The significance and purpose of weld process qualification for pressure vessels

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Significance: Welding is an important process in the manufacturing, installation, modification, and maintenance of pressure vessels. The quality of welding plays a crucial role in determining the quality of these processes. The welding quality of pressure vessels encompasses various aspects: the appearance of the welds, welding defects, welding deformation and stress, the performance of the welded joints (mechanical properties, bending properties, corrosion resistance, performance at low temperatures, performance at high temperatures, etc.), and the dimensional characteristics of the welded joints. To determine whether a welding process can ensure the quality of welds on products, it is necessary to conduct verification on test pieces prior to welding; this is the concept of welding procedure qualification. Strictly speaking, weld procedure qualification refers to the testing process and evaluation of results carried out to verify the correctness of the weld procedure for the intended welded components. The welding quality of pressure vessel products refers to meeting the service performance requirements of the welded joints. When performing corrosion-resistant surfacing, the chemical composition of the surfacing layer is the basis for ensuring corrosion resistance. 1. Performance of welded joints Welded pressure vessels are composed of base material and welded joints, and the performance of these welded joints fundamentally determines the quality of the pressure vessel. To determine whether a welding process can ensure the performance of the welded joints in pressure vessels, it is necessary to conduct tests on test pieces prior to welding. The performance of these welded joints serves as the basis for verifying the correctness of the chosen welding process. The welding procedure qualification process involves carrying out welding tests and preparing specimens in accordance with the established pre-welding procedure specification (pWPS), as well as inspecting those specimens, in order to determine whether the welded joint possesses the required performance characteristics. Following this qualification process, a \"Welding Procedure Qualification Report (PQR)\\" is prepared to assess the accuracy of the specified pre-welding procedure specification (pWPS). It can be seen that taking the performance of welded joints as the objective for the process evaluation of pressure equipment is the core idea behind formulating welding process evaluation standards. 2. Chemical composition of the surfacing layer: To determine whether the corrosion-resistant surfacing process can ensure that the chemical composition of the surfacing layer meets the specified requirements, verification must be carried out on test pieces prior to welding. The chemical composition of the surfacing layer serves as the basis for verifying the correctness of the proposed welding process. Using whether changes in welding conditions have caused changes in the chemical composition of the surfacing layer as a criterion for judgment, surfacing process qualification rules are established. The surfacing process qualification process involves welding test pieces and preparing specimens in accordance with the predetermined pre-welding procedure (pWPS) and standard requirements, as well as testing these specimens to determine whether the surfacing layer possesses the desired chemical composition. After the welding procedure qualification, a \"Welding Procedure Qualification Report (PQR)\\" shall be prepared to evaluate the correctness of the proposed pre-welding procedure specification (pWPS). It can be seen that regarding the assurance of the chemical composition of the surfacing layer as a goal for the surfacing process evaluation is the core idea behind formulating rules for the evaluation of corrosion-resistant surfacing processes. Regardless of the objectives of the welding procedure qualification, in order to qualify a welding procedure, it is necessary to first prepare a “prepared welding procedure specification (pWPS)”. The correctness of this prepared pWPS is then evaluated using a “welding procedure qualification record (PQR)”. Purpose The purpose of weld procedure qualification is to determine that the welded joints used in construction possess the required properties for the intended application; weld procedure qualification assesses the properties of the welded joints, not the skills of the welders and welder operators. The basic criterion for assessing a welder’s skills is to determine the welder’s ability to produce high-quality weld metal ； The basic criterion for assessing the skills of welder operators is to determine their ability to operate welding equipment. The purpose of evaluating the welding processes for butt welds and fillet welds is to ensure that the mechanical properties and bending strength of the welded joints meet the specified requirements ； The purpose of evaluating the corrosion-resistant surfacing process is to ensure that the chemical composition of the surfacing layer meets the specified requirements ； The purpose of the additional assessment for welding processes is to ensure that the special properties of the welded joint (such as guaranteed penetration and fillet weld thickness) meet the specified requirements. The correctness of the pre-welding procedure specification (pWPS) is verified by welding test pieces and preparing specimens; whether the welding process is correct or not is indicated by whether the properties of the welded joints meet the requirements. If the requirements are met, it proves that the proposed welding procedure is correct. When used for welding products, the performance of the welded joints of those products can also meet the requirements. The performance of welded joints is a fundamental requirement in design; the correct welding process must be established to ensure that the welded joints possess the desired performance characteristics.