13 replies to this topic

[rohollah]

Dear experts

As per API 526 sixth edition 2009,
cold differential test pressure=set pressure+manufacturer recommended temperature correction
my question is that,which temperature should be considered?
operating temperature,or relieving temperature?

regards
Rohollah

[ankur2061]

Rohollah,

I just checked out Appendix-B of API STD 526 where "Cold Differential Test Pressure" is defined. My interpretation of temperature correction is based on the relieving temperature at the inlet of the relief valve and not on operating temperature since the definition clearly states that:

The pressure at which the pressure relief valve is adjusted to open on the test stand

Regards,
Ankur.

.

[fallah]

I just checked out Appendix-B of API STD 526 where "Cold Differential Test Pressure" is defined. ....

Just minor correction: Appendix-A included above statement...

[rohollah]

in terms of backpressure correction, which backpressure should be considered?
superimposed or built up backpressure?

regards
Rohollah

[ankur2061]

Rohollah,

The definition is clear. Cold differential test pressure is when the relief valve opens on the test stand. On a test stand the relief valve is open to atmosphere, so the total backpressure is the sum of the superimposed backpressure (0 barg) plus the built-up back pressure.

Regards,
Ankur

[fallah]

in terms of backpressure correction, which backpressure should be considered?
superimposed or built up backpressure?

Rohollah,

It depends on the valve type:

-For conventional PSV it is just needed to consider correction for constant (or maximum variable) superimposed back pressure. Then, because in these valves in any case the build-up back pressure should be lower than allowable overpressure, no need to consider build-up back pressure in back pressure correction factor.

-For balanced bellows and pilot operated PSV's in the cases in which the build-up back pressure might increase the total back pressure such that exceeded the acceptable back pressure limits, then back pressure correction should be included build-up back pressure.

Fallah

Edited by fallah, 11 July 2012 - 10:18 PM.

[rohollah]

Fallah

First of all thanks for your good explanations.
it would be appreciated if you give me any reference for what you mentioned.

regards
Rohollah

[fallah]

it would be appreciated if you give me any reference for what you mentioned.

Rohollah,

It is logical result could be got from PSV fundamentals along with the conditions at PSV test on relevant stand. If you have any doubt on my explanations let's know to explain a little bit more.

Fallah

Edited by fallah, 12 July 2012 - 12:49 AM.

[rohollah]

in terms of backpressure correction, which backpressure should be considered?
superimposed or built up backpressure?

Rohollah,

It depends on the valve type:

-For conventional PSV it is just needed to consider correction for constant (or maximum variable) superimposed back pressure. Then, because in these valves in any case the build-up back pressure should be lower than allowable overpressure, no need to consider build-up back pressure in back pressure correction factor.

-For balanced bellows and pilot operated PSV's in the cases in which the build-up back pressure might increase the total back pressure such that exceeded the acceptable back pressure limits, then back pressure correction should be included build-up back pressure.

Fallah

Fallah
what do you mean by"in the cases in which the build-up back pressure might increase the total back pressure such that exceeded the acceptable back pressure limits"
does it mean,build-up back pressure should be considered in balanced bellows psv ,when back pressure>50% set pressure?

[fallah]

what do you mean by"in the cases in which the build-up back pressure might increase the total back pressure such that exceeded the acceptable back pressure limits"
does it mean,build-up back pressure should be considered in balanced bellows psv ,when back pressure>50% set pressure?

Rohollah,

I meant when, let say, build-up back pressure may increase total back pressure for balanced bellows higher than 30% of the set pressure and for pilot operated higher than 50% of the set pressure.

Fallah

[rohollah]

Fallah

As per API 520 part1 seventh edition- 3.3.3.2.1
max allowable back pressure for balanced psv is 50% set pressure.
but you mentioned 30%?

regards
Rohollah

[fallah]

As per API 520 part1 seventh edition- 3.3.3.2.1
max allowable back pressure for balanced psv is 50% set pressure.
but you mentioned 30%?

Rohollah,

I did want to clarify the concept. If you follow the API 520, you can get the value specified there.

Fallah

Edited by fallah, 13 July 2012 - 05:43 AM.

[rohollah]

Fallah

Thanks for your help.
should temperature correction be considered for open bonnet psv?

Rohollah

[fallah]

should temperature correction be considered for open bonnet psv

Rohollah,

As far as i know, there is no exception for temperature correction in bonnet type point of view.

Fallah