PSV & HIPPS Setting 1

[Alizium]

In my plant at distillation column there is HIPPS as well PSVs. Both have same set point. If the high pressure value reaches to the set point of HIPPS at the same time PSV will also act. There are other two columns in the plants both having HIPPS as well as PSVs but the HIPPS value is comparatively less than the PSV set point. I want to know the reason or logic for the first one where HIPPS and PSV has same set point. Is there any process safety reason behind that to keep the same value.

 

[LittleInch]

Someone chickened out in the first instance.

Usually a HIPPS is when you can't install a PSV because you're in the middle of no where or you can't deal with the volume of material coming out of the PSV safely.

Setting a PSV, which has a ??% under tolerance at the same as a HIPPS which is usually pretty tight on set point (~1-2%) on the face of it makes no sense.

But changing things without knowing why or without doing a MoC or HAZOP on the item is not good practice. See if you can dig up the SIL assessment which should have been part of the setting and approval process to install a HIPPS



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[RVAmeche]

I haven't directly dealt with a HIPPS system, but I have dealt with SIL rated interlocks and credits from a PHA.

Without knowing the details of your plant it's possible both types of systems were installed so the system would have the proper number of "credits" and to be considered a low risk safety issue. If your plant has done a PHA or Hazop, I'd recommend trying to find out who conducted it and the outcomes related to your plant so you can have some background information.

Without any details I would've assumed the HIPPS set point would be lower (disable whatever is causing pressure) and then the PSV set point would be a bit higher (but still at/below the max design pressure). The reason being you'd prefer the HIPPS to do its job and not have the PSV go off since that involves paperwork and other headaches.

Is this some sort of reactor or exothermic reaction where merely shutting down the pressure source (heat input, pump, etc) won't necessarily stop the pressure from building?

 

[LittleInch]

That's a good point given we know very little (i.e. nothing) about your process.

I'm more familiar with pressure breaks protected by a HIPPS where there isn't any chemical reaction or process, just pressure and the safe operation is simply turning off the pressure source (usually a high pressure pipeline or oil / gas well in my world).

but setting any trips, alarms and multiple devices very close to each other in pressure terms isn't normal practice IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EmmanuelTop]

There could be multiple overpressure scenarios for the system. I would say the only logical explanation for these two devices to have identical set point is either:
1) HIPPS does not cover all sources of overpressure, and PSV is there to take care of the unprotected source flow.
2) Somebody made a mistake and introduced identical set points for both.

Dejan IVANOVIC
Process Engineer, MSChE