Materials prone to delayed cracking should undergo non-destructive testing at least 24 hours after welding is completed

After heat treatment, once the temperature drops to room temperature, non-destructive testing can be carried out. That’s how I understand it personally, but it’s better to wait another day before doing the test.

Which materials delay crack propagation? Which materials suffer from reheat cracking?

Current GB SH regulations stipulate that for steel materials showing such tendencies, after welding, a visual inspection of the welds is conducted; if it passes, heat treatment is carried out followed by non-destructive testing.

Delayed cracking and reheat cracking are two distinct material properties that require separate treatment. To be precise, materials that have a tendency to develop delayed cracks (cold cracks) may develop cracks some time after welding, even without any heating. This phenomenon occurs mainly in materials with high hardenability, such as 15CrMo, 1Cr5Mo, and also materials like 12Cr2Mo1R mentioned earlier. Therefore, for such materials, NDT testing should be conducted at least 24 hours after welding. As for materials that have a tendency to develop reheat cracks, cracks will occur if they are reheated to a certain temperature after welding, regardless of how much time has passed since welding; hence, additional NDT testing is necessary after heat treatment to detect any defects. The material mentioned as 150 is 07MnNiVDR; I recall there being also materials such as 12Cr1MoV, and many others listed in various documents and textbooks. I haven’t encountered them myself, so it’s best to approach them with caution, especially those containing V and Nb