Maintenance Intervals - Pilot Operated RV's

[lc987]

What is the maximum maintenance interval you would recommend for pilot operated relief valves in clean butane service?

API RP 576 provides interval guidelines with 10 years as the maximum. This may be okay for conventional spring loaded RV's but seems excessive for pilot operated RV's that are more sensitive due to pluggage of the inlet filters and closer tolerances.

 

[dcasto]

Only you can decide this. Here's an approach we use. It's a risk managemnet based one. The priciple is similar to that of a PHA. We set up a table that has grades or rankings for the risk associated with the item that requires periodic inspections. We ask questions like:

1 Corrosiveness of fluid on scale 1 to 10
2 Pressure in psig dived bey 100 (to get a 1 to 10)
3 Temperature range with 100 =1, >500=10 < -200 = 10.
4.Velocity ranges 1 to 10.
5. Toxicity, flash point, errosion, time sence last opening or failure, vibration, ect.
6. The we do the same with midigational items, use of corrosion inhibitors, Maop is 4 time normal conditions, Other controls, ect.

Next we risk rank the responces by applying a factor, like corrosive results gets multiplied by 4 and toxic by 10, but velocity is multiplied by 1. WE then add up the impacts, subtract the midigations.

You end up with a set of values that range from maybe 25 to 500. The 25 would be a cooling water system and the 250 was an H2S rich stream on a compressor.

From our maintenance people prospective we know that the H2S rich gas relief valve has failed and we need to inspect it annually and the water has never so it is every 10 years. We partion of the ranges of values for the 1 to 10 year range.

Now you have a defendable risk management plan that includes input from all levels in your company. It takes some subjective risks and makes them objective. Or you can set very measureable values too that will make it all objective. For example vibration, 1 mil/sec =3, 5 mill/sec = 7 .05 mil/sec = 1.

 

[BenThayer]

it is whatever you decide based on that system's inspection history per API.

"the intervals between pressure relief device testing or inspection should be determined by the performance of the devices in the particular service concerned."

dcasto gives a reasonable way to help guide and implement your decisions. but it is still your decision.

 

[JLSeagull]

For offshore applications, API 14C recommends testing all safety devices and systems at specified regular intervals - at least annually. This would apply to the pressure safety relief valves. Shutdown sensor testing is more often, quarterly for electronic transmitters and monthly for discrete devices.

Table D-2 includes a safety device test procedure. PSV set pressure tolerances are plus or minus 2 psi (14 kPa) for pressure up to and including 70 psi (480 kPa), and plus or minus percent for pressure above 0 psi (480 kPa). PSV test procedures in the table include external pressure test and bench test methods.