Set Point (PAHH) for High Integrity Pressure Protection System (HIPPS)

[NiravK]

For one of our Projects, High Integrity Pressure Protection System (HIPPS) to be provided to protect down stream low pressure piping in case of failure of upstream Pressure Control Valve (Failure OPEN).


Design Pressure at upstream of Pressure Control Valve: 63.5 Bar g
Design Pressure at down stream of Pressure Control Valve (after first isolation): 28 Bar g

Low pressure piping is supplymentry line for Compressor (Suction Pressure 20 barg, High Pressure Alarm Set Point = 26 Barg....one PSV is provided at KO Drum set at 28 Bar g).

PCV on high pressure line is always subjected to high pressure 40 Bar g. Due to existing flare capacity limitation...PSV can not be provided...therefore HIPPS is recommended.

At the down stream of PCV, Mokveld HIPPS is provided to close two ESDVs (at the upstream of PCV) within 2 sec. in case of Failure (OPEN) of Pressure Control Valve through 2oo3 PT signals.

HIPPS pre ALARM (PAH) and set Point (PAHH) is to be finalized..............Any suggestions..........

 

[hacksaw]

your pressure setpoints must be coordinated with the design pressures.

it is generally taken that without some sort of mechanical overpressure protection that the downstream piping and equipment must be designed for the maximum pressure expected.

 

[Guidoo]

Some years ago I have done some (simple) dynamic simulations to show that downstream pressure remains below design pressure (or 1.1xdesign pressure for short period of time), taking into account the dynamics of the HIPPS, as well as the system volumes, the small relief valve that is provided etc.

Did you check with Mokveld, they have quite some expertise in the area of HIPPS.

 

[ProPiper]

Agree with Hacksaw, a PSV is suggested in this situation. PSV set point shoud be your downstream mechanical design pressure. Make sure your operating pressure is less than 90% of the PSV set pressure. So you will not get PSV popup too often.

An alarm is also helpful, which should be set at the middle of the PSV set point and operating pressure.

 

[SeanB]

ProPiper I think you are missing the point here. The reason for the HIPPS system is that a PSV cannot be added because any relief would exceed the flare system capacity. On a recent project we added a HIPPS system for just this reason. At my last involvement on the project we had set the PAHH to trip the valves at 10% below the downstream design pressure - where you would normally set your PSV.

 

[NiravK]

At present, i have set 27 Bar g because Compressor suction high pressure alarm is 26 Bar g....and i think 10% below design pressure (28 barg) i.e. 25 Bar g will be at very conservative side and additionally working range of Compressor shall also be reduced.

I hope, this 1 Bar g allowance w.r.t design pressure of 28 Barg shall be adequate to take care the piping in case of incidental maximum operating pressure.

Sorry for misssing one relevant information....at the d/s of PCV.....design pressure is 51 Bar g for short length before joining to Low pressure (28 bar g) piping......

With the assumption that this high design pressure piping (short in length) will take care initial INCIDENTAL pressure surge....Pre set alarm at 26.5 Bar g and finally 27 Bar g to activate the HIPPS........

Guidoo.....please give me some clue for Dynamic simulation....

 

[Guidoo]

nirav2909,

.....please give me some clue for Dynamic simulation....

Well it's not so easy to explain in just a few words. Also I think that there are nowadays easier ways to do the dynamic simulations (e.g. by using Hysis or DinSym or similar packages).

Basically you make a mathematical model and use that to simulate some scenarios (e.g. downstream blockage). The heart of the model is a time dependent material balance of the downstream system. You also need flow equations to see how much gas flows into and out of the downstream system, gas law pV=znRT to convert moles into pressures and for the valves a relationship of valve Cv vs. valve opening or Cv vs. time.

We used a program called PSI to solve the equations, but you could also use other software such as Mathlab/Simulink. The simulation results were used convince the authorities that plant was sufficiently protected against overpressure.

You can find more about HIPPS in Norsok standard P-001. See

http://www.standard,no/petroleum/

 

[MortenA]

Nirav/Guidoo

Hysis is propably not so good for dynamic simulation of flow since it does not have a working model component for piping. I would recommend flowmaster for simulation of process piping. (gas or liquids but not multiphase)

Best regards

Morten