PSV testing

[suttsy]

Hi,
Our plant has a heating hot water loop system & a chilled water loop system. They both have PSV's which are ever highly unlikely to lift, as the feed pumps are under rated.
We do not have a planned shutdown in motion on this site.
My question is:
Is there a statuory law regarding the testing of these PSV's on these water lines.
Any info would be appreciated.
This shutdown would have a big impact throughout the site.

 

[OilToil]

What are the overpressure scenarios? If you can mitigate those, do you need a PSV?

In a heated water loop, your overpressure source may not be the pumps, but rather heat input from the heater, or blocked flow and thermal expansion, or fire case on a vessel.

Same for the chilled side - what if the chilled side is shut in and warms up?

If you can mitigate these by stationing trained operators that know what action to take in case of overpressure, lock open valves, or use 'reliable' enough control systems, then it's up to you to prove it to your management, regulators, insurace etc.

Another thing to look at might be to install a PSV somewhere else in the system while the other one is out of service.
What are the consequences of overpressure?

 

[suttsy]

Thanks, for your reply OilToil.
We are currently reviewing this situation.
It's looking highly likely that these systems will have to be shutdown, as there are no isolation points to remove the valves.

 

[don1980]

If all you're protecting is this water piping, rather than a pressure vessel, then there's no legal requirement. You can choose to protect the pipe by use of operating procedures.

Since this is chilled water, I'm guessing the PSV was installed for thermal expansion protection. It's a good idea to keep the PSV, but you can implement procedural control to prevent overpressure until your next turnaround.

 

[suttsy]

Thanks don1980.
Our plant steam heats a hot water loop through heat exchangers.
There is no expansion tank on this loop, the water is circulated to 4 buildings for heating 24/7.
The PSV is 5bar rated.
The loop pressure 1bar constant.

 

[Duwe6]

Industry standard is 5-years normal, 10 years max for a Test & Reset on PRV's on innocuous systems. You've gotta be able to shut down for a couple of hours some time in 10-years. If not, how can you reapir pumps and valves?

Buy 2 matching spare PRV's, so both can be swapped out within a couple of hours. If that's too $$pricey for your management, buy 2 Rupture Disks with holders, and swap to those.

Additionally, most PRV shops can and will give same-day service if it is scheduled ahead of time. No new equipment, but you will need 18-24 hours of shut-down time [some time in 5 to 10 years]. It's not very tough to keep up with PRV's, if you plan them into unit maintenance.

 

[rocketscientist]

Although OSHA is murky on the subject of protecting pipe it is considered good judgement to do so for situations like thermal expansion of trapped liquid. In the pipeline world, these relief valves are called TRVs.

Wherever I'v worked, a 1-year inspection standard was required for critical relief devices. I believe OSHA requires this frequency for lethal service. In today letiguous society, if it explodes, burns, kills or spills --- resulting in mild irritation --- it should be treated as lethal service. That means steam, water is ok.

Where non-critical service is involved, like process water, corrosion is the enemy. What does your corrosion engineer say? 5-years might be too long. 2-years sounds about right for new service. If you're working with familar systems go with 5-years.