(3) Stop valves may be installed between a pressure relief device and the operating vessel for the purposes of inspection, repair and/or replacement of the pressure relief device. Where stop valves are installed, the employer shall develop, implement, and maintain a written plan containing all of the following:
(A) Procedures to ensure that stop valves are open and locked or sealed during normal operations and are not to be closed except by a qualified person(s).
NOTE: In the case of multiple relief device installations having spare capacity or spare relief valves, the stop valve can be closed on the inactive relief valves providing sufficient system relief capacity is maintained.
(B) Procedures to minimize the frequency of closing stop valves while the vessel is in service. Stop valves shall remain open and locked or sealed until a replacement pressure relief device is available for installation.
Exception: Stop valves may be closed for emergencies such as pressure relief device failure.
(C) Procedures to ensure that a replacement pressure relieving device or needed replacement parts are readily available prior to closing the stop valve and removing the pressure relief device. An index for the location of all stop valves subject to this section shall be maintained.
(D) Before the removal of a pressure relief device from operating equipment, facility management shall review and approve a written operations plan for closing the stop valves. The plan shall incorporate, at a minimum, the following elements:
1. An engineering review to ensure that no increase in the capacity, pressure, severity, and/or operating condition of the unit or vessel will affect the safety of employees or equipment while the pressure relief device is out of service;
2. Provisions for written notification and operational procedures to unit controllers, operators and other affected personnel, including the safeguards and estimated time the valve will be out of service;
3. Identification of the functional position(s) or employees having knowledge of the operating equipment and pressure-relieving device(s) authorized to approve closing a stop valve; and,
4. Identification of the qualified person(s) or functional position(s) authorized to actually close and then reopen a stop valve.
(E) A written overpressure relief plan for each safety relief device shall be developed prior to closing the stop valve. The plan shall include:
1. The means by which overpressure-relief protection will be provided during the time that the pressure relief device is out of service;
2. The procedures to be followed to minimize the time that the stop valve will be closed;
3. The operating conditions, limitations, and other safety measures which are required to be observed to protect employees and equipment; and,
4. In the event that the plan requires a standby person to manually operate a vent to the atmosphere, a replacement safety relief valve shall be available for installation prior to closing the valve. Employees shall be protected from hazards as identified by Article 10 of the General Industry Safety Orders.
(F) The written overpressure-relief plan shall be made available to the Division upon request during the course of the work operation to which it applies.
My experience is no procedure for block valves in front of PSV actually works in the field. I can't tell you the number of times I've seen closed block valves in front of PSVs, no matter what "procedure" was in effect.
I use plastic tie wraps (use to use stainless steeltags and before that chains and locks). There is a tag or color code that state where the valve is sealed open or closed. During quarterly LDARS (fugative emissions testing), the sealed valves are inspected and the seal status is recorded. This gets them inspected and verified by a qualified person every quarter.
All the other engineering review stuf is common sense about having something in place while the valve is shut and the PSV is inspected.
The tags are also a good idea on any criticle valve, like ones under pressure transmitters.
