Seeking help again regarding the non-destructive testing of D-welded joints~
Thread Content
This post was last edited by deus on 2010-8-25 at 11:47. I posted a similar message before, but unfortunately it went unnoticed with no replies; I’m posting it again today. I hope the moderators can understand. GB150 specifies ultrasonic or radiographic testing for Class A and B weld joints, while only surface inspection is required for Class D joints. Under what circumstances are radiographic or ultrasonic tests necessary for Class D welds? Today I came into contact with a set of equipment designed for use with hydrogen and wet H2S; the design pressure is 7 Mpa and the design temperature is 280°C. One of the technical requirements states that \"Welded joints of category D with an inner diameter greater than 200 mm must undergo 100% ultrasonic testing in accordance with JB/T4730-2005, and they must meet grade I standards.\" What is the basis and source for this requirement? Looking forward to your advice. Thank you!
I also often see that technical specifications for drawings require ultrasonic testing for large joints larger than 200 in size; for small joint fillet welds, surface testing is generally done because ultrasonic testing is difficult to carry out on such small components. For joints larger than 200, 100% ultrasonic testing is required, and the acceptance standard follows that of the cylinder itself. There seems to be no standard mandatory regulations; it’s the additional technical requirements established by convention in the design institutes. I seek advice from those who are more knowledgeable
They are just general design requirements; we have also encountered cases with 100% RT, regarding the welds between the large nozzles and the cylinder body
There is no solid basis for this; it’s meant to improve the safe use of equipment and reduce the risks for design firms
We have also encountered such situations, usually with nozzles and cylinders of DN200 or larger, using media that are flammable, explosive, or highly toxic. 100% UT is required for the takeover and Class D welds of the cylinder as specified in the drawings.
Reply to 2# realben: Personal opinion: 1. Importance: The joints connecting the take over to the casing are subject to high constraints, resulting in significant stress concentration; moreover, the weld metal usually has lower plasticity than the base material, and cracks generally originate from these areas. In conventional design calculations such as GB150 (primary film stress), the effect of stress concentration is not taken into account; instead, it is controlled through special manufacturing requirements. 2. The conventional approach without any specific requirements: During welding operations, gas cutting and gas gouging are commonly used to create the saddle-shaped openings manually; it is difficult to ensure the correct angle of the groove and the proper size of the root edge. The oxide scale on the surface of the groove cannot be removed effectively, and the working conditions are not conducive to achieving the desired shape. Therefore, defects such as cracks, lack of penetration, lack of fusion, and slag inclusions are very likely to occur. With no requirement for non-destructive testing, welders’ sense of responsibility also decreases. Quality is hard to guarantee. 3. Put forward requirements: These are generally specified only in special operating conditions (fatigue, low temperatures, large temperature gradients, toxic or hazardous media, and sometimes flammability and explosivity). It is best to use a saddle-type cutting machine to create the groove; even in the absence of such a machine, the quality of the groove must still be ensured. A fully penetrative welding process should be employed, either through double-sided welding with backside cleaning for root removal, or through single-sided welding with TIG welding for the root portion. Therefore, it is reasonable and necessary to propose non-destructive testing for the special operating conditions of Class D connectors.