PSV relief pressure and set pressure 2

[rika kose]

I see a very strange PSV from a client.

The distillation column design pressure is 1.6 barg.
The column normal working pressure is 0.2 barg.
The PSV set pressure is 1.2 barg
PSV starts opening at 0.6 barg
The PSV fully opens at 1.5 barg.
Relief capacity at full open point is enough.

The PSV doesn't follow the normal consensus.
But there is no safety issue or operational issue.

Client wants to keep it this way. How to convince the client to correct PSV.

 

[shvet]

PSV starts opening at 0.6 barg
What do you mean? Simmering?

 

[rika kose]

Yes, simmering.

 

[The Obturator]

If the set pressure is 1.2 barg and the valve is simmering at 0.6 barg, then the valve is not working correctly.

Need more information from you;-
What valve is it - do you have a data sheet?
Design code, protected vessel? etc., etc.

Have you already discussed this with the supplier/manufacturer?


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[LittleInch]

Having a set pressure below the design pressure / MAWP is a client / operator decision.

Having "opening" or simmering at 50% below the set pressure is a fault with the valve or its sensing line.
Is this a spring relief or pilot operated relief?
How do you know its simmering?
Agree with The Obturator on need for more info.

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

 

[rika kose]

The system is from 50 years ago. 1970's.
So far, client hasn't found any design code or design document.

PSV is weight loaded.
PSV was tested. In the test they found the valve "first opening" literally translation is at 0.6 barg.

As the PSV fully opens at 1.5 barg lower than the MAWP. Relief capacity at 1.5 barg is greater than the faliure case relief flow.

Client thinks that there is not safety problem nor operational problem. the problem is that the PSV doesn't follow the engineering consensus/standards. why do they have to spend money to correct it?

 

[shvet]

So far, client hasn't found any design code or design document.
Guess:
- predicted temperature of vessel's wall under pressure during relief case is higher than PV design temp indicated at PV's nameplate
- PV design pressure was reduced as a result of a corrosion or a metal degradation or similar and Operator has clues concerned but does not share those
- PSV was designed to protect the pressure system element having the worst combination of design P&T during relief and this element protected is not the PV you have mentioned
- PSV fully opens at 1.5 and PSV reaches certified capacity at 1.6*1.1=1.76 barg
- PSV is designed for total liquid relief and 1.2:1.6 barg is related to PVSV elevation difference
Not always PSV set pressure = PV design pressure.

Note that "first opening" pressure ≠ simmering pressure. The opening is not the simmering.

 

[rika kose]

Thanks for the ideas.

Note that "first opening" pressure ≠ simmering pressure. The opening is not the simmering.

What are the differences?
Simmering is the relief valve begins to leak a little or the
valve is open only a few percent.
First opening or sometime it is called first leaking, that is also the point where PSV opens a little.

 

[shvet]

Opening - a test bench worker detects the seat is moving
Simmering - a test bench worker detects the seat is leaking

All seats leak when seat up/down forces ratio is below 1. The seat opens when up/down forces ratio is 1 or more.

API 520-1-2020
3.1.38
opening pressure
The value of increasing inlet static pressure at which there is a measurable lift of the disc or at which discharge of the fluid becomes continuous, as determined by seeing, feeling, or hearing.
3.1.57
simmer
The audible or visible escape of compressible fluid between the seat and disc of a pressure-relief valve that may occur at an inlet static pressure below the set pressure prior to opening.

 

[LittleInch]

Tends to indicate that after 50 years maybe either the seat or the seal need cleaning / machining or replacing. Resilient seals only last so long before they become stiff and inflexible.

Got any photos, drawings or anything else?

but if it's not going off and loosing product what's the issue here? If it needs to it clearly go off before you even get to MAWP so no safety issue there.

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

 

[rika kose]

Thanks Shvet for the info.

 

[GD2]

OP,
The valve surely don't meet the setting standard (Example: API 520-I). On the opening pressure of 0.6 barg, I have doubt on it. Typically, the valve has to be leak tested at 90% of 1.2 barg = 1.08 barg, which means the valve should be leak tight till 1.08 barg. Opening at 0.6 barg doesn't make sense.

Are the pressures you have provided CDTP or at actual operating conditions? Distillation columns are usually at higher operating temp. Setting PSV at a work bench in ambient condition will require compensation for both differential pressure and temperature multiplier.

As for your other question,why Client wants to correct it - either required to comply to local safety regulation or Insurance or both.


GDD
Canada

 

[The Obturator]

The valve being discussed, is a weight loaded valve of 50 years service. It is not in the scope of API-520 or ASME VIII. We really need the full detail of the application to comment further. Note also that such a weight loaded safety valve will require much more than 10% overpressure to attain full lift. These designs simmer forever. If you ask me, this needs swapping out to something more modern that meets current standards (and plant insurance underwriters). ISO-4126-1 Is your most appropriate specification to follow.


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[georgeverghese]

Agreed, a relief valve that cracks open at 50% of set pressure is probably a tank type safety valve, not an ASME Div 1, Sect 8 PSV. Or it could be similar to the integral relief valves that are fitted on pumps.

If the column is designed to ASME, then switch out to an ASME approved PSV. Using any other type of relief valve is not recognised as a Code compliant safety valve.

 

[rika kose]

Thanks everyone for the valuable comments