Should a margin be left on the weld?
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The master said that after butt welding the pipes, the weld seam should be ground, leaving a residual height of about 1 mm. The reason is that the strength of the weld seam is lower than that of the base material, and it’s not guaranteed that the welding will be 100% complete; therefore, a thicker layer is needed to ensure sufficient strength. But the requirements in the books aren’t that strict either; and for the purposes of flaw detection, it’s necessary to avoid any excess height, ensuring that the weld is at the same level as the base material and is smooth, as excess height can generate stress. People are discussing whether a margin should be left What’s the reason? Please explain by referring to the rules and your own experiences. Thank you; replies will be rated
The weld bead height is merely a requirement of the welding process; it serves to insulate the previous weld pass, slow down cooling, and refine the grain structure. Once welding is complete, the weld bead has fulfilled its purpose; at this point it can be said that the weld bead offers no benefits, as many of the welding defects present in it are actually harmful to the weld joint. It should be removed in theory, but due to production costs, domestic standards allow a remaining height to be retained for containers with lower requirements. However, for containers subject to stress corrosion and fatigue, the excess height must be removed.
In fact, it is best for the weld height to be level with the base material. There is a misconception in China’s equipment manufacturing mindset: having a too-thick weld can cause geometric discontinuities and lead to significant stress concentration, which is not desirable. The strength of the welding material is generally higher than that of the base material, so there is no need to worry about strength issues; problems usually occur in the heat-affected zone.
Thank you for the answers from the two people above. May I assume that there should be no excess height, as it would cause stress concentration? However, I have a question: how can the strength of the weld be higher than that of the base material? Anyway, it was added afterwards anyway
For pressure vessels, it is generally required that the mechanical properties of the welded joints be no lower than those of the base material.
Once, our company delivered equipment to the site, and the client’s staff said, “Your welds are flat (with little root height); look at others’ welds…” ”The delivery person had to use many words to hand over the goods. It is correct in theory, but difficult to accept conceptually.
For 4# luckdog, the strength of the welding rod used must be higher than that of the base material; it usually needs to be only slightly higher, as too large a difference will result in waste
In the past, due to the less advanced welding techniques, the weld was considered to be the weakest part of a welded joint; therefore, reinforcement using a ridge, or what is known as a reinforcement ridge, was employed. With the advancement of welding technology, the strength and other mechanical properties of the weld zone have become superior to those of the base material, making the presence of such a reinforcement ridge unnecessary. From the perspective of strength under static loads, the weld bead height can increase the effective cross-sectional area of the joint, thereby providing reinforcement ； With the advancement of technology, from the perspective of stress analysis, the weld bead height often fails to provide reinforcement; rather, its presence leads to stress concentration.
The analyses provided by the experts are very reasonable. Our company has a similar situation as well; the relevant technical staff, upon seeing the containers that have arrived, say, \"Look at how you welded them.\" The weld is flat.....
http://bbs.hcbbs.com/thread-298473-1-1.html Provides a fairly comprehensive overview
The weld bead should be ground flat as much as possible after welding, in order to avoid stress concentration!