33 replies to this topic

[Afshin445]

Dear memebers,

I try to size a psv installed on water injection line.Two scenario can be considerd, for water thermal expansion.

1- Water expansion due to solar radiation
2- Water expansion due to Fire

As per API 521 for first scenario 3/4" x 1" psv size is enuogh, but for 2nd case we need at leat psv 3" x 3" size.My question is which PSV size I need to select for this application.

Thanks and regards

Edited by Afshin, 30 December 2011 - 02:46 AM.

[S.AHMAD]

Fire case does not apply to pipeline.

[Afshin445]

The PSV installed on Water Injection Filter on platform.

Edited by Afshin, 30 December 2011 - 03:06 AM.

[S.AHMAD]

For pipeline, only thermal expansion by sun radiation is being considered.

[Afshin445]

The filter can be exposed to fire because it close to production wells in wellhead platform.

[paulhorth]

Afshin,
Your first post said that the PSV is on the water injection LINE. Ahmad replied to that post.
Now you say you have a PSV on a filter. That is different.
For a PSV on the filter you should size it for the fire case, if the filter can be blocked in. Note that the PSV will be relieving steam not water, so you should think carefully where the discharge is routed, you do not want steam blowing around when the fire team is fighting the fire.

Paul

[fallah]

Dear Afshin,

Would you please submit a simple sketch of your system to clarify your query.

Fallah

[Afshin445]

Afshin,
Your first post said that the PSV is on the water injection LINE. Ahmad replied to that post.
Now you say you have a PSV on a filter. That is different.
For a PSV on the filter you should size it for the fire case, if the filter can be blocked in. Note that the PSV will be relieving steam not water, so you should think carefully where the discharge is routed, you do not want steam blowing around when the fire team is fighting the fire.

Paul

Paul
Sorry if I confused you and Ahmad.Actually PSV located in filter and filter installed in water injection line in wellhead platform.
I am agree with you, I need to consider fire case scenario, but PSV set pressure is 148.3 barg and releif temperature would be around 357 °C(with consideration of 21% overpressure) and I think this temperature is higher than filter material limit (C.S.).For this reason I only consider Thermal expansion due to solar radiation and fire when inlet/outlet filter isolation valves are close.
Do you agree with me?

Rgrds

Dear Fallah,

Please enclosed find simplified sketch.

Attached Files

•  sketch.xlsx   12.08KB   146 downloads

Edited by Afshin, 03 January 2012 - 06:21 AM.

[fallah]

Dear Fallah,

Please enclosed find simplified sketch.

Dear Afshin,

Nothing attached!

Fallah

[Afshin445]

Dear Afshin,

Nothing attached!

Fallah

Dear Fallah,

I attached again.

rgrds

Attached Files

•  sketch.xlsx   12.6KB   53 downloads

Edited by Afshin, 03 January 2012 - 08:56 AM.

[paulhorth]

Afshin,

Consider what will happen if the filter is blocked in and exposed to fire. Since it is full of water, the pressure will rise rapidly for a small increase in temperature, then the PSV will open for thermal expansion, releasing a small volume of water. The temperature will continue to rise, and the PSV will continue to discharge water, until it reaches 357 C when the water will boil and the PSV will discharge steam. The PSV must be large enough to do this without the pressure rising further. The temperature will not rise further until the filter has boiled dry.
BUT.....It is possible that at some temperature below 357 C, the vessel will become weak enough to crack or rupture at the 148 barg pressure. The water will flash into steam at atmospheric pressure leading to an explosion. Whether this happens depends on the material of construction and the yield stress vs temperature curve. In this event the PSV gives no protection and you should consider the following measures:

• deluge
• grated deck to prevent a pool fire
• location away from the wellheads to prevent impingement by a jet fire
• locked open isolation valves
• passive fire protection (not usually applied to water filters).

The size of the filter also makes a difference. If this is a relatively small in-line filter (as I guess from its application on a wellhead platform fed with treated injection water), then the explosion hazard is possibly small enough to be acceptable. More so, if the platform is not manned.
Paul

Edited by paulhorth, 03 January 2012 - 02:20 PM.

[S.AHMAD]

Dear Afhsin

1. Based on the drawing attached, what you are protecting is the filter, not the pipeline. TRV for pipeline is only applicable for block-in conditions.

2 As per ASME Code, all pressure vessels must be protected by PSV, at least TRV. The purpose of PSV is to protect the vessel from overpressure that lead to explosion.

3. Pipeline is normally considered destroy during fire

4. However, for some cases, you may need to do RISK ANALYSIS to justify any protection devices.

Edited by S.AHMAD, 03 January 2012 - 07:11 PM.

[Afshin445]

Afshin,

Consider what will happen if the filter is blocked in and exposed to fire. Since it is full of water, the pressure will rise rapidly for a small increase in temperature, then the PSV will open for thermal expansion, releasing a small volume of water. The temperature will continue to rise, and the PSV will continue to discharge water, until it reaches 357 C when the water will boil and the PSV will discharge steam. The PSV must be large enough to do this without the pressure rising further. The temperature will not rise further until the filter has boiled dry.
BUT.....It is possible that at some temperature below 357 C, the vessel will become weak enough to crack or rupture at the 148 barg pressure. The water will flash into steam at atmospheric pressure leading to an explosion. Whether this happens depends on the material of construction and the yield stress vs temperature curve. In this event the PSV gives no protection and you should consider the following measures:

• deluge
• grated deck to prevent a pool fire
• location away from the wellheads to prevent impingement by a jet fire
• locked open isolation valves
• passive fire protection (not usually applied to water filters).

The size of the filter also makes a difference. If this is a relatively small in-line filter (as I guess from its application on a wellhead platform fed with treated injection water), then the explosion hazard is possibly small enough to be acceptable. More so, if the platform is not manned.
Paul

Paul,

As per vendor data filter material is C.S. (SA 516 Gr.70) with supper duplex cladding. Also filter dimension is 710 mm(ID) x 3500 mm (Height).
If I follow your recommendation as above, do you think, it's need to size the PSV for fire case or only thermal expansion is enough?

Rgrds
Asfhin

[fallah]

Dear Afshin,

Nothing attached!

Fallah

Dear Fallah,

I attached again.

rgrds

Dear Afshin,

Please specify if the vessel can be isolated or not while it is exposed to fire.

Fallah

[paulhorth]

Afshin,
As I said,

The PSV must be large enough to do this without the pressure rising further.

That means, you should size the PSV for the fire case, steam relief. it won't cost a great deal more than for thermal expansion.

BUT....I repeat, this will not protect the vessel, if it could rupture below 357 C. You do need to consider this and make the check. The size that you give is quite large, in my view, containing well over a tonne of water, that's a lot of energy to be released when flashing into steam, so the explosion consequence is significant.
Can you answer these questions:

• Is the platform normally manned or unmanned?
• What fire protection systems are installed?

The answers do not change the sizing basis for the PSV but will help us undestand the risk of a rupture and the consequences.

Paul

[Afshin445]

Dear Afshin,

Please specify if the vessel can be isolated or not while it is exposed to fire.

Fallah

Dear fallah,

Yes, filter has isolation valves in inlet and outlet lines.

Afshin

Edited by Afshin, 04 January 2012 - 06:02 AM.

[Afshin445]

Afshin,
As I said,

The PSV must be large enough to do this without the pressure rising further.

That means, you should size the PSV for the fire case, steam relief. it won't cost a great deal more than for thermal expansion.

BUT....I repeat, this will not protect the vessel, if it could rupture below 357 C. You do need to consider this and make the check. The size that you give is quite large, in my view, containing well over a tonne of water, that's a lot of energy to be released when flashing into steam, so the explosion consequence is significant.
Can you answer these questions:

• Is the platform normally manned or unmanned?
• What fire protection systems are installed?

The answers do not change the sizing basis for the PSV but will help us undestand the risk of a rupture and the consequences.

Paul

Paul,

As I understand from your answer, PSV need to size for fire case scenario when PSV outlet is steam. In responce to your question I need to say, the platform is unmanned, it consist of normal fire & gas system and two monitores around production wells for fire fighting purpose.The firewater ring is dry and fire water is supplied from supply boat/barge in boat landing area during fire.

Afshin

Edited by Afshin, 04 January 2012 - 06:02 AM.

[fallah]

Dear fallah,

Yes, filter has isolation valves in inlet and outlet lines.

Afshin

Dear Afshin,

Then, the PSV needs to be sized based on fire case (vapor generation from vessel containing liquid or dry vessel whichever would be governing case).

Fallah

[Afshin445]

Dear Afshin,

Then, the PSV needs to be sized based on fire case (vapor generation from vessel containing liquid or dry vessel whichever would be governing case).

Fallah

Dear Fallah,

Do you think filter material can sustain in relief conditions (148.3 barg and 357 °C) and don't collapse before PSV opening ?

Regards
Afshin

Edited by Afshin, 08 January 2012 - 11:20 PM.

[fallah]

Dear Fallah,

Do you think filter material can sustain in relief conditions (148.3 barg and 357 °C) and don't collapse before PSV opening ?

Regards
Afshin

Dear Afshin,

Considering the filter would be full of liquid in beginning of the fire, it doesn't collapse before PSV opening.

Fallah

[Afshin445]

Dear Afshin,

Considering the filter would be full of liquid in beginning of the fire, it doesn't collapse before PSV opening.

Fallah

My understanding from all of discussion is at below:
Assumptiones:
1- Filter inlet/outlet isloation valves are closed
2- Filter is full of water
3- Initial water temp. is 25 °C
4- PSV set preesure is 148.3 barg
4- Pool fire is happend adjacent of filter

Results:
1- Water temperature start to rising and also expanding because of external
fire
2- At temperature around 48 °C, PSV start to opening due to Thermal
expansion(25% overpressre on PSV set pressure has been considered)
3- After PSV opening pressure will be decrease and water temperatre still
continue to rising
4- When the water reach to it's boiling point in PSV set pressure + 21%
overpressue (357°C), PSV open again and release steam, this will be
continue till all of filter water content discharged to atmosphere through PSV
in steam format.
5- When all of water in filter is finished then filter start to collapse due to fire

Could you please confirm if my above understanding is true.

Thanks
Afshin

Edited by Afshin, 09 January 2012 - 05:54 AM.

[fallah]

Dear Afshin,

My comments:

-At the beginning of the step 4 the relief from PSV would be two phase flow (steam and water).

-There is no information about the filter insulation and its elevation with respect to fire base. Hence the filter may be collapsed sooner than end of step 5 depend on these information.

Fallah

[ZBR]

Two thing i would add :

1- water boiling point at the said pressure is 341 C so the relieving temperature will be attained when all water has evaporated and some quantity of steam is present inside which will superheat and go to a temperature of 357 C. This would be along the path of continous temperature rising.

2- coming towards the original question, Second psv based on fire case will prevent the system from collapsing within seconds after fire is initiated, It might provide enough time for deluge valve actuation or fire fighting mechanism to actuate before collapsing, plus in caase if water is in circulation and filter is not running dry than together with this PSV filter might not fail at all. So definitely go for the second PSV.

Edited by ZBR, 09 January 2012 - 09:32 AM.

[paulhorth]

Afshin,
I agree with your description in Post no. 21, except for Step 3. The pressure will not decrease after the PSV opens, and the PSV will continue to discharge a small volume of water due to thermal expansion as the temperature rises.
I do not agree with ZBR's point no. 2. There is no need for two PSVs, just one sized for fire relief with steam flow will do the job. Furthermore, water will not continue to flow during a fire, as it is certain that the source of water, which is the water injection pipeline, will be closed by an ESDV on detection of fire.
You say the platform is normally unmanned. If a fire happens when unmanned, there is no fire protection and the filter may rupture, but this is acceptable as no-one is exposed to the risk. If a fire happens when a crew is present, the fire water system will be started, but you have no deluge. The fire crew using the monitors will be exposed to an explosion risk from this filter, so it would be better to provide a small deluge on the filter, or relocate it, to avoid this hazard. Please consult a professional fire protection engineer on this point.
I agree with Fallah's post no. 22.

Paul

[S.AHMAD]

Dear all

1. There are two emergency cases in this system namely fire cases and thermal expansion due to sun radiation.
2. The probability of occurrence for thermal expansion is most likely as compared to fire case.Meaning, overpressure due to thermal expansion by sun radiation is more frequently encountered than that of fire.
3. The volume of discharge for fire case is much more as compared to thermal radiation by sun.
4. Therefore, to avoid chattering, it is a good idea to install two PSVs. one to cater for thermal radiation (normally 3/4" size is sufficient). The other one is for fire cases, of which the probability of happening is much lower than sun thermal radiation.