GlennWithTwoNs
Materials
- Apr 25, 2023
- 1
Good day,
As a contract integrity inspector throughout the oil & gas industry, I've witnessed several designs of reciprocating compressor skids (mostly for natural gas dehydration and pressure increases). I am responsible for verifying over-pressure protection of the pressure vessels as part of regulatory inspections.
Process flow through a typical gas compressor skid is as follows:
Inlet Separator - Suction Scrubber - Suction Bottle (Dampener) - Compressor Throw - Discharge Bottle - Aerial Aftercooler ->Repeat for 2nd stage, etc.
Typically, the inlet separator will have a PSV, the suction scrubber will have a PSV, and a PSV will be installed on the piping between the discharge bottle and cooler.
It's understood that the discharge piping PSV will protect the 1st stage discharge bottle, cooler, as well as the 2nd stage suction scrubber and suction bottle.
Also, the suction scrubber PSV will protect the suction scrubber and suction bottle. This design is great, over-pressure protection for each vessel is straight-forward.
Several compressor skids (for which the designs have been approved by various engineers before I came along) have the inlet separator and PSV in a different skid, connected by common piping with the compressor skid. In this design, the suction scrubber does NOT have a PSV, and there is a skid-isolation (block) valve in between the inlet separator and suction scrubber.
My understanding of ASME VIII is that this block valve is required to be locked open to allow an unobstructed flow path between the suction scrubber and it's over-pressure protection.
I also understand that during normal operation, the 1st stage discharge PSV would protect the whole 1st stage from over-pressure. However, if the compressor was idle or malfunctioning, I believe the suction scrubber would be vulnerable.
Can someone set me straight?
Appreciate it,
Ryan
As a contract integrity inspector throughout the oil & gas industry, I've witnessed several designs of reciprocating compressor skids (mostly for natural gas dehydration and pressure increases). I am responsible for verifying over-pressure protection of the pressure vessels as part of regulatory inspections.
Process flow through a typical gas compressor skid is as follows:
Inlet Separator - Suction Scrubber - Suction Bottle (Dampener) - Compressor Throw - Discharge Bottle - Aerial Aftercooler ->Repeat for 2nd stage, etc.
Typically, the inlet separator will have a PSV, the suction scrubber will have a PSV, and a PSV will be installed on the piping between the discharge bottle and cooler.
It's understood that the discharge piping PSV will protect the 1st stage discharge bottle, cooler, as well as the 2nd stage suction scrubber and suction bottle.
Also, the suction scrubber PSV will protect the suction scrubber and suction bottle. This design is great, over-pressure protection for each vessel is straight-forward.
Several compressor skids (for which the designs have been approved by various engineers before I came along) have the inlet separator and PSV in a different skid, connected by common piping with the compressor skid. In this design, the suction scrubber does NOT have a PSV, and there is a skid-isolation (block) valve in between the inlet separator and suction scrubber.
My understanding of ASME VIII is that this block valve is required to be locked open to allow an unobstructed flow path between the suction scrubber and it's over-pressure protection.
I also understand that during normal operation, the 1st stage discharge PSV would protect the whole 1st stage from over-pressure. However, if the compressor was idle or malfunctioning, I believe the suction scrubber would be vulnerable.
Can someone set me straight?
Appreciate it,
Ryan
