A question regarding Class A welds
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Paragraph a) of clause 10.1.6 of GB150 stipulates that all butt welds in various types of convex end closures are classified as Class A welds. What class should butt welds in flat end closures (such as the pressure-bearing ring plates in pressure vessels) be classified as? What is the basis?
The joint seam certainly belongs to Category A welding joints; this is because the flat cover is also a type of end cap. However, the flat cover is subject to greater stress, and it is generally thicker. Heat treatment is required after joining such components. We prefer to use whole plates whenever possible; otherwise, forgings are used instead.
It should belong to Category A joints, mainly analyzed based on the stress conditions of the flat cover plate.
Please note that a flat cover also belongs to the type of end cap, but it is not a convex end cap.
From a stress perspective, there is a significant difference in the stress conditions experienced by flat covers, including ring plates, compared to those of Class A welds as specified in GB150; for example, bending stress generally cannot be ignored.
Based on force analysis, it should belong to Category A, but I have never seen a spliced flat cover
There are many spliced annular flat end caps (plates) in the jacket
Yes, without a doubt it belongs to Category A connectors.
For flat lids, this is a type of end cap； Furthermore, for the flat cover, the theoretical basis used is derived from the mechanical model of a circular plate subjected to a uniformly distributed load with its edges fixed (either by hinges or direct fixation). Since it is difficult in practice to achieve a situation where the edges are fixed, and considering the welded structure between the flat cover and the cylinder, as well as the requirement for good sealing which does not allow for large deformations, the calculation coefficient for the flat cover is based on semi-empirical data; hence, its welded joints belong to Category A welded joints
The welds used for joining in flat end caps are also considered cap joints, and they belong to category A joints
When under compression, flat-end heads are primarily subjected to bending stresses. The welds used to join these flat ends reduce their capacity to bear pressure; therefore, such welds should be classified as Class A welds
Spliced ring-shaped flat end caps (plates) are used in applications with very low pressures; they are typically employed in vessels at atmospheric pressure. Such welds generally fall outside the scope of GB150
They are also useful in pressure vessels; for example, they are commonly used in low-pressure jackets