SW / Flanged valve in refinery piping

The answer to your question is both "Yes" and "No"!

"Flanged valve should be used for maintenance purpose irrespective of size & service at: " Yes, if the Line class and the size is flanged. No if the size is too small to be flanged (Screwed or Socket-Weld).

1) At point of insulation break (generally at valves) Same answer applies here.

2) At bypass Same answer applies here.

3) At point of spec break viz. change in rating , corrosion allowance , change in piping material, etc. Same answer applies here.

4) Where spectacle blind is provided close to valve. Same answer applies here. If you are putting in a Spec Blind in a small line (2" /50mm or smaller) you keep the screwed or socket-weld valve and only add a pair of flanges not a more expensive flanged valve.


Pl. give info about it & clear my doubts regarding this. I hope this will help.