Discussion on the issue of weld overlap
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This post was last edited by ltbandml on 2017-3-8 at 14:25. Material: SA-240M 304, SA-182M F304. Welding rod: ER308. Wire diameter: 1.6, 2.4, 3.2. Welding method: GTAW. Is it feasible to have weld overlaps as shown in the attached diagram? If it’s not possible, please explain the reasons and cite relevant literature; if it is possible, please also explain. Drawing note: The bearing plate T1 is a structural component. After the barrel body T is welded to the barrel body flange ； Then, the backing plate is grooved and welded to the inside of the tank body, with the weld overlapping the butt weld on the inner side.
Such an arrangement is certainly unreasonable; as for the detailed regulations, no standard specifies them in such detail. But the welds overlap, causing stress concentration; it is completely unreasonable, a matter of common sense, for the welds at the attachments of this structure to overlap with the main welds.
It’s unreasonable; the welding stress concentration in three parts is very dangerous for pressure vessels. I’ve never encountered such a design when working on ASME-compliant vessels before. If it’s an unimportant structural component, then it doesn’t matter
The bearing plate is considered a structural component (plate T1 on the far right in the diagram); T represents the thickness of the barrel wall plate； The basic welding structure consists of 1–4 layers of butt welding between the barrel body plates and the barrel body flanges, followed by 5–6 layers of fillet welds at the outer edges with the flanges ； The backing plate is grooved and welded to the inner side of the tank body in 7–9 layers.
I recently encountered this welded joint, and I found it really puzzling as well. But I just can’t find a reasonable explanation; it would be better if you had any information that could serve as evidence.
It cannot be welded this way; move T1 downward to avoid the weld seam.
Stress concentration – that’s definitely unreasonable
The two welds can be offset from each other
Design principles for welded structures of chemical processing equipment: Avoid excessive stress concentration and welding deformation； Facilitates non-destructive testing ； It facilitates welding operations and is beneficial for welding protection, etc. This structure is not suitable.
They generally need to be offset from each other; for the cylinder, it seems that the longitudinal welds are required to be at least 10 times the thickness of the cylinder wall
If the interface formed by the 3 parts is considered as a single welding groove, and the welding process involves the stacking of different weld passes, then there should be no problem with welding. However, the welding deformation of T1 plates is relatively large and difficult to correct, and welding defects are also hard to detect; therefore, such a structure should be avoided.