A weld bead is applied around the surface of the head at the junction with the skirt
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Recently, the company manufactured an adsorption tower that was designed using analytical methods; its operating pressure ranges from -0.09 to 3.0 MPa, with a design pressure of 3.3 MPa, and it is classified as a Class III vessel. The head material is Q345R (normalized). There is a transition section of 500 mm in length at the junction between the skirt and the head, and its material is the same as that of the head, namely Q345R. However, the drawings specify that a shielding layer with a thickness of 6 mm should first be welded on the surface of the head at this junction. Why is this?
Is it to avoid stress concentration or due to considerations related to welding? We can’t do stress analysis
During the forming of the head here, it forms an arc-shaped area where thinning occurs; SAW cladding is used to increase the wall thickness as well as the weld strength between the head and the skirt.
Personal opinion: It’s equivalent to applying a transition layer, which prevents direct contact between the head and the skirt. Since the operating conditions of the head and the skirt differ greatly, with variations in temperature and pressure, this approach is used to avoid thermal stress or fatigue issues caused by changes in the forces acting on the head.
Personal opinion: 1. There is an angle (dead corner) between the skirt and the head; the surface of the head at this angle is prone to corrosion, and welding a layer around it can effectively enhance the head’s resistance to corrosion. 2. Due to the significant differences in operating conditions between the head and the skirt, with varying temperatures and pressures, fatigue caused by temperature stress needs to be avoided.
1. Anyone who has worked on the analysis of **loaded towers or vertical vessels with skirts knows that the weakest point in the skirt is the weld at the junction between the skirt and the head; increasing the weld thickness by 2 mm significantly reduces the stress. One of the purposes of welding a ring is to increase the cross-section of this weld and reduce stress. 2. This device operates in a vacuum condition; it has a tendency to move inward, and the supporting force is also the surface pressure. The second objective is to increase the compressive strength in this area. As for whether there will be any thermal stress, that depends on the actual operating conditions of the equipment. Generally, there is hardly any. At low temperatures, there is no insulation, so there can be no thermal stress; at slightly higher temperatures, since there is insulation on both the inside and outside, there is also little thermal stress. (Those who have worked with fatigue caused by temperature fluctuations in equipment know that the thermal stress resulting from temperature differences in such equipment is quite low.) When analyzing and modeling this equipment, I think the designer did not include a surfacing layer. If the original poster has analysis reports, it would be worth taking a look at them. Since I haven’t seen the detailed parameters, and many of those parameters cannot be shown on the drawings, that’s all I can think of for now. (Because many people mentioned thermal stress, that’s why this approach was used as well.)
Reply to 6# Hunk, thank you for your answer; I’ve learned something