Διαδικασία κατασκευής δοχείων πίεσης και έρευνα για τον ποιοτικό έλεγχό της
Pressure vessel equipment in many industries in China have a wide range of applications, because the pressure vessel needs to be in a long time in the high temperature and high pressure of the harsh working environment, and the internal holding materials have certain specificity, if you can not guarantee the quality of the pressure vessel, resulting in corrosion of the metal, weld cracking and other quality problems, it is easy to lead to the emergence of the consequences of the serious safety accidents. Based on this, this paper from the actual situation, first of all, explains the pressure vessel manufacturing process, a clear understanding of the pressure vessel manufacturing process problems encountered, and targeting the pressure vessel manufacturing quality control effective means, hoping to provide reference and help for the pressure vessel manufacturing quality control work.
Pressure vessels in the chemical industry, the application of high popularity, the working environment has a greater complexity, if you can not guarantee the quality of the pressure vessel manufacturing, resulting in subsequent quality problems of the pressure vessel, will inevitably lead to a series of safety hazards, a serious threat to the property safety of the relevant enterprises and the personal safety of the staff. In this case, the pressure vessel manufacturing process and its quality control research, for the protection of industry safety, to promote the efficient development of the production and operation of the relevant enterprises are of great practical significance.
1. Pressure vessel manufacturing process
1.1 Safety requirements
Pressure vessels are located in a relatively harsh environment, the need for long-term operation at high temperatures and high pressures, and generally will be held inside the pressure vessel flammable and explosive nature of the hazardous materials, very easy to erosion. The environment and the internal holding material are strongly dangerous, so the corrosion resistance of the pressure vessel, impact resistance have more stringent requirements. Therefore, in the processing and manufacturing process must be in accordance with the requirements of the relevant system for processing and manufacturing, this requirement also has a certain degree of mandatory, must be combined with the relevant standards to strengthen the production quality.
1.2 Pressure vessel raw material selection
One of the most critical aspects of the pressure vessel manufacturing process is the selection of raw materials for manufacturing, the quality of raw materials to a large extent with the quality of the pressure vessel there is a direct link. In this case, it is necessary to comprehensively analyze and clarify the composition and chemical properties of raw materials to ensure that the chemical properties and quality of materials can meet the production requirements. If the quality of raw materials can not meet the standard requirements, then strictly prohibit such materials into production, and combined with the type of raw materials to take the best manufacturing process. At present, the international scope of the pressure vessel production mainly take MnMo-Ni type low alloy high-strength steel as a raw material for manufacturing, the impact toughness of such materials is higher, to meet the demand for pressure vessel manufacturing quality.
1.3 Parts processing and manufacturing
Pressure vessel parts in addition to the head parts, basically will choose forging welding structure as the main means of manufacturing. Pressure vessel large forgings manufacturing for the high temperature requirements, the need for forging raw materials into the furnace forging and continuous heating, if there is a difference in temperature is likely to lead to material destruction. Therefore, in the forging process, the need to start from the characteristics of the pressure vessel parts, combined with the production process for the molding process. Material in the thermal processing process can be utilized normalizing and tempering to avoid cracking problems, thus guaranteeing the good mechanical properties of the parts as well as the integrity of the rough machining of forgings. Pressure vessel cylinder will usually use sheet metal welding structure for the external structure welding, can to a certain extent to ensure the quality of parts.
1.4 Pressure vessel assembly
Pressure vessel parts manufactured after the completion of the need to carry out the assembly of components. Pressure vessel assembly process usually needs to be completed in the production workshop, and at the same time combined with the process content, a small amount of parts of the residual heat treatment, so as to ensure that the parts of the assembly process is carried out efficiently. First of all, in the pressure vessel parts of the inner exterior, nickel-based alloys and stainless steel and other cuts on the cylinder bottom head and other parts of the docking. When the docking is completed to take heat treatment measures to reduce the raw material stress, when the stress removal process is completed and then the pressure vessel components structure for docking, followed by the use of corrosion-resistant sealing surface of the pressure vessel for finishing. If the influence of external environmental factors is large, you can utilize the sub-regional assembly method, sub-type assembly in the manufacturing workshop and on-site, to avoid the problem of poor flange sealing to the greatest extent possible . In order to avoid the deformation problem during the on-site assembly of the pressure vessel, it is necessary to strictly control the welding seam deviation of the pressure vessel, and wait until the assembly of the various components of the pressure vessel is completed in order to check and ensure the quality of the assembly.
2. Problems encountered in the manufacturing process of pressure vessels
2.1 Control problems in the process
Pressure vessels are located in the working environment is extremely harsh, the use of the requirements are extremely demanding, so it is necessary to ensure that the pressure vessel production process to promote the rigorous, scientific, in line with the provisions of the raw materials to give priority to the selection of raw materials to achieve the process of promoting the problem. Because of the rigor of the process, if the intermediate part of the irregularities or errors, it is very likely that it will lead to the subsequent process is difficult to promote, and even pressure vessel manufacturing accidents. In addition, many operators do not have the concept of quality and production accountability concept, resulting in the production of pressure vessels in the process of not following the requirements of the production process, in the selection of raw materials is also less serious, this negligent attitude will make the product quality problems and defects. Relevant enterprises also lack a certain supervision mechanism, personnel responsibilities are divided into fuzzy, non-standardized, unscientific production operations occur from time to time.
2.2 Deformation of pressure vessel
The deformation of pressure vessels is the main problem during the manufacturing period, which is mainly due to the incomplete structural design of the pressure vessel itself, or the difference between the forging of the pressure vessel components and the graphic standards, and the failure to produce in strict accordance with the process and national standards. Among them, a deformation problem arises mainly because of the pressure vessel internal processing of each part of the stress caused by the conflict of stability changes, or pressure vessel internal parts of the welded part of the high temperature state of thermal deformation; another is because of the production process is not rigorous resulting in the manufacture of the period of deviation, including raw material bias, assembly errors, and so on. According to the type of deformation pressure vessel deformation problem also exists in certain remedial differences, part of the deformation is irreversible, difficult to save the material waste . For example, the forging of steel, because the steel itself has high temperature resistance, high deformation difficulty, hardness and other characteristics, but also the main raw material for pressure vessel manufacturing, if the deformation problem or damage during the transportation of the material, will inevitably lead to subsequent parts manufacturing problems.
2.3 Welding heat treatment problems
Pressure vessel manufacturing quality in addition to raw materials and production process, and welding quality is also directly related to the high and low. Therefore, in the pressure vessel manufacturing process must ensure that the welding and subsequent heat treatment work, welding is the main part of the pressure vessel joints and the main structure of the part, the two parts of the welding has a common purpose, is to remove residual stress to ensure that the pressure vessel welded part of the overall organizational properties. However, in practice, it is not difficult to find that many pressure vessel manufacturing process will be selected from different raw materials, welding standards and density of different materials also vary, resulting in more significant heat treatment problems after welding.
3. Effective Means of Quality Control for Pressure Vessel Manufacturing
3.1 Quality control of raw materials
In order to strengthen the manufacturing quality of pressure vessels, it is necessary to standardize the quality of raw materials, so as to lay the foundation for the subsequent quality control of pressure vessel manufacturing. Raw material selection, procurement, acceptance, audit, storage, issuance and other links need to be combined with standardized procedures for strict operation, so as to ensure the quality of materials. Pressure vessels need to be in a relatively harsh working environment for a long time, and the holding material has a special nature, for the physical and chemical properties of the raw material requirements are more demanding. Therefore, the quality control of raw materials for pressure vessel manufacturing should start from the raw material production stage, until the material factory, transportation, to achieve the whole process of tracking the quality of raw materials. In addition, in the pressure vessel manufacturing process needs to be made for the production process and the relevant requirements of scientific selection of raw materials. The relevant manufacturing personnel must be before the formal production of the use of quality control work to carry out strict material control, from the type of material, material, quantity and other aspects of the strict implementation of the material access mechanism. Entering the manufacturing site of raw materials need to be registered by number and archived in the warehouse, for future staff to provide a convenient control of material information. At the same time, also need to pay attention to the corrosion prevention treatment of material storage, to ensure that the service life of the material to strengthen.
3.2 Welding heat treatment quality control
In order to ensure the stability of the pressure vessel manufacturing, to avoid the deformation problem, it is necessary to strengthen the implementation of all aspects of the pressure vessel manufacturing standards, the use of system requirements to regulate production activities, to ensure that the construction personnel can strictly comply with the operating standards to minimize the deformation of the pressure vessel manufacturing problems. Therefore, the pressure vessel manufacturing needs to comply with the national manufacturing standards issued by the State, the unification of different aspects of quality control standards, the use of different aspects of quality control to improve the quality of pressure vessel manufacturing. In this link, we need to pay special attention to the symmetry of the pressure vessel cutting operation, and to ensure that the cutting process of flat orthopedic treatment. The production operation of each link must be utilized to weld heat input efficient docking, in accordance with the process specification standards as soon as possible to start stress heat treatment, as a basis for strict control of welding heat treatment process deformation problems.
In addition, the pressure vessel manufacturing process to a large extent will be affected by the raw materials and production process, if the quality of the material does not pass, the process is not standardized, to a large extent, it will make the pressure vessel deformation problems or even complete damage. In the meantime, in order to avoid such problems it is necessary to apply heat treatment technology for tempering heat treatment or solidification heat treatment, and strictly control the temperature in the furnace to ensure that the furnace heat balance. Especially in the heat treatment before the need to develop a scientific heat treatment process, to ensure that the accuracy of the heat treatment process control, for the avoidance of pressure vessel deformation and other quality problems have significant results.
3.3 Manufacturing process quality control
Pressure vessel manufacturing and processing has certain differences and specificity, pressure vessel manufacturing and processing for the “many varieties, a single set”, in order to realize the scientific guidance for the manufacture of pressure vessels, generally need to combine the above processing principles for the preparation of specialized pressure vessel technology. Determine the manufacturing process will need to ensure that the production process on the strict implementation of process requirements and standardized operation, when the different processes one by one after the end of the relevant quality inspectors and operators need to sign to confirm the completion of the determination of the next sequential determination of the production process.
In this process need to pay attention to the following issues: pressure vessel riveting process first need to clean up the weld holes and set up the relevant installation of the cylinder section; pressure vessel angle weld seam and gasket plate between the uninterrupted welding process; in the pressure vessel pressure test process must have sufficient safety awareness of the responsibility, if there is a leakage problem needs to be first unpressurized for the welding of the supplementary operation, according to the process requirements to determine the value of the test pressure.
The cylinder of the pressure vessel need to strictly control the welded joints on the wrong side of the variable, to ensure the normal molding of the cylinder. For example, the thickness of 16mm steel plate for welding, A class weld joints need to be within 3mm; B class standards have changed, need to be within 4mm. Secondly, the welding axial prong angle during the cylinder reel operation is an important part of it, and it is necessary to control the specification of the reserved indenter of the reel. In order to safeguard the standardization of the prong angle of the barrel section, the relevant angle can be adjusted using the secondary calibration round. The grouping process of the cylinder needs to start from the drawing requirements, especially the upright container, and the straightness of the cylinder should be controlled within plus or minus 15mm.
3.4 Quality control of non-destructive testing
Pressure vessel nondestructive testing is an important quality inspection method after the completion of the production process, and its function can realize a comprehensive inspection of the welding surface quality of the pressure vessel. Pressure vessel nondestructive testing specific methods mainly include ultrasonic, X-ray, magnetic particle, etc., pressure vessel nondestructive testing in an orderly manner, it is necessary to quality control as the implementation of standardized norms, so as to implement the data base in the subsequent testing work, comprehensive penetration of quality control requirements. Relevant inspectors need to start from the inspection standards, strict implementation of technical requirements and system content, to ensure the comprehensiveness and objectivity of the inspection data, the full implementation of quality control requirements. Pressure vessel nondestructive testing is completed, it must be archived to ensure that the archive storage time limit and the normal life of the pressure vessel is proportional.
In addition, according to China’s relevant pressure vessel nondestructive testing requirements, pressure vessel nondestructive testing needs to be detected by ultrasonic or X-ray, in order to ensure the authenticity and objectivity of the test results, it is necessary to start from the design of the drawings to meet the drawing standards. The main elements of nondestructive testing of pressure vessels include the following parts: first, follow the relevant standards and norms, and make the results of nondestructive testing of pressure vessels to match the content of the drawings. Secondly, the wireless detection ratio needs to be combined with the characteristics of the pressure vessel for targeted settings. Third, if the TOFD ultrasonic testing technology is selected, both sides need to be tested beforehand to make an agreement, from both the horizontal and vertical inspection. In the detection process, the ultrasonic waves can be tilted by the steel pipe inside the longitudinal invasion. Transverse detection needs to realize the full position coverage of the weld and ultrasonic intersection position. Fourth, the nondestructive testing process must ensure that the professional competence of the operator can meet the requirements of the operator’s testing qualifications after the audit, the implementation of the review mechanism and the implementation of the judging requirements, to ensure that the wireless testing records and reports are perfect. After the completion of the wireless test report review process needs to be filed in a timely manner. The report of the document can be attributed to the pressure vessel quality document category, so as to realize the effective attribution of the report.
In summary, the pressure vessel is one of the important equipment in the field of petrochemical industry, need to be in a harsh working environment for a long time, for the pressure vessel sealing and corrosion resistance and other performance requirements are extremely harsh, if you can not guarantee the quality of the pressure vessel, it is very easy to have accidents. Therefore, in the pressure vessel manufacturing process should be from the raw materials, welding heat treatment, manufacturing process, non-destructive testing of several aspects of strengthening quality control, comprehensively consolidate the quality of the pressure vessel manufacturing foundation, to reduce the subsequent chemical production of the existence of potential safety hazards.
Author: Li Fufu