On the non-destructive testing of small-diameter fittings
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It has been a long time since GB150-2011 was issued. Recently, I was involved in a project where there were four design firms responsible for the container design. One issue was identified: the drawings prepared by these three firms did not specify any separate requirements for non-destructive testing of fittings with a nominal diameter of less than 250. However, according to GB150, specific requirements shall be specified by the designer. There is no other option; the response from the design firm was that non-destructive testing requirements for welds of types A and B should be applied uniformly. It’s frustrating – such strict requirements are too much for the small connections on ordinary containers.
As explained above for 150 and Ronggui, they are mainly divided into two categories: 1. Welded joints of types A and B are subject to either radiographic or ultrasonic testing (10.3.1); the butt joints of the nozzles are inspected in accordance with the requirements specified in 10.4(h), along with surface non-destructive testing. 2. Welded joints of types A and B are subjected to partial radiographic testing (10.3.2), in line with the provisions outlined in the design documents；
But the design agency said to follow the requirements for Class A/B welds, which means radiographic testing is necessary.
“10.3.3 The inspection requirements for pipe fittings with a nominal diameter DN < 250 mm, as well as for joints where pipe fittings are connected to flanges, shall be in accordance with the provisions specified in the design documents. ”It refers to the requirement that radiographic or ultrasonic testing be carried out in accordance with the provisions of the design documents; no mandatory standards exist for this. “10.4 Surface inspection: Welded joints that meet one of the following conditions shall have their surfaces inspected by magnetic particle or penetrant testing, in accordance with the methods specified in the drawings: h) Joints where tube connections have a nominal diameter DN < 250 mm, as well as joints between tube connections and high-radius flanges, on containers for which full radiographic or ultrasonic testing is required ； ”It refers to the surface inspection requirements; for containers with a nominal diameter DN < 250 mm, where all joints such as pipe-to-pipe connections and pipe-to-high-radius flange connections are to be inspected by radiographic or ultrasonic testing, magnetic particle or penetrant testing must be specified in the design drawings ； For fittings with a nominal diameter DN < 250 mm on containers that require local radiographic or ultrasonic testing, it is up to the designer to decide whether magnetic particle or penetrant testing shall be carried out on the fittings’ butt joints and connections with high-radius flanges; there are no mandatory requirements in the standards. When communicating problems with the design institute, it is necessary to explain the problem, its causes, suggestions for solutions, and the basis for those solutions. Otherwise, the design institute will simply say, \"Construct according to the drawings,\" or give requirements that are difficult to meet – which is nothing but causing trouble for oneself.
Thank you very much. The issue lies in a lack of communication with the design team. But should the requirements for non-destructive testing of the small connections be specified in the design drawings? These requirements are indeed stipulated in the standards, yet they are not reflected in the design drawings.
Yes, there are many things that need to be done. We also often neglect, disclose, or even make mistakes. The design institute is the same; sometimes it is unable to face up to its own mistakes. Therefore, it is necessary to clearly state the reasons, suggestions for solutions, and the basis for those solutions, and finally add: Is it appropriate to handle this in this way? Please reply. Design institutes are more willing to accept it.