For which type of pressure is threaded pipe and screwed connections generally used?

Threaded pipe and screwed connections are predominantly used for low and moderate pressures due to the limitations of the connection methods involved. These types of connections rely on the mechanical engagement of threads to create a seal, which can be effective for applications where pressures do not exceed certain limits.

In low to moderate pressure systems, the potential for leaks is relatively low, and do not require the strength that welded or flanged connections may provide, which are better suited for high-pressure applications. As the pressure increases, the stresses on the threads and the likelihood of failure through thread stripping or disconnects also increase.

Moreover, threaded connections can be challenging to make leak-proof at high pressures and in vacuum systems, as they may not withstand the extreme forces or structural integrity needed. This makes them less desirable for such applications, reinforcing the idea that low and moderate pressure environments are where threaded pipe and screwed connections find their optimal use.