[Discussion Thread 27] In what aspects are the surface quality and aesthetics of pressure vessels primarily reflected?

The surface of the material must be free of pits and weld beads; the welds should be smooth without undercuts, and the excess height must meet the standard requirements. The rust removal and coating processes must comply with the relevant standard specifications.

There is also room for further discussion: such as painting, polishing, matte finish, brushed finish, mirror finish, hot-dip coating, colored zinc plating, and so on

Although the visual quality of a product may not affect its operational safety, it does have a direct impact on its quality level and market competitiveness. The following factors affect the visual quality of the product: 1. The quality of weld formation, including: the width of butt welds, control of weld excess height, and the appearance of fillet welds. 2. Are there any splashes, arc pits, oxide scale, etc. on the surface of the container plate? 3. The roughness of the cutting surfaces of supports, lifting lugs, etc., whether chamfering has been applied, and the presence of burrs, etc. 4. Assembly quality: misalignment of the joint surfaces, edge angles, etc ； Are the vertical and horizontal deviations of the pipe outlet installation in compliance with the regulations? 5. Check whether the weld layout is reasonable and aesthetically pleasing; openings should be avoided as much as possible near welds. 6. Check whether the surface of the stainless steel products is well protected, free from scratches and contamination, and whether there are any persistent dark spots left after pickling and passivation. 7. Quality of the surface paint: whether the paint film thickness is uniform, whether the color is consistent, and whether there is any paint accumulation.

This post was last edited by kareale88 on 2019-3-20 at 10:03. Discussion on Several Issues in Pressure Vessel Manufacturing by Liu Shoujun. When pressure vessel manufacturing companies implement regulations and standards such as the \"Regulations on Safety Supervision of Pressure Vessels\" (hereinafter referred to as the \"Vessel Regulations\"), GB150-1998 \"Steel Pressure Vessels\", and GB151-1999 \"Shell and Tube Heat Exchangers\", discrepancies in the interpretation of certain provisions in these regulations and standards lead to many disputes in actual operations, forcing manufacturing companies to take many detours. The following prominent issues will be discussed here; we hope that colleagues in the industry will share their opinions widely. (1) Is it necessary to prepare a product welding test plate for butt-welded hot-pressed heads? Some manufacturing units believe that although a product welding test plate is prepared for the longitudinal seams of the cylinder body (without heat treatment), a separate product welding test plate is required for heads with butt welds that are formed by hot forming using the same steel grade and welding process. This is because the heat treatment requirements for heads differ from those for cylinder bodies. Article 12 on post-weld heat treatment in the standard JB/T4746-2002 \"Heads for Steel Pressure Vessels\" also states that for heads formed by hot forming, when the final pressing temperature reaches or exceeds the specified post-weld heat treatment temperature, the hot forming process is considered to have simultaneously performed the post-weld heat treatment. Accordingly, as stipulated in Article 77 of the Pressure Vessel Regulations, when different heat treatment specifications are applied to the same product and the scope of welding procedure qualification for different longitudinal weld joints on the pressure vessel (including those on heads, tube boxes, and cylinder bodies) varies, separate welding test plates should be prepared for each corresponding longitudinal weld joint using the appropriate welding procedures. This understanding is incorrect; end caps do not require product welding test plates. This is clearly stated in Article 14 of the Answers to Questions (III) in the \"Regulations for the Safety Inspection of Pressure Vessels\" (99th edition), published in the 5th issue of the \"Pressure Vessels\" magazine in 2003. It is worth noting that although welded-seamed hot-pressed heads do not require product welding test plates, when complying with JB4708-2000 \"Welding Procedure Qualification for Copper Pressure Vessels,\" welded-seamed hot-pressed heads still need to undergo welding procedure qualification prior to product welding. If the pressure vessel manufacturer has not conducted a welding procedure qualification for the hot forming of butt-welded heads using post-weld heat treatment at temperatures above the upper transition temperature (such as normalizing), such qualification must be carried out as a supplement. (2) Selection of low-hydrogen and non-low-hydrogen electrodes in pressure vessel manufacturing. In the manufacture of pressure vessels, the selection of welding materials is extremely important; relevant provisions are outlined in JB/T4709-2000 \"Welding Procedures for Steel Pressure Vessels\" (a recommended standard). Can welding rod type E4303 (J422) be used for welding Q235-B after passing the welding procedure qualification? It is a misconception to think that all types of pressure vessels made from Q235-B material can be welded as long as the welding procedure qualification is successful. The J422 electrode corresponds to E4303 in the GB/T5117-1995 standard for carbon steel electrodes; this standard requires that the impact absorption energy of the weld metal at 0°C be ≥27 J. According to the \"Product Catalogue for Welding Materials,\" J422 ensures a value of ≥27 J at 0°C, with typical values of ≥4 J at -20°C. The mechanical properties and bending strength of the welded joints fully meet the requirements of the standard. Although the welding procedure qualification was successful, it is still recommended not to use this qualification for welding Q235-B steel products. Whether a qualified welding procedure can be applied to such products depends on other factors as well. The J422 electrode is a titanium-calcium type, non-low-hydrogen electrode; during welding, it results in a high level of diffused hydrogen in the weld metal, leading to poor crack resistance, which is why it is not suitable for welding pressure-bearing equipment. Therefore, when welding pressure vessels and their main pressure-bearing components, we should select low-hydrogen electrodes based on factors such as the chemical composition, mechanical properties, and weldability of the base material, taking into account the specific characteristics of the pressure vessel, its operating conditions, and the welding method used. Low-hydrogen electrodes shall be used for Class II and Class III pressure vessels that meet the requirements of the \"Regulations on Safety Inspection of Pressure Vessels\". This is covered in HG20581-1998 \"Specifications for the Selection of Materials for Steel Chemical Storage Vessels\". Furthermore, some design and manufacturing units for pressure vessels recommend using the E5016 electrode when welding steel grades such as 16MnR, which I believe is inappropriate. When comparing the process performance of the two welding electrodes, E5015, and E5016, it is evident that E5015 is superior to E5016 – a fact recognized by many welding professionals. In terms of welding power sources, E5015 requires a direct current power source, while E5016 can be welded using an alternating current welder. Given the widespread shortage of direct current welders in China, E5016 was developed based on E5015; however, its arc stability is still inferior to that achieved when using direct current for welding with E5015. Moreover, due to its limited usage, whether E5016 is readily available on the market is a matter that needs consideration. Taking these three points into account, when welding 16MnR steel in pressure vessel manufacturing, E5015 is indeed the better choice. (3) Post-weld heat treatment of tube boxes and product welding test plates: In accordance with the provisions on manufacturing, inspection, and acceptance in Chapter 6 of GB151-1999 \"Shell and Tube Heat Exchangers\", tube boxes made of carbon steel or low-alloy steel and equipped with partition plates must undergo stress-relief heat treatment after welding. However, many manufacturers do not determine the heat treatment holding temperature and holding time accurately; in the specifications for post-weld heat treatment, the holding temperature plays a much more important role than the holding time. A factory used 16MnR to manufacture heat exchangers, and a range of 600°C to 640°C was specified for the heat treatment temperature of the tube boxes. JB/T 4709-2000 \"Welding Code for Steel Pressure Vessels\" (a recommended standard) also adopts this specification. When asked about its meaning, two interpretations were given: ① It is considered satisfactory as long as the temperature is maintained within the range of 600°C to 640°C ； ②Within the range of 600°C to 640°C, a deviation of +20°C is allowed at both 600°C and 640°C. The author believes that in JB/T4709-2000 \"Welding Code for Steel Pressure Vessels\", the exact meaning of the post-weld heat treatment temperature is that a deviation of plus or minus 20°C is permitted at a holding temperature of 620°C. Therefore, when formulating heat treatment processes in the future, pressure vessel manufacturers should set the heat treatment holding temperature at 620°C (620°C ± 20°C), rather than 600°C or 640°C. The shell side of a heat exchanger is generally not subjected to heat treatment, while the tube box, due to the presence of partition plates for dividing the flow, requires heat treatment to relieve stress. Some people believe that the same product may require different post-weld heat treatment procedures; according to the relevant regulations, separate weld test plates must be prepared (except for seamless steel pipes). This understanding is unfounded and unscientific. It is considered unfounded because there are no provisions regarding this in GB151-1999 \"Shell and Tube Heat Exchangers\" or other standards; on the contrary, Article 7(7) of the explanatory notes to GB151-1999 states that \"when reinforcement is achieved by thickening the tube box stub as a whole, and the welding joint factor for Class A stubs is determined based on the corresponding welding procedure qualification, it is not necessary to use a product welding test plate.\" ； It is considered unscientific because the test plate was welded at the extension of the longitudinal weld it represents, eliminating the welding stresses associated with the use of welding partition plates. What is the purpose of using a heat-treated test plate to examine welds under different loading conditions? It can be seen that the purpose of heat treatment for the tube box is to eliminate the stresses resulting from welding the partition plates, and there is no need to use heat treatment test plates for the tube box sections. References: 1. Magazine \"Pressure Vessels\", Issue 5, 2003 – Interpretation of the \"Customer Regulations\" (Version 99), Part 3. 2. Magazine \"Pressure Vessels\", Issue 6, 2004 – Explanation of Welding Procedure Qualification for Steel Pressure Vessels, Part 1. 3. HG20581-1998 – Regulations on the Selection of Materials for Steel Chemical Process Vessels. Interpretation of Standard 4 GB151-1999 \"Shell and Tube Heat Exchangers\", Yunnan Science and Technology Press. Author: Liu Shoujun, Technical Department of Xinli Water Supply Equipment Co., Ltd., Jinan, Shandong Province, Postal Code 250022

Quality Control in Pressure Vessel Manufacturing Quality Control in Pressure Vessel Manufacturing Abstract: Pressure vessels are a type of special equipment, and their quality has a direct impact on the safety of people’s lives and property. Based on the impact of the five key factors in the pressure vessel manufacturing process, this article introduces detailed measures to improve the quality of pressure vessels. Keywords: quality ； Pressure vessel ； Control DOI: 10.19354j.cnki.42-1616/f.2016.17.47 Introduction: Pressure vessels are a type of special equipment that are widely used in industries such as petroleum, pharmaceuticals, chemicals, and metallurgy. If pressure vessels lack safety measures during design, manufacturing, and installation, the consequences of any accidents that may occur could be immeasurable. To use pressure vessels safely, their quality is extremely important. Based on the impact of the five key factors in the pressure vessel manufacturing process, this article introduces detailed measures to improve the quality of pressure vessels. I. Quality analysis of pressure vessels: The quality of pressure vessels is determined by the quality of their design, manufacturing, and installation. Among these determining factors, the quality of manufacturing is extremely crucial. Its design quality plays a decisive role in the manufacturing quality; many manufacturers choose design agencies of low overall standard, which results in the standards adopted during design not meeting the required levels. II. Factors Affecting Quality in the Manufacturing of Pressure Vessels and Control Measures (1) Materials and components. Raw materials and components are a very important aspect of manufacturing; relevant manufacturers must establish strict rules regarding the procurement, inspection, and labeling of such materials and components to ensure the proper production of pressure vessels. Detailed control methods: Purchasers determine the documents to be acquired based on the designed drawings and instructions, and establish relevant records for suppliers that meet the required standards. After preparing the procurement documents through a dynamic review process, the company’s purchasers enter into contracts with suppliers who offer good quality at competitive prices. The procurement contracts must include clear provisions regarding quality assurance, and the inspection methods must also be specified. Once the materials and components arrive at the factory, inspectors must verify them in accordance with established standards and confirm their compliance before allowing them to be stored in inventory. Those substandard materials must be isolated and labeled. The storage keeper of raw materials must classify them into the inspection area, the rejected area, and the approved area based on their specifications, models, and material types, in order to prevent the use of raw materials that do not meet the requirements specified in the drawings. Substitutive procedures for presenting the required documents must be completed before further steps can be taken. (II) Process. To ensure that pressure vessels remain under controlled conditions at every stage of manufacturing and to guarantee that their quality meets the standards and regulatory requirements, strict regulations must be in place for their manufacturing processes and production management. Relevant process documents should be established for pressure vessel products. For those devices manufactured on a large scale, universal procedures need to be established. The latest pressure vessels feature new technologies and processes, so relevant process plans must be developed. Then, strictly implementing the established process plan in production is a very crucial step. (III) Welding. (1) Welders working on pressure vessels must first pass the examination stipulated in the unit’s \"Rules for the Examination and Management of Welders for Boilers, Pressure Vessels, and Pressure Pipelines\", and obtain a qualification certificate for welding special equipment before they can carry out such welding work within a specified period. It is prohibited for unqualified persons to engage in welding work, and welders must carry out welding operations in accordance with the relevant regulations. (2) The materials to be welded must meet the relevant industry and **standards; they must also be stored, inspected, and used in accordance with the relevant specifications and standards. (3) The welding procedure documents are intended to guide the work of welders; first, they must be evaluated in accordance with the technical specifications for pressure vessels, as well as relevant welding regulations and procedures, in order to establish specific welding procedure documents. (4) The environment, processes, and inspections for welding pressure vessels must be carried out in accordance with the guidelines of relevant processes as well as the process cards. (5) Welding equipment must be used and managed by professional welders. The voltmeters and ammeters of the welding equipment must have proper labels in accordance with relevant regulations, and they must remain in good condition throughout their useful life. (6) If excessive defects are detected in the weld during repair, it is necessary to analyze the causes of these defects and develop plans for repair and re-welding. (7) Records of welding. Records of welding operations are also a key factor affecting quality in manufacturing; such records must accurately and objectively reflect the conditions at the work site. (IV) Non-destructive testing. Non-destructive testing is a crucial method for ensuring the quality of pressure vessels. Personnel responsible for non-destructive testing of equipment must undergo training and assessment provided by their respective organizations, and only after obtaining the appropriate professional qualification certificate for special equipment can they carry out such testing. Before non-destructive testing, the inspector must determine the testing plan based on the non-destructive testing procedures and technical drawings. During the testing process, it is necessary to record in real time the parameters of the testing conditions as well as the quality status. After the testing is completed, a qualified inspector must fill out the test report. The results of the non-destructive testing indicate that repair is necessary; the inspector must provide a repair notice and hand it over to the client for carrying out the repairs. (5) Withstand voltage test. The pressure test is a crucial method, carried out after the manufacture of pressure vessels, to ensure the product’s sealing performance, strength, and safe operation. The voltage resistance test must be carried out in accordance with **the relevant regulations**. Before conducting the voltage withstand test, it is necessary to collect and compile the inspection and test records and reports. After passing the review by the quality supervisor, those that meet the standards are sent to a testing agency for further verification. Every part of the pressure vessel under inspection must be securely connected and fully assembled. The testing site must have appropriate safety measures in place, and testing can only proceed after being inspected by the unit’s technical staff and the safety department. Ensure that the strength and safety of the pressure vessel remain unaffected during testing. If issues such as pressure instability are detected in the pressure vessel during testing, it is necessary to release the pressure first, and then conduct testing again after repairs are completed. Conclusion: In recent years, pressure vessels in China have seen significant improvements in both quality and performance, and are now generally capable of meeting the production needs of industrial enterprises. Based on the impact of the five key factors in the manufacturing process of pressure vessels, this article introduces detailed measures to improve the quality of such vessels, with the hope of providing assistance to relevant professionals. References: Zhang Lanqing, Liu Guoyin. Research on Quality Control Methods for Pressure Vessel Manufacturing. Small and Medium Enterprises Management & Technology (Monthly Issue), 2013(07)