7 replies to this topic

[ogpprocessing]

Dear All,

API 526 provide some tables of "Outlet Pressure Limit" for safety valves based on PSV orifice type and PSV type itself.

Now my questions are:

1.What is the application of these outlet pressure limit values?

2. Each PSV has a specific back pressure constraint value based on PSV type and set pressure for example 10% for conventional or 40% for balanced type and etc. Now when doing flare network simulation, is it necessary for process engineer to consider API 526 values in excess of those values recommends by API 520 (10% or 40% and etc)?

Edited by ogpprocessing, 02 September 2010 - 06:12 AM.

[fallah]

Ogpprocessing,

1-"Outlet pressure limit" is the limitation value (in temperature of 100F) the PSV may subject to it and basically extracted from the pressure-temperature rating of the flanged valves as per ASME B16.34

2-The process engineer should specify maximum allowable back pressure of the PSV,and vendor to select the PSV shall check the back pressure value along with the relief temperature to meet the pressure limitations in API 526.

Regards

Edited by Art Montemayor, 02 September 2010 - 05:58 PM.

[ogpprocessing]

1-"Outlet pressure limit" is the limitation value (in temperature of 100F) the PSV may subject to it and basically extracted from the pressure-temperature rating of the flanged valves as per ASME B16.34

The outlet pressure limit values can only be used if they are updated based on real conditions. How to convert the outlet pressure limit values from 100F to actual relieving temperature?

2-The process engineer should specify maximum allowable back pressure of the PSV,and vendor to select the PSV shall check the back pressure value along with the relief temperature to meet the pressure limitations in API 526.

So you mean the outlet pressure limit values of API 526 should be used as MABP (maximum allowable back pressure limit) constraint of flare network simulation(one of the Flarenet software inputs data)?

[fallah]

The outlet pressure limit values can only be used if they are updated based on real conditions. How to convert the outlet pressure limit values from 100F to actual relieving temperature?

By using the pressure-temperature rating in the tables available in ASME B16.34
So you mean the outlet pressure limit values of API 526 should be used as MABP (maximum allowable back pressure limit) constraint of flare network simulation(one of the Flarenet software inputs data)?

No,you should consider back pressure limitations for stable operation of the PSV (10% of the set pressure for conventional,.....) and vendor shall check the outlet pressure limit value (the value corresponding to the relief temperature) of the selected valve be higher than the specified back pressure.

Edited by fallah, 02 September 2010 - 03:48 PM.

[ogpprocessing]

By using the pressure-temperature rating in the tables available in ASME B16.34

Is this part of vendor responsibilities?

No,you should consider back pressure limitations for stable operation of the PSV (10% of the set pressure for conventional,.....) and vendor shall check the outlet pressure limit value (the value corresponding to the relief temperature) of the selected valve be higher than the specified back pressure.

In my view both of API 520 and API 526 concerns regarding to back pressure are important and should be checked to ensure stable operation of PSV. So if the process engineer receives a feedback from vendor that they can not meet the outlet pressure limit values, this means that process engineer shall revise the flare network design and simulation in terms of maximum allowable back pressure constraint of API 526?

[fallah]

Is this part of vendor responsibilities?

Yes,but purchaser may also submit his proposed value and vendor would be requested to check.

In my view both of API 520 and API 526 concerns regarding to back pressure are important and should be checked to ensure stable operation of PSV. So if the process engineer receives a feedback from vendor that they can not meet the outlet pressure limit values, this means that process engineer shall revise the flare network design and simulation in terms of maximum allowable back pressure constraint of API 526?

API 520 looks at process piont of view and API 526 looks at piping point of view (a valve as an element of piping system).If vendor advise that the back pressure would pass the outlet pressure limit,process engineer have to recheck and revise the value.

[ogpprocessing]

If vendor advise that the back pressure would pass the outlet pressure limit,process engineer have to recheck and revise the value.

So as I did suggest in my earlier post as a general point, when doing flare network simulation the maximum allowable backpresssure constraint should be the smaller value between API 520 recommended value (from process perspective) and API 526 recommended outlet pressure limit value (from mechanical integrity perspective). Do you agree?

[fallah]

So as I did suggest in my earlier post as a general point, when doing flare network simulation the maximum allowable backpresssure constraint should be the smaller value between API 520 recommended value (from process perspective) and API 526 recommended outlet pressure limit value (from mechanical integrity perspective). Do you agree?

Agreed.