Precautions for welding procedure qualification

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1. Concept of welding procedure qualification: Welding procedure qualification is the preliminary preparation for 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 designated welded components 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, welding test pieces, inspecting these pieces, and determining whether their welded joints meet all the required technical indicators for desired service performance, in accordance with the proposed welding procedure plan. Finally, all welding process factors, welding data, and test results accumulated throughout the process are compiled into conclusive and recommendatory documentation, thereby forming 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 inspection item for quality and technical supervision agencies during project inspections. It serves as a necessary means to ensure that welding procedures are correct and reasonable. It is also crucial for guaranteeing the quality of welded components; all properties of the welds must comply with the product’s technical specifications and relevant standards. Therefore, it is imperative to verify the correctness and rationality of welding procedures through appropriate tests—namely, welding procedure qualification. Furthermore, welding procedure qualification helps to maximize welding production efficiency and minimize production costs while ensuring the quality of welds, thereby achieving optimal economic benefits. 3. The purpose of welding procedure qualification is that it serves as a technical document to 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 education. (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 and **relevant regulations. IV. Scope of application of welding procedure qualification
(1) Welding procedure qualification applies to the welding work involved in the fabrication, installation, and maintenance of steel equipment such as boilers, pipelines, pressure vessels, and load-bearing steel structures. It also applies to welder training and technical assessment of welders. 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 depending on the type of product. If the product is a pressure vessel, the test results of the procedure qualification must comply with the relevant technical standards for pressure vessels. Similarly, if the product is a load-bearing steel structure, the test results must meet the technical requirements applicable to such structures. In essence, the primary criterion for determining whether a welding procedure qualification test is successful is that it meets the product’s technical specifications. V. Characteristics of Welding Procedure Qualification (1) Welding procedure qualification aims to determine the appropriate welding procedures for any given steel under specific conditions, rather than identifying the optimal process parameters. It operates within certain limits that are generally acceptable to most people. (2) Welding procedure qualification addresses the performance issues under specific process conditions, but it cannot resolve overall quality problems such as stress relief, reduction of deformation, and prevention of welding defects. (3) Welding procedure qualification should be based on the weldability of raw materials. Through reliable technical condition tests conducted during welding procedure qualification, production can be guided, thus avoiding the drawback of using actual products as test pieces. (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 pipes 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. VI. Procedures for welding procedure qualification: Preparing and issuing the welding procedure qualification task sheet – Developing a welding procedure qualification plan – Welding and inspecting test pieces – Compiling a welding procedure qualification report – Based on this report, preparing welding work instructions (or welding procedure cards). 1. Preparing and issuing the welding procedure qualification task sheet. The main purpose of the task sheet 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 indicators: Based on regulations and the theoretical fundamentals of steel (weldability), etc., various technical indicators are determined. According to the provisions of the “Procedures for Welding Procedure Qualification” DL/T869, the chemical composition and mechanical properties (such as strength, plasticity, toughness, etc.) of the weld metal shall be equivalent to or not lower than the corresponding specified minimum values of the base material. (II) Determination of the evaluation items: In accordance with the actual operational requirements of the project, and based on the scope of application of the relevant regulations, the relevant items are identified to determine the evaluation items. The determination of the items for welding process evaluation should be considered from the following aspects: 1. Steel materials (1) Classification of steel grades (2) Basic regulations regarding steel grades in the “evaluation” process (3) Classification of dissimilar steels. A dissimilar steel weld joint refers to a joint formed from different types of steel. Such joints can be basically divided into two categories: one category consists of steels with the same metallographic structure but different chemical compositions, such as weld joints between low-carbon steel and low-alloy steel; both of these belong to the pearlitic structure type, and their physical properties differ only slightly due to differences in chemical composition. The other category includes weld joints where both the metallographic structure and chemical composition are different, resulting in significant differences in physical properties, such as weld joints between low-alloy pearlitic steel and high-alloy martensitic steel or austenitic stainless steel. 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, it is necessary to take appropriate technological measures to address these issues. 1) Type A dissimilar steel joints: The welded joint consists of austenitic steel on one side and steel with another microstructure on the other side. The specific types fall into 3 groups: A+M, A+B, A+P, etc. 2) Class 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; the specific types include 2 groups: M+B, M+P, etc. 3) Type B dissimilar steel joints: One side of the welded joint is bainitic steel. On the other side is pearlitic copper. The specific types are: only one set of B+P. 2 Determination of test piece thickness (1) Butt welds are suitable for weld pieces with a thickness of 1) The thickness of the test piece to be evaluated is 1.5≤δ