chemical molecular stability. When the gasket is used in practice, the probability of gasket oxidation and corrosion in the connection device is low. In order to realize the high-quality utilization of chemical gasket resources during modern chemical production, this kind of gasket can be selected in chemical plants with strong corrosivity in chemical production.
The above analysis and exploration on the practical application conditions of the three gaskets not only give some inspiration to the chemical production, but also provide an effective method for the continuous optimization and selection of materials in the modern chemical processing process.
- (1) Metal clad gasket and its selection. Metal clad gasket is a kind of metal gasket of sealing gasket in petrochemical plant. The metal material is mainly concentrated in the shell part. The advantages of this kind of gasket are mainly reflected in four aspects: high temperature resistance, corrosion resistance, compression resistance and good sealing performance. However, in the long-term use, the gasket is easy to lose elasticity, and the recovery performance is poor. If the selection is unreasonable, the service life of the gasket will be significantly shortened. With the extension of service time, the sealing effect can gradually decline. In order to improve the sealing level of gasket and prevent failure leakage, it is suggested to evaluate the straightness of flange and smoothness of bolt during the selection of gasket. It is found that compared with smooth bolt, corrugated bolt has stronger elasticity and higher sealing efficiency. Therefore, it is suggested that the metal clad gasket composed of corrugated bolts should be preferred to improve the sealing level of petrochemical plants.
- (2) Tooth shape combination gasket and its selection. The metal material of toothed composite gasket is generally located in the gasket core. The metal core of this type of gasket is mostly tooth shaped and covered with graphite. The practical experience shows that the pressure that the toothed combination gasket can bear is 6.3 ~ 15MPa. When the operating temperature of petrochemical plant is less than or equal to 650 ℃, this type of gasket has no deformation risk and has high temperature tolerance. The advantage of the toothed combination gasket lies in good sealing performance, but a thin layer of 0.10 ~ 0.15cm should be left during installation to avoid exposure of metal tooth tip. Lack of elasticity is the main defect of this kind of gasket. A sudden change in the operating pressure of a petrochemical unit may also occur due to the lack of flexibility of the gasket. If it is necessary to select this kind of gasket for petrochemical plant, the stable operation environment must be ensured to avoid leakage.
- (3) Corrugated composite gasket and its selection. The metal material of corrugated tooth composite gasket is located in the skeleton. The metal framework of the gasket mostly contains concentric grooves. Therefore, compared with the metal clad gasket and the tooth shaped composite gasket, the corrugated tooth composite gasket has stronger elasticity. Excluding the influence of other factors, the service life of the gasket is usually longer. In addition, due to the tight connection between the ring tooth peak and the flange face of the gasket metal framework, the sealing property of the material is often strong. During the operation of petrochemical plant, the pressure of gasket is higher. Under the influence of high pressure, graphite material is easy to lose. When the corrugated tooth composite gasket is applied to the sealing process of the device, the closed annular tooth peak and flange face can block the loss process of graphite material, thus reducing the risk of “crushing” and “scattering”, improving the safety of gasket use and preventing failure leakage. In view of the above advantages, it is suggested that corrugated composite gasket should be used in petrochemical industry.
- (4) Spiral wound gasket and its selection. Spiral wound gasket is a common type of gasket in petrochemical industry. The advantages of this kind of gasket are mainly reflected in “strong elasticity”, “high strength”, “good pressure absorption effect” and “high temperature resistance”. The vibration, high temperature and high pressure produced during the operation of petrochemical plant have little influence on gasket performance. The main defects of spiral wound gasket are “instability” and “scattered”. The cause of “instability” is related to the stress characteristics of gasket. Under the influence of axial force, the gasket can be damaged by pulling off. If the pressure on the filler is transmitted to the inner steel strip along the inner diameter, it will also cause the instability problem and lead to the gasket sealing failure. If the spiral wound gasket is needed in petrochemical industry, it is suggested to reduce the low pressure tightening force and prolong the service life of the gasket.
Causes and solutions of seal gasket failure and leakage in petrochemical plant
(1) Improper operating parameters of sealing gasket. When there is a large error in the manufacturing parameters of sealing gasket in petrochemical plant, the value of gasket between flange and nut will be greatly reduced, which will lead to the reduction of sealing range of gasket when the nut rotates, which will affect the sealing effect of petrochemical plant.
In order to solve this problem, the sealing gasket can be sheared along the outer edge of the flange structure when adjusting the operation size of the sealing gasket, so as to ensure that the sealing gasket still keeps a good sealing relationship with the external structure of the petrochemical device after the bolt is fixed. At the same time, during the bolt rotation, the gasket position should be avoided to change with the change of the bolt position, so as to reduce the displacement of the gasket during the bolt adjustment. For example, the flange outer edge is 10 mm and the bolt length is 5 mm in a chemical plant. When the gasket is treated, it should be controlled to 10 ~ 13mm, so that the failure of the gasket will not occur when the bolt is used to fix the gasket.
(2) The performance of the gasket is damaged. The damage of gasket performance is also one of the factors leading to the failure of chemical plant.
- ① Metal or non-metallic gasket structure in the oxidation, strong acid corrosion environment, gasket corrosion or oxidation. If the gasket used in chemical plant is damaged material, the gasket can not play a role in practical application.
- ② The thickness uniformity of the gasket itself is not enough. In practical application, due to the difference of the roughness of the gasket, the application failure of the gasket will occur.
In order to avoid the failure of gasket in the application of chemical plant, the problem can be solved by strengthening the performance protection of gasket:
- ① during the practical application of chemical production device, try to avoid sealing gasket in strong high temperature, low temperature, strong acid and strong alkali environment.
- ② In the practical application of sealing gasket, the gasket with uniform geology and high quality should be selected as auxiliary material. For example, when the gasket is used for processing production in a chemical industrial production device, the production personnel shall first select the gasket structure conforming to the standard according to the general requirements of chemical production, and take the gasket material of upper quality as the first choice.
- ③ During the installation of flange, gasket and nut, try to avoid being in the installation environment of high temperature and strong corrosivity, and then install the gasket according to relevant conditions.
(3) The flange stiffness is large. The higher flange stiffness will result in the loss of original function of sealing gasket in chemical plant, which is caused by the mismatch between flange structure and gasket structure in chemical plant. Therefore, the sealing gasket with moderate flange stiffness and common in actual production should be taken as the first choice during the subsequent treatment of chemical plant. Such as rubber gasket, graphite gasket
Soft materials such as tablets can be used as the preferred materials at this time.
To sum up, the selection of sealing gasket in petrochemical plant and the cause of failure and leakage are the theoretical induction of comprehensive development and application of modern chemical production machinery resources. In this paper, through the common gasket types and application selection, the problems of improper operation parameters, gasket performance damage, flange stiffness are analyzed.
Author: Zhou Feng
Source: China Gaskets 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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