7 replies to this topic

[KINGMOON]

I am currently working in Indian Oil Corporation Limited, Mathura Refinery. My specific query / confusion is:

1.0> Is it mandatory that for fire-case design, there should always be only a single PSV (with no stand-by)? Is there really no provision for taking a stand-by PSV in fire case?? What is the basis for such a rigid rule??

2.0> All EPCM / Designers quote API-RP-520 in support of this. However I have read API-RP-520, Section 4.2.3. I have also seen section 4.2.3.4 which states "supplemental valves are used only in addition to valves sized for operating (non-fire) contingencies. It is not clear whether a "supplementarl" PSV means a "stand-by" PSV. Can anyone throw some light on this?

In fact apart from that single sentence, nowhere in section 4.2.3 it is stated that there should be a single PSV for fire case.

3.0> And if indeed the answer to the above question is yes, then kindly clarify what will be my safeguard if the only one (single) PSV provided malfunctions due to some reason (or some eventuality happens which necessiates it's maintenance) - does it mean for the single PSV I have to take a total shutdown of the unit??

4.0> What is the modern design trend worldwide in this regard - is it strictly as per section 4.2.3.4 of API-520??

[fallah]

I am currently working in Indian Oil Corporation Limited, Mathura Refinery. My specific query / confusion is:

1.0> Is it mandatory that for fire-case design, there should always be only a single PSV (with no stand-by)? Is there really no provision for taking a stand-by PSV in fire case?? What is the basis for such a rigid rule??
Saving the money! Actually the stand by PSV would provide but keeping in warehouse!
2.0> All EPCM / Designers quote API-RP-520 in support of this. However I have read API-RP-520, Section 4.2.3. I have also seen section 4.2.3.4 which states "supplemental valves are used only in addition to valves sized for operating (non-fire) contingencies. It is not clear whether a "supplementarl" PSV means a "stand-by" PSV. Can anyone throw some light on this?
It isn't a stand by PSV,but to be set at 110% of design pressure (or MAWP) as a supplement of main PSV in fire case or other expected external heat input,provided that permitted under equipment design code.
In fact apart from that single sentence, nowhere in section 4.2.3 it is stated that there should be a single PSV for fire case.

3.0> And if indeed the answer to the above question is yes, then kindly clarify what will be my safeguard if the only one (single) PSV provided malfunctions due to some reason (or some eventuality happens which necessiates it's maintenance) - does it mean for the single PSV I have to take a total shutdown of the unit??
Eventhough PSV has no significant role to protect equipment in fire case,it has a spare in warehouse causes having no worry about the maintenance.Actually in case of having spare for PSV the spare normally blocked by inlet blocked valve.
4.0> What is the modern design trend worldwide in this regard - is it strictly as per section 4.2.3.4 of API-520??
Not understand your mean accurately!

Edited by fallah, 06 August 2011 - 02:06 AM.

[Kunal_DNV]

Hi,

Can anybody please share wetted surface area formula for pig launcher?

Regards
Kunal

[Lowflo]

I am currently working in Indian Oil Corporation Limited, Mathura Refinery. My specific query / confusion is:

1.0> Is it mandatory that for fire-case design, there should always be only a single PSV (with no stand-by)? Is there really no provision for taking a stand-by PSV in fire case?? What is the basis for such a rigid rule??
No. The decision of whether to use an installed spare, shelf spare, or no spare at all is entirely for the user to make.

2.0> All EPCM / Designers quote API-RP-520 in support of this. However I have read API-RP-520, Section 4.2.3. I have also seen section 4.2.3.4 which states "supplemental valves are used only in addition to valves sized for operating (non-fire) contingencies. It is not clear whether a "supplementarl" PSV means a "stand-by" PSV. Can anyone throw some light on this? "Supplemental" means in-service valves that are installed to provide additional relief capacity. This statement is not talking about a spare PSV.

In fact apart from that single sentence, nowhere in section 4.2.3 it is stated that there should be a single PSV for fire case. How to replace a malfunctioning PSV? Policies vary from one company to another. Some install spare PSVs on most equipment, and some don't. If you don't have a spare, then you need to have a safe way to replace the on-line valve if it malfunctions. In some cases the vessel can be temporarily made safe for an on-line replacement without a total shutdown. Each installation should be evaluated separately to determine whether an installed spare is needed.

3.0> And if indeed the answer to the above question is yes, then kindly clarify what will be my safeguard if the only one (single) PSV provided malfunctions due to some reason (or some eventuality happens which necessiates it's maintenance) - does it mean for the single PSV I have to take a total shutdown of the unit??

4.0> What is the modern design trend worldwide in this regard - is it strictly as per section 4.2.3.4 of API-520??

[mhs]

Posted 08 August 2011 - 08:05 PM

KINGMOON, on 04 August 2011 - 11:50 PM, said:

I am currently working in Indian Oil Corporation Limited, Mathura Refinery. My specific query / confusion is:

1.0> Is it mandatory that for fire-case design, there should always be only a single PSV (with no stand-by)? Is there really no provision for taking a stand-by PSV in fire case?? What is the basis for such a rigid rule??
No. The decision of whether to use an installed spare, shelf spare, or no spare at all is entirely for the user to make.

2.0> All EPCM / Designers quote API-RP-520 in support of this. However I have read API-RP-520, Section 4.2.3. I have also seen section 4.2.3.4 which states "supplemental valves are used only in addition to valves sized for operating (non-fire) contingencies. It is not clear whether a "supplementarl" PSV means a "stand-by" PSV. Can anyone throw some light on this? "Supplemental" means in-service valves that are installed to provide additional relief capacity. This statement is not talking about a spare PSV.

Do u mean 'additional valve' is just to have large capacity relieving?
or they are sized for other scenario than the main psv?
and do they have different overpressure i.e. main psv is 121% set pressure for fire case and suplimentary psv for other than fire case at 110% of set pressure?


In fact apart from that single sentence, nowhere in section 4.2.3 it is stated that there should be a single PSV for fire case. How to replace a malfunctioning PSV? Policies vary from one company to another. Some install spare PSVs on most equipment, and some don't. If you don't have a spare, then you need to have a safe way to replace the on-line valve if it malfunctions. In some cases the vessel can be temporarily made safe for an on-line replacement without a total shutdown. Each installation should be evaluated separately to determine whether an installed spare is needed.

3.0> And if indeed the answer to the above question is yes, then kindly clarify what will be my safeguard if the only one (single) PSV provided malfunctions due to some reason (or some eventuality happens which necessiates it's maintenance) - does it mean for the single PSV I have to take a total shutdown of the unit??

4.0> What is the modern design trend worldwide in this regard - is it strictly as per section 4.2.3.4 of API-520??

[mhs]

2.0> All EPCM / Designers quote API-RP-520 in support of this. However I have read API-RP-520, Section 4.2.3. I have also seen section 4.2.3.4 which states "supplemental valves are used only in addition to valves sized for operating (non-fire) contingencies. It is not clear whether a "supplementarl" PSV means a "stand-by" PSV. Can anyone throw some light on this? "Supplemental" means in-service valves that are installed to provide additional relief capacity. This statement is not talking about a spare PSV.

Do u mean 'additional valve' is just to have large capacity relieving?
or they are sized for other scenario than the main psv?
and do they have different overpressure i.e. main psv is 121% set pressure for fire case and suplimentary psv for other than fire case at 110% of set pressure?

[fallah]

mhs,

Supplemental valve is used in addition to valves sized for non fire scenarios to provide relieving capacity for an additional hazard due to exposure to fire or other external heat sources.

The set pressure of a supplemental valve for fire shall not exceed 110% of MAWP.

Fallah

[Raj Mehta]

Sorry to reply late on this discussion. I am reading API 520, and ust putting forth my understanding and some doubts on the topic. I would really appreciate if some one can correct me, wherever I am wrong.

 

Say there are 3 valves

1. Valve1: Set pressure: 100 , accumulation / overpressure = 10% = 110, Relieving pressure = 110 (If only single valve is used) and = 121 (if multiple valves are used) 
2. Valve 2: Set pressure = 105, overpressure = ?, Relieving pressure = 116 ??
3. Valve3: Set pressure = 110, overpressure = Maximum relieving pressure = 116 ( non fire caese) & 121 (fire case) 

I believe the working is like, the first PSV will start to open up at 100, and opens up fully as the pressure rises till 110. At 105, the second PSV starts to open, and at 110 all other PSV's start to open. If the PSV's are to be designed for non-fire case scenario, then the maximum relieving pressure for all the additional PSV (except the first PSV) would be 116% MAWP. If its designed for fire case, all the  additional PSV will have maximum relieving pressure of 121% instead of 116%.      Right ???

 

Additional PSV are needed if the relieving capacity is very high ? Is one PSV sufficient ? But i guess the size of that PSV would be very large then, hence we go for multiple PSV ?

 

 

Doubts: 

• Why are there 2 values for Maximum relieving pressure as for fire contingency & non fire contingency 
• Multiple valve means ?? (all valves excluding single valve) ?

 

 

*NOTE: Ref. Figure 1, API 520, Part-I, 6th Edition

Edited by Raj Mehta, 16 April 2013 - 12:08 AM.