API 576 Question

[SAFTENG]

In API Recommended Practice 576 - Inspection of PRD's, Section 6.1.1 it talks about a "stop valve". It states

"When a block valve is provided between a vessel's only relief valve and the header the valve discharges into, the block valve shall be so arranged that it can be locked or sealed in either the open or closed position. The block valve shall be locked or sealed in either position by an authorized person only. If the block valve is to be closed while the vessel is in operation and the vessel has no other relieving device, the authorized person shall constantly monitor the operations and shall lock or seal the block valve in the open position before leaving. This valve should not be closed while the vessel is in operation unless a STOP VALVE is on the inlet side of the safety relieving device and is first closed".

What the heck is this saying? What is a "stop valve"? This section makes it sound like there are TWO (2) valves between the vessel and relief protection. Is this so? Please help!

Bryan

http://www.SAFTENG.net

 

[farshi]

hi mr. bryan

my idea about this subject is like that:
1.if the blocked vavle is in outlet of safety releif valve
during operation it should not closed at any time,if one time you close it, operator should close the inlet valve(stop valve)first,and then there is a standby for safety valve system,should be on service.it is equiped by inlet and outlet valve.
2.in some time if one safety valve is considered ,the outlet valve may equipped with bypass line.
3.in some system outlet valve is not considered.
yours truly
farshia@nioc-ripi.org
amir farshi


amir farshi
farshia@nioc-ripi.org

http://www.nioc-ripi.org

 

[ElderX]

The Sept. 1992 Edition of 576 has a sketch Figure 34 on page 25 maybe this will help. A picture is worth.....