Weld coefficient and non-destructive testing
Thread Content
1. It is stated in UW12 that the joint coefficient depends only on the type of joint and the level of non-destructive testing; then how is the non-destructive testing procedure determined, and what is the basis for this? 2. Can’t the above statement be reversed? That is, the joint coefficient cannot determine the level of non-destructive testing – for example, just because the joint coefficient for Class A welds is 1, it doesn’t mean that Class A welds require 100% testing? 3. For welds of categories A, B, C, and D that do not meet the conditions for UW11 and therefore do not require RT testing, what type of testing should be carried out and what level of testing is necessary? (For example, 100% RT is required for categories A and B, while RT is not needed for categories C and D; so what kind of testing should be done for categories C and D, and what level of testing is required?)
For steel butt welds and fully penetrated butt welds equivalent to double-sided welding: all non-destructive testing φ=1.0； Local non-destructive testing φ=0.85. For single-sided welded butt joints (with gussets in close contact with the base metal along the entire length of the weld root): full non-destructive testing, φ=0.9 ； Local non-destructive testing φ=0.8.
According to UG-116(e) in ASME VIII-1 (2007), there are four notation methods: RT-1, RT-2, RT-3, and RT-4. Among them, RT-1 refers to all RT tests; RT-2 denotes RT testing conducted in accordance with UW11(a)(5) and sampling requirements specified in UW-11(a)(5)(6); RT-3 is sampling RT; whereas RT-4 means that only some of the completed containers meet the RT requirements of UW11(a). In accordance with UW-11 (a) (5)D, full RT is required for Class A and Class D welds, while only sampled RT is required for Class B or Class C welds connected to them; in this case, the weld joint factor remains 1. Given that, based on the stress conditions in cylindrical containers, the circumferential force is twice that of the axial force, it is sufficient for designers to use a coefficient of 0.7 for Type B joints in this case (without performing RT testing), let alone 0.85 (with partial non-destructive testing). The strength obtained is more than adequate, and this approach also provides an excellent balance between risk and design efficiency for such containers.
The selection of weld coefficients in ASME is indeed quite confusing; the answer from the third floor is excellent, so the original poster should take a close look at UW-11.