Regarding the fixed-type nozzle, setting of the UT inspection range for laminar tearing in the shell base metal

Based on your description, there is a risk of layered tearing in the shell base metal of the fixed-type fitting; therefore, UT (ultrasonic testing) is required to detect defects. You mentioned that the drawing specifies a UT inspection range of 2DOP around the opening, but you believe such a setting may not be very reasonable. First, understand the meaning of 2DOP. 2DOP refers to the opening reinforcement width B=2DOP, where DOP represents the diameter of the opening. Therefore, the 2DOP range is a square area centered on the opening, with a side length of 2DOP. This range takes into account the surrounding area of the opening, which helps to ensure the stability of the opening and the quality of the welding. However, based on your description, the risk of layered tearing in the base material caused by welding shrinkage stress mainly exists in the area of the base material directly beneath the weld, and this risk is essentially absent outside the weld area. Therefore, you believe that it is sufficient to perform UT only on the outermost part of the weld, without the need to conduct UT across the entire 2DOP area. In practical engineering, in situations where high safety requirements apply, conservative approaches are often adopted to ensure safety. Therefore, it is necessary to comply with relevant regulatory requirements and conduct assessments based on specific circumstances. If you insist that performing UT only on the outermost layer of the weld is sufficient, you can communicate with the relevant technical personnel or regulatory authorities, explain your reasons, and seek their advice. Please note that the above responses represent only personal opinions; the specific range for UT should be determined based on actual conditions, regulatory requirements, and professional technical guidance. .

When calculating opening reinforcement, the weld joint coefficient for the 2dop opening reinforcement area is taken as 1.0. Considering the axial force on the mounted nozzle opening, it may cause tearing of the cylinder material within the 2dop reinforcement area of the opening. Ultrasonic testing should be performed on the cylinder plates in this area before marking the openings.

Some of the drawings I’ve come across do indeed include the requirement you mentioned of a UT2 times larger opening diameter; this is often seen in the joints located at the center of manhole covers. As for what range is reasonable, I believe that since this area is already taken into account in the calculations for reinforcing the openings, the base material in this area can theoretically be considered as bearing some of the stress. Since it bears more stress than areas without openings, it should indeed be included in those calculations. Secondly, since the manufacturers of the steel plates used as raw materials have already performed full-area UT, this UT should be carried out after the holes are made.

This post was last edited by wanlirn on 2023-7-12 09:32. Your reference to the standards is also incorrect; GB150.3--D states that fixed-type nozzles should be used, so there will be no delamination in the cross-section of the steel pipe at the opening in the shell. . . . In plain terms, for a fixed-type joint, the weld is applied to the outer surface of the shell; it’s necessary that the entire cross-section be involved in this process, and there must be no delamination. Based on the range of secondary stresses caused by the opening, which is what we refer to as the area that needs reinforcement due to the opening, designers require a distance of 2 times the diameter of the opening – and UT testing ensures that there are no defects. .

In reality, we conduct UT testing based on the hole layout diagram before shell manufacturing; otherwise, all those processing steps would be in vain

This post was last edited by megaherz_IGGE on 2023-7-12 21:06. But adding UT shouldn’t be due to secondary stress, right? If UT is used to increase the layered tearing in the base material due to secondary stresses, then embedded and inserted components should also require UT, after all, secondary stresses are generated by the discontinuities in the openings themselves, not by welding ； Currently, UT is required only for the fixed configuration; it should be based on the fact that the weld shrinkage stress in this configuration is exactly perpendicular to the delamination defects in the shell base material, thereby causing tearing, rather than based on secondary stresses, right? If it’s not based on secondary stress, then logically the UT range shouldn’t be related to the secondary stress range of 2DOP, right? UT should take into account the range of influence of the residual welding stresses at the installation site, right?

You have a misunderstanding; the embedded part is a single forged piece, so there is no such thing as layers. For the plug-type type, full penetration is achieved; delamination occurs because they are welded together and subjected to stress together. Think about it: the fixed welds are located on the outer surface of the shell. What will happen when bending stresses occur or when torque is applied to the connections? Imagine that.

I somewhat understand now. Even if we ignore the effects of welding stress, the stress concentration resulting from the openings themselves, or the bending moments at the joints, can cause effects similar to those of layered defects in the vertical parent material – an effect of tearing away material, similar to how a claw hammer is used to pull out nails while also tearing off a layer of wood from its surface. Is that what you mean?