Why aren’t expansion joints used in pipes?
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I specialize in equipment design, and expansion joints are commonly used for compensation in such systems. Why then isn’t this practice widely adopted in pipeline design? Instead, large rectangular bends are used, which are costly, labor-intensive, and take up more space? (For ordinary pipelines)
It’s useful too, but it’s particularly troublesome. If a bend pipe can be used, use it first.
The calculation, design, installation, and maintenance of pipe expansion joints are all quite troublesome; using π bends is simpler and more convenient
On the one hand, the cost of expansion joints is slightly higher than that of elbow fittings; on the other hand, expansion joints are prone to leakage, resulting in higher maintenance costs. Therefore, under normal circumstances, it is advisable to use natural compensation for thermal displacement and thermal stress
Hello, indeed expansion joints are more expensive on their own, but carbon steel ones don’t cost much more either. That large bend in the pipeline requires supports, and those supports need a foundation; piloting may be necessary as well. Including the cost of the pipeline material itself and the construction structure, it will definitely be more expensive than an ordinary carbon steel expansion joint. Expansion joints are prone to leakage, but in our company we handle dozens of projects per year, and I’ve never heard of any leakage issues with the expansion joints of those heat exchangers (those without low-pressure outlets). There must be some leaks, but the many welds present in large pipe bends also increase the risk of leakage, requiring additional inspections.
The stress conditions on the expansion joints of piping systems are much more complex than those on heat exchangers, and both system design and manufacturing require technicians to possess a high level of expertise. Furthermore, although there are many large bends in the pipes and thus many welds, the risks are much lower compared to those of the welds at expansion joints. If an accident does occur, at most the pipeline will leak, while the expansion joint, due to its weak structure and poor stability, is very likely to explode, with consequences that are often catastrophic. Therefore, when both solutions are viable, designers will prefer natural compensation.
The wall of the expansion joint is thin, making it prone to leakage, and its wave pattern provides limited compensation
Personally, I think it’s about cost control. The manufacture of expansion joints is influenced by the physical and chemical properties of the medium, as well as operating pressure and temperature. The cost of production can range from tens of thousands of yuan for those that are inexpensive to several million yuan for more expensive ones, and there are also many limitations regarding their application. For example, with these steam pipelines, most of them don’t seem to be useful; what is commonly used are optimized bends to counteract thermal stress. Don’t get stuck on certain things.
Expansion joints are prone to leakage, and this type of leakage involves pipe rupture; we have experienced such incidents several times here, with hydrochloric acid pouring out in a waterfall-like flow all at once. Even if a pipe leaks, it wouldn’t leak like this.