By dbigkahunna
Date 03-17-2014 23:23
Edited 03-17-2014 23:31
B31.8 is for gas and B31.4 deals with liquid pipelines.
The break from the pipeline to the plant/compressor which will be under B31.3 will USUALLY be at a valve. If it is a weld on valve, one side of the valve is covered under 1104 and the other weld is B31.3. In some places it is a fence. And yes you can have one welder welding DH on one end of the joint and another welder welding UH on the other end.
If this O Let will be the break there should be a valve on top of the O Let and then everything behind that valve will be considered "plant" work under B31.3. When the flow comes back to the pipeline, there will be another O Let downstream from the first one with a block valve between them.
When the valves on the O Lets are open and the block valve closed the flow goes to the "plant" or compressor station. When the valves on the O Lets are closed and the block valve opened the flow bypasses the plant or compressor station.
When it hits the valve again everything behind it is B31.3 and on the other side of the valve it goes back to B31.4 or .8
When you read B31.4 and B31.8 it will give the NDT requirements, etc, based on the location of the pipeline.
A line in a high consequence area will require more NDT than a gathering line out in a pasture.