StevenHPerry
Mechanical
- Sep 15, 2006
- 210
What do you typically do downstream of vent & drain valves on high pressure & high temperature lines?
Within B31.1, paragraph 114.2.1 restricts or prohibits threaded connections in these circumstances.
A pipe spec I’m dealing with includes threaded nipples and caps which are intended for use downstream of drain / vent valves. The header is, for argument’s sake, 926F and 1501psig, so threaded components are not allowed in the main process.
One line of reasoning is that immediately downstream of the drain/vent valve the expected conditions are below 925F and at ambient pressure, so the TOE nipple and cap are not ‘expected’ to see the main line’s conditions. However, we do not want to put P&T breaks across every vent/drain valve and changing pipe specs is also too cluttered. A typical detail was suggested, but is outside company policy.
A second line of reasoning is that valves fail or someone could open these readily-accessible valves and expose the downstream components to the full conditions of the header. Rather than putting threaded components here, a socketwelding arrangement is suggested that will be sealed up after hydro, with dye-pen or other suitable NDE testing applied to the final weld.
Neither option seems ideal. How do you do it?
Within B31.1, paragraph 114.2.1 restricts or prohibits threaded connections in these circumstances.
A pipe spec I’m dealing with includes threaded nipples and caps which are intended for use downstream of drain / vent valves. The header is, for argument’s sake, 926F and 1501psig, so threaded components are not allowed in the main process.
One line of reasoning is that immediately downstream of the drain/vent valve the expected conditions are below 925F and at ambient pressure, so the TOE nipple and cap are not ‘expected’ to see the main line’s conditions. However, we do not want to put P&T breaks across every vent/drain valve and changing pipe specs is also too cluttered. A typical detail was suggested, but is outside company policy.
A second line of reasoning is that valves fail or someone could open these readily-accessible valves and expose the downstream components to the full conditions of the header. Rather than putting threaded components here, a socketwelding arrangement is suggested that will be sealed up after hydro, with dye-pen or other suitable NDE testing applied to the final weld.
Neither option seems ideal. How do you do it?
