The composite layer of the composite panel is not taken into account in strength calculations; timing for RT testing
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Dear teachers, during today’s group discussion, we talked about when RT testing of composite panel joints should be carried out in cases where the composite layer is not considered in the strength calculations My understanding is: RT can be done after welding at the grassroots level. Ensure strength at the base level, using RT testing for verification ； The transition layer and coating ensure corrosion resistance; PT is sufficient ； But a group member mentioned the practice of performing post-weld UT on the base layer, followed by RT on the entire structure after the cladding welding. After checking HG/T20584-2020, it was found that since the cladding does not contribute to the strength calculation, it is acceptable to carry out RT immediately after welding the base layer, and then perform PT on the cladding ； However, the petrochemical standard SH T3527 states that even if the cladding is not taken into account in the strength calculations, after RT testing of the base layer – followed by the welding transition layer and the cladding – a 5% RT sampling inspection is still required for the entire joint after cladding welding. Two questions: 1) Since the cladding layer does not participate in the strength calculation, and RT is performed on the base layer after welding, what is the problem with not performing RT on the cladding layer after welding? Why is a 5% RT sampling inspection added after the double-layer welding for SH T3527? What is the purpose of this? 2) Suggested by group members: The cladding layer is not included in the strength calculations; only UT testing is performed on the base layer after welding, while RT testing is carried out on the entire structure after the cladding layer has been welded. What is the principle behind this approach to non-destructive testing?
1) The cladding layer is not considered in strength calculations; RT testing is performed on the base layer after welding, while no RT testing is carried out on the cladding layer after welding. This is mainly because the cladding layer serves primarily to provide corrosion resistance rather than strength. The purpose of adding a 5% RT inspection after cladding welding for SH T3527 is likely to ensure that no defects affecting corrosion resistance, such as inclusions or lack of fusion, are generated during the welding process. 2) The reason for performing only UT and not RT after welding the base layer, and then conducting RT after welding the entire structure in layers, is likely that UT can accurately detect internal defects in the base layer, while overall RT can detect defects throughout the joint as a whole. This arrangement can ensure both the strength of the welded joint and the quality of the overall structure. However, whether such an approach is applicable still needs to be determined based on specific circumstances and standard requirements. .
First, use UT to check for defects in the base layer; if no defects are found, then weld the cladding layer, followed by RT. Since RT cannot determine the depth of defects, if RT indicates the presence of defects that exceed the limits, re-coating is considered first. Furthermore, a defect-free base layer may develop defects after welding the coating; for example, excessive current can cause the weld bead to be too deep on the base layer, resulting in a condition of incomplete fusion. In short, after performing manual welding on a pressure-welded joint, non-destructive testing cannot be ignored.