2 replies to this topic

[PME]

Rating of tappings for Temperature / Pressure connections should be same as that of associated piping class or can be higher than connected piping . Pl. clear the misconception

Regards
PME

[Andrei]

For sure all the instrumentation connections should be pressure/temperature rated at least as the associated piping/equipment. There are cases, especially at low equipment pressure ratings, when instrumentation ratings exceed the associated equipment. This is simply from manufacturing standpoint; certain instrumentation is available only at high-pressure ratings. Or there are cases when a high temperature rating will require a high instrument pressure rating even when the process does not require it.

[kdal]

Just to elaborate a little on Andrei's point about high temperature instrumentation. Generally speaking instruments are supplied wth stainless steel flanges and generally speaking the flange rating for the instrument is specified to be the same as the parent process pipe to which it is connected (e.g. 600# SS instrument flange on to a 600# CS process flange). For the vast majority of cases this is just fine but do be aware that the flange limits (pressure and temperature) for SS are different (lower) than those for the same rating of CS. This becomes a concern if the design (or even operating) conditions are close to the flange limit for the CS pipe; in this case it is possible that the instrument will need to be a higher pressure rating than the parent pipe. Typically it is a concern a high temperatures where the design temperature is close to the flange limit.