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Concept of welding procedure qualification: Welding procedure qualification is a preliminary step in the entire welding process. Welding procedure qualification is a testing process and evaluation of results carried out to verify the correctness of the welding procedures for the proposed weldments and related products. It includes the processes of pre-welding preparation, welding, testing, and evaluation of the results. Welding procedure qualification is also an important process in production practice; this process has prerequisites, objectives, outcomes, and certain limitations. Therefore, the welding procedure qualification involves carrying out pre-welding preparations in accordance with the established welding procedure plan, fabricating welding test pieces and inspection specimens, and determining various technical parameters to assess whether the weld joints of these specimens possess the required performance characteristics. Finally, all the welding procedure factors, welding data, and test results collected throughout this process are compiled into conclusive and advisory documents, resulting in a \"Welding Procedure Qualification Report\". 2. The significance of welding procedure qualification Welding procedure qualification is an important aspect in ensuring the welding quality of boilers, pressure vessels, and pressure pipelines. Welding procedure qualification is an essential component of the technical preparations prior to welding boilers, pressure vessels, and pressure pipelines. It is a mandatory item that quality and technical supervision agencies check during project inspections; it represents the necessary process to ensure that welding procedures are correct and appropriate. It also serves as an important guarantee for ensuring the quality of welded parts, as well as for ensuring that all properties of the welded joints meet the technical specifications of the product and relevant standard requirements. Therefore, it is necessary to verify the correctness and rationality of the welding process through corresponding experiments, namely welding procedure qualification. Welding procedure qualification can also help to improve welding production efficiency and minimize production costs while ensuring the quality of the welded joints, thereby achieving the greatest economic benefits. The purpose of the three welding procedure qualifications is to serve as technical documents that must be followed in the production processes such as manufacturing, installation, and maintenance of boilers, pressure vessels, pressure pipelines, and equipment, as well as in welder training and instruction. 2 are the key steps or important measures to be implemented in welding quality management. 3 is an important indicator reflecting the welding capacity and technical level of a unit. 4 are items that must be carried out as stipulated by industry standards and **relevant regulations. 4 Scope of application for welding procedure qualification 1 Welding procedure qualification is applicable to the welding work involved in the fabrication, installation, and maintenance of steel-based equipment such as boilers, pipelines, pressure vessels, and load-bearing steel structures. It is also used for welder training and the assessment of welder skills; welding procedure qualification must be carried out prior to these activities in order to determine the correctness of the proposed welding procedures. 2 Welding procedure qualification applies to welding methods such as shielded metal arc welding, tungsten inert gas welding, gas metal arc welding, flux-cored wire arc welding, oxyacetylene welding, and submerged arc welding. 3 Enterprises engaged in manufacturing, installation, or maintenance work. 4. Welding procedure qualification is context-specific; the technical requirements vary for different products. If the product is a pressure vessel, then the test results of the procedure qualification must comply with the technical standards applicable to pressure vessels ； If the product is a load-bearing steel structure, the results of its process qualification tests must meet the standard requirements specified for the technical specifications of that load-bearing steel structure. The primary requirement for passing welding process qualification tests is to ensure that the welding process meets the technical specifications of the product. 5 Characteristics of welding procedure qualification 1 Welding procedure qualification is aimed at resolving the welding process issues related to any given steel under specific conditions, rather than selecting the optimal process parameters; it operates within certain limits that are acceptable to most people. 2 Welding procedure qualification addresses issues related to service performance under specific process conditions; however, it cannot resolve overall quality issues such as stress relief, deformation reduction, and prevention of welding defects. 3 Welding procedure qualification should be based on the weldability of the raw materials, and through reliable technical condition tests conducted as part of welding procedure qualification, production can be guided, thereby avoiding the drawback of using actual products as test specimens. 4 Human factors should be eliminated during the welding procedure qualification tests, and welding procedure qualification should not be confused with welder skill assessment. The person in charge of conducting welding procedure qualification should be able to determine whether the cause of defects is a problem with the welding procedure or the welder’s skills; if it is a skill issue, it should be resolved through welder training. 5 The tests required according to the existing welding procedure qualification regulations are mainly mechanical tests of the welded joint at room temperature. That is, upon passing the visual inspection, non-destructive testing, and room-temperature mechanical tests, it is generally considered that the welding procedure test has been passed. For new steel grades for high-temperature and high-pressure pipelines in the power industry, this result is not entirely reliable; tests such as high-temperature endurance tests, creep tests, and stress corrosion tests on the joints also need to be considered. 6. Procedures for welding procedure qualification: Issuing the welding procedure qualification task assignment – Preparing a welding procedure qualification plan – Welding and inspecting test specimens – Compiling a welding procedure qualification report – Based on this report, preparing welding operating instructions (or welding procedure cards). 1. Issuing the welding procedure qualification task assignment: The main purpose of the task assignment is to assign the qualification tasks. Therefore, its key contents should include: the purpose of the qualification, evaluation criteria, specific items to be evaluated, as well as the qualifications required of the departments and personnel responsible for carrying out the qualification. (1) Determination of evaluation criteria: Various technical criteria are established based on regulations and the theoretical fundamentals of steel (weldability), etc. In accordance with the provisions of the \"Code for Welding Procedure Qualification\" DL/T869, it is required that the chemical composition and mechanical properties (such as strength, plasticity, toughness, etc.) of the weld metal shall be comparable to those of the base material, or not lower than the minimum specified values for the base material. (2) The determination of the evaluation items is based on the actual operational requirements of the project; relevant items are covered in accordance with the scope of application of the regulations, thereby identifying the items to be evaluated. The determination of items for welding procedure qualification should be considered from the following aspects: Steel materials (1) Classification of steel material grades ； (2) Basic provisions regarding steel grades in “Evaluation” ； (3) Classification of dissimilar steels: The term “welded joints of dissimilar steels” refers to the fact that the combinations of steels in such joints can be broadly categorized into two types. One type consists of steels with the same metallic structure but different chemical compositions; an example is the welded joint between low-carbon steel and low-alloy steel. Both of these steels have a pearlitic structure, and their physical properties are quite similar; only their chemical compositions differ ； The other category involves cases where both the metallic microstructure and chemical composition are different, resulting in significant differences in physical properties; examples include welded joints between low-alloy pearlitic steels and high-alloy martensitic steels or austenitic stainless steels. The main characteristics of dissimilar steel weld joints are: the resulting weld joints exhibit inhomogeneities in chemical composition, metallographic structure, mechanical properties, and distribution of welding residual stresses. Therefore, during the welding process, necessary technological measures must be taken to address these issues. ①Type A dissimilar steel joints: One side of the welded joint is austenitic steel, while the other side is steel with other microstructures. The specific types include 3 groups: A+M, A+B, A+P, etc. ②Class M dissimilar steel joints: One side of the welded joint is made of martensitic steel, while the other side is made of steel with a different microstructure; there are 2 groups of such types: M+B, M+P, etc. ③Class B dissimilar steel joints: One side of the welded joint is made of bainite steel. On the other side is pearlitic copper. The specific types are: only one group of B+P. 2 Determine the thickness of the test piece: (1) Butt welds are suitable for weld pieces with a thickness of ①; the thickness of the test piece to be determined is 1.5 ≤ δ