Classification of welding procedure qualification specimens

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Weld seam and welded joint: “Weld seam” and “welded joint” are two distinct concepts. “A \"weld\" refers to the joint formed after welding of metal parts, whereas a \"welded joint\" is a connection created by welding two or more parts together, or an area that has already been welded. When testing the performance of welded joints, it is necessary to consider the mutual influences among different areas such as the weld seam, fusion zone, heat-affected zone, and even the base material. Weld types are divided into five categories: butt welds, fillet welds, plug welds, groove welds, and end welds. The types of weld joints include: butt joint, T-joint, cross joint, lap joint, plug lap joint, groove weld joint, corner joint, end joint, sleeve joint, oblique butt joint, crimp joint, and root lock joint, totaling 12 types. Classification of test pieces: The objects of classification for welding procedure qualification test pieces are welds, rather than welded joints. From a welding perspective, pressure vessels of any structure are composed of various types of weld joints and base metal; all weld joints are connected by welds, which serve as the foundation for forming different types of weld joints. The performance of welded joints is determined by the welding process used for the welds; therefore, the objects for classification in welding procedure qualification tests are the welds rather than the welded joints. Standard NB/T 47014 classifies the types of welding procedure qualification test specimens into butt weld specimens and fillet weld specimens, and specifies their applicable ranges. No provisions are made for the welding procedure qualification of plug welds, groove welds, and end joints. The welding process that has been approved based on the evaluation of butt weld or fillet weld specimens is not applicable to plug welds, groove welds, and end joint welds; however, the same welding process that has been approved for butt weld specimens is also applicable to fillet welds, based on mechanical property criteria. The relational pattern between butt welds, fillet welds, and welded joints is shown in the figure below, which provides examples of such relationships. From the perspective of classifying weld procedure qualification test pieces, it can be seen that: (1) Not all joints connected by butt welds are butt joints ； Not all weld joints are corner joints. Although the forms of welding joints vary, the form of the welds that connect them can be the same. In other words, the same type of weld can be different welding joints. (2) Regardless of the form of the weld joint in the welded parts, as long as they are connected by butt welds, it is sufficient to use butt weld specimens to evaluate the welding process ； Regardless of the form of the weld joint in the welded parts, as long as they are connected by fillet welds, fillet weld test pieces or butt weld test pieces can be used for welding procedure qualification. (3) The welding process deemed qualified for the butt weld test pieces can be used for the butt welds and fillet welds of various weld joints in the welded parts ； The welding process that has been deemed satisfactory for corner weld test pieces can be used for the corner welds of various weld joints in non-compressed weldments, such as the corner welds between the support plates of horizontal vessels and their shells. (4) The shape of the weld is one of the key factors in determining the items for welding procedure qualification. When determining the items for welding procedure qualification, first, on the drawing, identify in sequence what type of weld is used to connect the various welding joints, and break down the welding joints into welds. For any welded joint connected by butt welds, butt weld test pieces are prepared; the welding process deemed satisfactory for these butt weld test pieces can also be applied to fillet welds. When evaluating a welding process for uncompressive fillet welds, only fillet weld test pieces need to be used. For non-compressive fillet welds such as those between the support pad of a horizontal container and the shell, there are two types of butt weld test specimens: plate-type and tube-type. These two types of specimens follow the same principles when it comes to determining the mechanical properties of the welded joints, with no differences between them. Standard NB/T 47014 stipulates that the welding processes deemed satisfactory for evaluating plate butt weld test specimens can also be applied to tube butt welds, and vice versa.