Questions regarding the evaluation rules for filler metals in NB/T 47014 \"Welding Procedure Qualification for Pressure Equipment\"

1. Additional filler metal is a metal material that is added during the welding process to fill the weld and become part of the welded joint. The main difference between it and welding electrodes and wires lies in the terminology. In welding terminology, both welding rods and wires can be considered a form of filler metal. The term “additional filler metal” emphasizes the role of these materials during the welding process—that is, they are added between the base metals to help form the weld. Therefore, functionally speaking, additional filler metals, welding wires, and electrodes play the same role during the welding process. 2. To check whether the contents of important alloying elements exceed the evaluated range, it is usually necessary to refer to the standards or specifications for welding materials. This type of testing usually involves chemical composition analysis, such as the use of spectroscopic methods or other chemical analysis techniques to accurately determine the content of alloying elements in the weld metal. Although Part 6 of the NB/T 47014 standard, \"Inspection Requirements and Result Evaluation,\" does not explicitly require chemical composition analysis, in practical applications, if there is a risk that the content of alloying elements may exceed the specified ranges, it may be necessary to refer to other relevant standards or accompanying technical documents for such analysis. Important alloying elements are those that have a significant effect on the properties of weld metal, such as carbon, chromium, nickel, etc. The contents of these elements affect important properties of the weld, such as its mechanical properties and corrosion resistance. The evaluation range generally refers to the range of alloy element contents specified in the standards or technical specifications used for welding procedure qualification; exceeding this range may result in the weld joint’s properties not meeting the design requirements. Therefore, when changes in the welding process may cause the content of important alloying elements in the weld metal to exceed the specified ranges, it is necessary to employ appropriate chemical composition analysis methods, in accordance with specific engineering requirements and relevant standards, to ensure that the properties of the weld metal meet the required standards. .

For example, when conducting a weld qualification test for the Fe-8-1 group, a qualified weld test was carried out for 30408. According to clause 6.1.2.2 of the standard, 31603 belonging to the same group can be considered applicable. However, the chemical compositions of their deposited metals differ; their mechanical properties are similar, but their corrosion resistance may have changed. In such a case, is the weld qualification result still applicable? Is a re-evaluation necessary?

According to the NB/T 47014 standard, if the welding procedure qualification for Group Fe-8-1 is conducted using 30408 material, then although 31603 material also belongs to the same group, due to differences in chemical composition—and particularly potential differences in corrosion resistance—it is necessary to consider whether the original welding procedure qualification remains applicable. If the operating conditions of the welded components require that the welds have certain corrosion resistance, then even for different materials within the same group, it is necessary to conduct a new welding procedure qualification for material 31603 in order to ensure that the welding quality and weld properties meet the design and operational requirements. Different alloy compositions may have a significant impact on the corrosion resistance of welds; therefore, one cannot rely solely on group classifications to determine the suitability of welding processes. .