I have a question regarding the non-destructive testing of CD-type welds

Please carefully review the fixed capacity regulations and GB150; depending on the operating conditions and materials used, surface inspection is required for CD-type welds.

Yes, for CD-class welds, apart from the lugs, the skirt and shell, as well as the surface inspections specified in GB150, basically no surface inspections are required for the rest.

CD-class welds are generally fillet welds; radiography and ultrasonic testing cannot be used due to technical limitations, or the results obtained are not satisfactory. Additionally, depending on the level of importance, magnetic particle testing or penetrant testing can be employed for C and D-class welds, or even both methods may be used

Class C welds are fillet welds; RT or UT cannot be used on them, and generally only MT or PT is employed. For Class D welds, fully penetrated fittings with a diameter of over 200 mm can be subjected to UT testing; in some cases, RT testing is also possible, depending on the testing equipment available at the manufacturing facility and the skills of the testing personnel. Not performing non-destructive testing may be because it is not possible to do so, or it may not be important.

For Class C seams larger than 250 here, surface inspection is usually carried out; it depends on the requirements

The hazards associated with problems in CD-class dry seams are far less severe than those in A-class and B-class welds

Currently, ultrasound and X-rays are not as effective for detecting C and D welds! 2 is that its risk level is lower. Surface inspection is carried out for important items.

In the stress calculation process for CD-type welds, a force analysis shows that the stress at these locations is much lower than that in AB-type welds, resulting in an increased safety factor. The modes of failure and the degree of harm associated with CD-type welds are less severe than those of AB-type welds, and such failures occur on a delayed basis. Due to the structure of the welds, the strength of fillet welds in CD-type welds is higher than that of AB-type welds

At present, radiographic testing can be applied to fillet welds, but due to technical limitations, many companies achieve poor results with this method; however, some highly skilled testing companies manage to obtain quite good outcomes! In fact, photographic testing of fillet welds was developed in Germany during the 1980s and 1990s. Taking the testing of welds between heat exchanger tube sheets and tubes as an example, the use of radiographic testing reduced the probability of leaks at the tube ends in heat exchangers from 18% to 3%. But since this German company kept the technology secret at first, until around 2008; it was only when it wanted to enter the Chinese market that it announced this technology. China was the second country to use ray-based diagonal weld inspection, and the second company in the world to possess this technology was also located in China.