Inspection and testing
The strength or hydraulic test, sealing test and necessary non-destructive test of the valve are necessary conditions to measure whether the valve is qualified, but they are not sufficient conditions to measure the quality of a valve. At least for high-pressure hydrogenation valves, they can't completely reflect the comprehensive quality of a hydrogenation valve. Take the valve's sealing as an example. Generally, as long as the machining accuracy of the sealing element is ensured, it is easy to pass the sealing test in the cold state in the factory. However, it does not mean that the valve can maintain a good seal under the conditions of being used for a long time, especially in high-temperature and high-pressure working conditions. Once wear, corrosion, stress relaxation, deformation and material degeneration and other problems occur for the valve parts, the sealing performance of the valve will be affected, and in severe cases, the sealing will fail. The stability and uniformity of the metal structure of the component and the partial stress level caused by the component's structure will affect the corrosion, stress relaxation, deformation and degeneration of the material to some extent. However, these problems of materials cannot be checked by non-destructive testing and pressure testing under cold states.
For low and medium pressure valves used for general media, the above-mentioned problems may not exist or are not prominent. For valves used under high-pressure hydrogenation conditions, these problems should not be neglected. Therefore, valves for high-pressure hydrogenation should be subjected to a complete set of tests. Because the material's quality of the pressure-bearing parts of the valve, especially the casting material has a great impact on the service life of the valve, further discussion will be had on the tests of pressure-bearing castings.
The quality of the casting's material mainly depends on its manufacturing processes such as smelting processes and manufacturing processes. Various inspection tests on its products are only a means of evaluating its quality, and it cannot change the quality of the material. Therefore, it is particularly important to conduct a systematic and scientific process assessment of valve parts before starting industrial production. The quality orientation in the process evaluation directly determines the quality of the material (product). Combined with the characteristics of media of the high-pressure hydrogenation unit, the process evaluation items for its main pressure-bearing parts before industrial production are proposed as follows:
① Visual inspection should be carried out according to the items listed in MSSSP-55.
② The analysis of the chemical composition includes on-the-spot analysis and product analysis, especially the analysis of harmful impurity elements such as sulfur, phosphorus, arsenic, antimony, hydrogen and ammonia. The analysis of the chemical composition should be performed in accordance with the corresponding ASTM standards.
③ Mechanical performance tests include tensile tests, bending tests, impact tests and hardness tests. At the same time, perform the tensile strength, yield strength, elongation and section shrinkage rates, and conduct the fracture analysis. The mechanical performance tests shall be carried out in accordance with the corresponding ASTM standard.
④ Macroscopic organization inspection includes the inspection of defects such as gas holes, cracks, porosity, slags, big non-metallic inclusions, and sulfur and phosphorus segregation. The inspection should be carried out in accordance with ASTME381 and other standards.
⑤ Microstructure inspection includes the inspection of segregation, strip structure, dendritic structure, grain sizes, small non-metallic inclusions and other defects. For austenitic materials, the checking of ferrite content shall also be included. The inspection is carried out in accordance with ASTM 38l/E45/E112 and other standards.
⑥ Non-destructive inspection includes RT, UT, MT, PT and other inspections. Provide the criteria of appropriate acceptance and qualification rates. Non-destructive inspection should be carried out according to MSS SP-54, ASTM A388, ASTM A275, ASTM B165 (Practice B) standards.
⑦ Intergranular corrosion tests are only required for austenitic stainless steel. They should be conducted according to ASTME262 (Practice E) standard.
⑧ Welding performance tests include tensile, bending, impact, hardness and non-destructive tests.
⑨ The bursting test of the valve body: the burst test for the liquid should be carried out in accordance with the ANSI B31.2 standard. In the case of meeting certain requirements, the process parameters determined through process evaluation can be used as production parameters and they should be strictly implemented in industrial production to obtain high-quality valves that meet the high-pressure hydrogen application conditions.
Quality Control
The quality problems of Chinese valves are caused by management, because many manufacturers in China do not have a specific and feasible operating procedure for each process of product manufacturing. Even if there is such a procedure, there is no guarantee that every worker will follow the procedure 100%, which leads to the Chinese valves not being as good as foreign valves. At present, most domestic valve factories have obtained the quality certification of ISO 9000, which strengthens the quality management in the manufacturing process of valves to some extent. However, we must also pay attention to the establishment of technical documents, because the advanced product mainly depends on the advanced technical documents.
Conclusion
Many factors affect the quality of valves. We must do well in all aspects to produce high-quality valves. In the age of information, valve manufacturers should also go abroad, communicate more with the outside world and users, including engineering design departments. Understand the needs of the customer and working conditions of the valve's medium. Only in this way can we produce suitable valves and build the market. Communicate with foreign valve manufacturers to learn about advanced technologies and new products, and use them to improve our products.
The strength or hydraulic test, sealing test and necessary non-destructive test of the valve are necessary conditions to measure whether the valve is qualified, but they are not sufficient conditions to measure the quality of a valve. At least for high-pressure hydrogenation valves, they can't completely reflect the comprehensive quality of a hydrogenation valve. Take the valve's sealing as an example. Generally, as long as the machining accuracy of the sealing element is ensured, it is easy to pass the sealing test in the cold state in the factory. However, it does not mean that the valve can maintain a good seal under the conditions of being used for a long time, especially in high-temperature and high-pressure working conditions. Once wear, corrosion, stress relaxation, deformation and material degeneration and other problems occur for the valve parts, the sealing performance of the valve will be affected, and in severe cases, the sealing will fail. The stability and uniformity of the metal structure of the component and the partial stress level caused by the component's structure will affect the corrosion, stress relaxation, deformation and degeneration of the material to some extent. However, these problems of materials cannot be checked by non-destructive testing and pressure testing under cold states.
For low and medium pressure valves used for general media, the above-mentioned problems may not exist or are not prominent. For valves used under high-pressure hydrogenation conditions, these problems should not be neglected. Therefore, valves for high-pressure hydrogenation should be subjected to a complete set of tests. Because the material's quality of the pressure-bearing parts of the valve, especially the casting material has a great impact on the service life of the valve, further discussion will be had on the tests of pressure-bearing castings.
The quality of the casting's material mainly depends on its manufacturing processes such as smelting processes and manufacturing processes. Various inspection tests on its products are only a means of evaluating its quality, and it cannot change the quality of the material. Therefore, it is particularly important to conduct a systematic and scientific process assessment of valve parts before starting industrial production. The quality orientation in the process evaluation directly determines the quality of the material (product). Combined with the characteristics of media of the high-pressure hydrogenation unit, the process evaluation items for its main pressure-bearing parts before industrial production are proposed as follows:
① Visual inspection should be carried out according to the items listed in MSSSP-55.
② The analysis of the chemical composition includes on-the-spot analysis and product analysis, especially the analysis of harmful impurity elements such as sulfur, phosphorus, arsenic, antimony, hydrogen and ammonia. The analysis of the chemical composition should be performed in accordance with the corresponding ASTM standards.
③ Mechanical performance tests include tensile tests, bending tests, impact tests and hardness tests. At the same time, perform the tensile strength, yield strength, elongation and section shrinkage rates, and conduct the fracture analysis. The mechanical performance tests shall be carried out in accordance with the corresponding ASTM standard.
④ Macroscopic organization inspection includes the inspection of defects such as gas holes, cracks, porosity, slags, big non-metallic inclusions, and sulfur and phosphorus segregation. The inspection should be carried out in accordance with ASTME381 and other standards.
⑤ Microstructure inspection includes the inspection of segregation, strip structure, dendritic structure, grain sizes, small non-metallic inclusions and other defects. For austenitic materials, the checking of ferrite content shall also be included. The inspection is carried out in accordance with ASTM 38l/E45/E112 and other standards.
⑥ Non-destructive inspection includes RT, UT, MT, PT and other inspections. Provide the criteria of appropriate acceptance and qualification rates. Non-destructive inspection should be carried out according to MSS SP-54, ASTM A388, ASTM A275, ASTM B165 (Practice B) standards.
⑦ Intergranular corrosion tests are only required for austenitic stainless steel. They should be conducted according to ASTME262 (Practice E) standard.
⑧ Welding performance tests include tensile, bending, impact, hardness and non-destructive tests.
⑨ The bursting test of the valve body: the burst test for the liquid should be carried out in accordance with the ANSI B31.2 standard. In the case of meeting certain requirements, the process parameters determined through process evaluation can be used as production parameters and they should be strictly implemented in industrial production to obtain high-quality valves that meet the high-pressure hydrogen application conditions.
Quality Control
The quality problems of Chinese valves are caused by management, because many manufacturers in China do not have a specific and feasible operating procedure for each process of product manufacturing. Even if there is such a procedure, there is no guarantee that every worker will follow the procedure 100%, which leads to the Chinese valves not being as good as foreign valves. At present, most domestic valve factories have obtained the quality certification of ISO 9000, which strengthens the quality management in the manufacturing process of valves to some extent. However, we must also pay attention to the establishment of technical documents, because the advanced product mainly depends on the advanced technical documents.
Conclusion
Many factors affect the quality of valves. We must do well in all aspects to produce high-quality valves. In the age of information, valve manufacturers should also go abroad, communicate more with the outside world and users, including engineering design departments. Understand the needs of the customer and working conditions of the valve's medium. Only in this way can we produce suitable valves and build the market. Communicate with foreign valve manufacturers to learn about advanced technologies and new products, and use them to improve our products.
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