This is not the first time I have “beat up” on excess flow valves and the reliance on them as a “safeguard” in a PHA or process design. Both EPA and OSHA are on record stating their displeasure of claiming these valves as a safeguard. Now don’t get me wrong, these devices WORK and WORK WELL when they are DESIGNED, INSTALLED, TESTED, and MAINTAINED per the manufacturer’s requirements… and here lies the problem. These valves MUST be included in the PSI – Safety Systems with the engineering (i.e. sizing) documentation, as well as reside in the MI program for inspection and testing. Here is some language from one of the top manufacturer of these safety valves and we can see that these valves require a LOT of attention, which many facilities are lacking…
Sizing and Location are ABSOLUTELY CRITICAL!
Our PSI documentation MUST include the location(s) of these valves and a rationale as to why these locations were chosen. NOTE: these locations should be in the engineering rationale for their locations AS WELL AS shown on the P&IDs. The size of the valve, as well as the piping BEFORE and AFTER the excess flow valve plays a CRITICAL role in their proper function. From the manufacturer…
A break or leak downstream of an excess flow valve that does not allow a flow equal to the valve flow rating will not actuate the excess flow valve and could result in a fire or explosion from leaking gas. Do not install the valve in any piping which tends to restrict the valve inlet. This may prevent the excess flow valve from closing.
In other words, one of the MAJOR FLAWS in this reliance on these valves is that they are sized improperly so even when we have a catastrophic piping failure, the valve will NEVER close! Or we have a break in the piping, but the break is NOT large enough to cause the excess flow needed to actuate the valve; however, the uncontrolled release from the piping creates a very hazardous condition (e.g. exceeds LEL or IDLH).
However, the excess flow valve’s closing flow rate must be less than the capacity of the LP-Gas or NH3 system in which the valve is being used. The flow rating of the piping, fittings, pump, valves, and hose on both the inlet and outlet of the excess flow valve must be greater than the flow rating of the excess flow valve. If branching, piping length, additional valves, reduction in pipe size, elbows, or other necessary components in the piping system create restrictions which reduce the flow rating to less than that of the excess flow valve rating, the valve will not give excess flow protection, and additional excess flow valves must be installed at these points.
Functional Testing BEFORE “Reliance” is REQUIRED
Manufacturer’s Testing requirements BEFORE installation…
Manually operate the excess flow valve’s poppet before installation to assure parts were not damaged in shipment or blocked with dirt or foreign material.
This should be called out in your maintenance procedure and included in your maintenance training.
Manufacturer’s Testing requirements AFTER installation…
After the excess flow valve is installed, the system should be tested for excess flow valve operation by simulating a break downstream in the system at the furthermost point being protected. To test the unit, pressure the system and then open a shutoff valve quickly at the farthest point in the piping that the excess flow valve is intended to protect. There should be a sudden decrease in flow, indicating that the valve has closed and is working properly.
TRICK… You’re replacing your excess flow valve and it is a Replacement In Kind so NO MOC or PSSR is done, what is your trigger to ensure this TEST AFTER INSTALLATION is done? This test is done using the HHC/EHS, so there will be an exposure (at least potential exposure) so do we have the PPE Hazard Assessment for this task, will you require a Line Break/ Process Opening permit for this process opening? Will the maintenance personnel conduct this test as part of the install or will operators perform this test before start-up of the system? PLEASE make sure the area is properly ventilated and meets all HAZLOC electrical installation requirements if your HHC/EHS is a flammable gas/vapor/liquid.
Maintenance Schedule for Inspection and Testing
Excess flow closure should be checked annually or on a regularly scheduled basis to ensure that the valve is still functional.
Do we have a listing of all our excess flow valves? Are they all entered into our CMMS with the manufacturer’s frequency of inspection/testing? Are we doing ANNUAL FUNCTIONAL TESTING of these valves? Do our records show they all “passed”? Have we defined a “Pass/Fail” flow rate for these valves?
Excess flow valves are non-repairable. Replace non-functioning valves.
Is the business prepared to EMPTY the process and make necessary replacements when a valve fails its annual test? The process is LIVE when doing these functional tests, but when we find a valve that fails to function as designed, how long do we permit the process to operate before replacing the failed safety device?
Valves MUST be included in the applicable SOP as a “safety system”
These valves are unique and many operators may NOT know of their presence, their function, nor their limitations! The SOP and training should make it VERY CLEAR that an excess flow valve does NOT stop the flow of the HHC/EHS 100%. It is merely is intended to prevent an uncontrolled flow, preventing the emptying the entire contents of the vessel/container. As the manufacturer makes clear, these valves have limitations that personnel MUST be aware of…
Because of the bleed that permits the valve to equalize itself, a small amount of leakage will continue after the excess flow check closes.
After the excess flow valve closes, the leakage through the equalizing hole must be controlled or a hazard can be created. For this reason, the operator must be familiar with the system shutoff valves and close the system if an emergency occurs.
In other words, activation of an excess flow valve is NOT an “emergency shutdown procedure”!!!!! We must still close valves that will isolate the leak, whether that is done manually in the field or via a control panel, but the closing of the excess flow valve is merely the TRIGGER to ACTIVATE EMERGENCY SHUTDOWN procedures.
So as we can see, these valves are NOT “maintenance free” and if we plan to claim them as a safeguard we need to have the engineering basis, the PSI documentation, their inclusion in the applicable SOP(s) and training for operators, they have to be in a formal MI program inspection and testing program that includes maintenance procedures, and it would be a very good idea to ensure there is a PSSR line item and/or Start-Up procedure(s) that would require them to be functionally tested when a new one is installed or replaced. Then and ONLY THEN should we even consider claiming these devices as “safeguards”. So when was the last time you functionally tested your excess flow valve(s)???
Source for Manuafcturer’s Requirements: http://www.documentation.emersonprocess.com/groups/public/documents/instruction_manuals/d450008t012.pdf