22 replies to this topic

[shin29]

Dear all, I am stuck to size a PSV where Design pressure of the vassel is 100 barg but the Operating pressure of the same vessel is 20 bar G . There are chances of pressure rise to 100 barg as upstream of vessel deal with such high pressue . Let's See fire case Now as per formula mention in API 521 Reliving Capacity is propotional to (T (wall) - T (reiliving)) So if Twall is considered to 593 degC . Wall Temperature - 593 deg C Reliving Pressure (Fire Case ) - 120 barg Operating Pressure - 20 barg Operating Temperature - 30 deg C Reliving Temperature - 1472 Deg C Now Now as per formula mention in API 521 Reliving Capacity is propotional to (T (wall) - T (reiliving)) . which is negative Besides it is desirable that the gas temperature should not be more than wall temperature as at such high temperature Vessel shall rupture befor it reach the PSV set Pressure. I need you to help me on this Regards, Sahil

[fallah]

Sahil,

 

Appears you are describing the gas expansion case in a vessel due to engufing in a pool fire.  

 

Anyway, in such cases that the DeltaT would be negative you can take it as minimuim positive value as possible; normally 0.01

[shin29]

Dear Fallah, 

 

Thanks for resposne ,

You are right, I am talking about a vessel filled with Methane at Operating condition and then expansion of gas due to fire outside.

on of my concern is that the temperature of the gas reaches more than 593 Deg C at quite low Pressure than the set Pressure . The wall temperature shall be heated more , their rupture stregnth shall decrease and the vessel may rupture well below its set Pressure .  

Does it COunts or it it count than how to deal with it .

 

other thing in my mind is if the source of heat to gas is wall temperature , can it be in any case more than the wall Temperature .

 

Regards,

 

Sahil

[fallah]

 Sahil,

 

My comments in red color are as follows:

 

 The wall temperature shall be heated more , their rupture stregnth shall decrease and the vessel may rupture well below its set Pressure .  

Does it COunts or it it count than how to deal with it .

 In fact, in most fire cases the PSV cannot protect the vessel against failure and the vessel would fail before PSV opening. Then one just can deal with this matter that the vessel would fail even in PSV presence which mostly has been installed for code satisfaction...

other thing in my mind is if the source of heat to gas is wall temperature , can it be in any case more than the wall Temperature .

 Yes, the gas temperature cannot become more than vessel wall temperature as long as the wall wouldn't be failed. For this reason the Delta T cannot be negative and, as mentioned, in the cases the calculation show a negative value the minimum positive value (0.01) should be taken...

 

[S.AHMAD]

My understanding for gas expansion due to fire is not to protect the vessel but to prolong the time taken for the fracture to occur. so that emergency team have some time to shut off the source of fire. If fire continues, fracture will occur due to weakening of the vessel material of construction not due to gas expansion.

[fallah]

 If fire continues, fracture will occur due to weakening of the vessel material of construction not due to gas expansion.

 

AHMAD,

 

But weakening of the vessel material itself would be promoted by the build up pressure inside the vessel due to gas expansion...

[paulhorth]

Sahil,

As Fallah has explained, the PSV will not protect this vessel from rupture in a fire.

To protect this vessel you should consider providing the following:

(1) a blowdown system to reduce the pressure and inventory

(2) a water deluge system to keep the shell cool

(3) passive fire protection (which will prolong the exposure time till rupture)

(4) adequate drainage below the vessel to reduce or eliminate the risk of a pool fire. However the risk of a jet fire impinging on the vessel, from outside or from part of the vessel itself such as an instrument flange, remains.

 

Paul

[shin29]

Dear All, 

i take this discussion as opportunity to strethen my basics .

My understanding is once the fire is around the vassle , the wall Temperature starts increasing . as it reach 593 deg C (as per API 521 Figure 1 and 2 : it will take 11 min for .7 inch thick ss plate to reach this Temperature ) , the gas insside reach the same temperature with pressure 70-75 barg ( considerig operating Temp- 30 deg C and Pressure 30 barg).

 

As the temperature of wall increses so does the temperature and pressure of the Gas inside. Now most probably the vessel will ruture due to high temperature and pressure before the PSV could pop.

 

Such cases should not be rare during designing . what precaution wwe should take to counter this .

I mean installing PSV just for statuatory requirement and not fullfilling its purpose would be absurd ..

YOU people must have encountered such scenario before ..

 

Regards,

 

Sahil 

[shin29]

Sahil,

 

Appears you are describing the gas expansion case in a vessel due to engufing in a pool fire.  

 

Anyway, in such cases that the DeltaT would be negative you can take it as minimuim positive value as possible; normally 0.01

IF i put delta T = .01 , the relieving Capacity  (as pe API 521  equaton 8); becomes very low . Kindly clarify what to do

[fallah]

 IF i put delta T = .01 , the relieving Capacity  (as pe API 521  equaton 8); becomes very low . Kindly clarify what to do

 

 

Sahil,

 

If you are using API 521 Fifth Ed.. the equation is No. 12.

 

Anyway, it doesn't matter and you can go ahead. It shows the vessel will fail before PSV opening and you need a small PSV mostly for code satisfaction.

[paulhorth]

Sahil,

 

 

what precaution wwe should take to counter this .

I have already given you an answer to this question.

I repeat:

To protect this vessel you should consider providing the following:

(1) a blowdown system to reduce the pressure and inventory

(2) a water deluge system to keep the shell cool

(3) passive fire protection (which will prolong the exposure time till rupture)

(4) adequate drainage below the vessel to reduce or eliminate the risk of a pool fire. However the risk of a jet fire impinging on the vessel, from outside or from part of the vessel itself such as an instrument flange, remains.

 

It is the responsibility of you and your colleagues in the other disciplines to assess the risk of a fire, and determine if these precautions will reduce the risk of death resulting from vessel rupture to below an acceptable limit, which is usually defined by the operating company's safety philosophy.

 

Paul

Edited by paulhorth, 21 December 2013 - 04:04 AM.

[shin29]

 

 IF i put delta T = .01 , the relieving Capacity  (as pe API 521  equaton 8); becomes very low . Kindly clarify what to do

 

 

Sahil,

 

If you are using API 521 Fifth Ed.. the equation is No. 12.

 

Anyway, it doesn't matter and you can go ahead. It shows the vessel will fail before PSV opening and you need a small PSV mostly for code satisfaction.

 

Dear Fallah ,

With all respect i don't understand that While preparing data sheet for the client , how does it look to produce a data sheet of PSV with that much small quantity .

I have never seen such a data sheet . I don't know if this factor is practiced in Industry.

Kindly clarify 

[fallah]

With all respect i don't understand that While preparing data sheet for the client , how does it look to produce a data sheet of PSV with that much small quantity .

I have never seen such a data sheet . I don't know if this factor is practiced in Industry.

Kindly clarify 

 

 

Sahil,

 

Small quantity of PSV relieving capacity is the output of your design calaculations!...and as mentioned it would be a small PSV just for code satisfaction...

 

Indeed, the relieving capacity is one data among many ones should be reflected on a PSV data sheet and doesn't matter is high or very low. There would be other important info such as material, pressure rating, governing code, relieving fluid properties, should be reflected on the data sheet by which the vendor can select the proper one matching your system...

 

If it still isn't so clear, please be specific on the point you need to be more satisfied...

Edited by fallah, 24 December 2013 - 02:09 AM.

[Sharma Varun]

 

 

 IF i put delta T = .01 , the relieving Capacity  (as pe API 521  equaton 8); becomes very low . Kindly clarify what to do

 

 

Sahil,

 

If you are using API 521 Fifth Ed.. the equation is No. 12.

 

Anyway, it doesn't matter and you can go ahead. It shows the vessel will fail before PSV opening and you need a small PSV mostly for code satisfaction.

 

Dear Fallah ,

With all respect i don't understand that While preparing data sheet for the client , how does it look to produce a data sheet of PSV with that much small quantity .

I have never seen such a data sheet . I don't know if this factor is practiced in Industry.

Kindly clarify 

 

Shin this is one of the strange ways engineering world behaves some times, during detail engineering for a major operator in UAE I found a PSV PDS in FEED specifying 0 kg/hr flowrate, they had provided a 2" nozzle for it. It was found that it is typical case of gas expansion and vessel wall fails before fire case relieving conditons, a safety fellow & PMC commented that we will not accept the vessel without a PSV, and suggested to put a dummy PSV with smallest possible size. However the project philosophy was based on SHELL DEPs & finally we got the PSV deleted under special considerations.

paulhorth has very efficiently given you the answers you are seeking-

"To protect this vessel you should consider providing the following:

(1) a blowdown system to reduce the pressure and inventory

(2) a water deluge system to keep the shell cool

(3) passive fire protection (which will prolong the exposure time till rupture)

(4) adequate drainage below the vessel to reduce or eliminate the risk of a pool fire. However the risk of a jet fire impinging on the vessel, from outside or from part of the vessel itself such as an instrument flange, remains. "

[Sushant Labhasetwar]

ASME Section VIII, Div,1, UG-140 can be followed for such case. UG-140 allows not to have a relief valve provided detailed documentation is provided and detailed requirements mentioned therein are followed.

[Propacket]

shin29,

 

Is gas expansion the only credible scenario for your vessel? I have come across such situation where vessel will fail before PSV pops but by working with our client, we rejected this scenario as being not credible and considered other credible scenarios. 

[shin29]

Dear All, 

My query is regarding a Vessel made of API 5L Gr. X70, 

Wall Thickness is  24 mm

Outer Dia meter is : 40 inch.

 

During sizing of PSV for this system i found out that the wall temperature is increasing beyond 593 Deg C before the PSV set point .

 

My doubt is how to relate the Vessel tensile stregnth with the incresed wall temperature. So as to find out at what condition ( Pr and T combination )  the vessel may  get ruptured before the PSV pops up.

 

Thanks ,

 

Sahil

[fallah]

 

My query is regarding a Vessel made of API 5L Gr. X70, 

Wall Thickness is  24 mm

Outer Dia meter is : 40 inch.

 

During sizing of PSV for this system i found out that the wall temperature is increasing beyond 593 Deg C before the PSV set point .

 

My doubt is how to relate the Vessel tensile stregnth with the incresed wall temperature. So as to find out at what condition ( Pr and T combination )  the vessel may  get ruptured before the PSV pops up.

 

 

Sahil,

 

As far as i know, you might first estimate the burst pressure, let say by Barlow's equation, using relevant ultimate tensile strength. Then find the temperature corresponding to this pressure..

[shin29]

Dear Fallah,

 

Doesn't Ultimate tensile stregnth very with temperature . My under standing is With incresing temperature Ultimate tensile stregnth shell weaken and therefore the burst pressure shall also be lower as per burlow' temp . That is why i think i should know the Ultimate tensile strength at veriying temperature and then  i can calulate the burst pressure with burlow's formula . kindly correct me if i am wrong.

 

Besides as you mentioned ,  i come up with burst pressure of 312 bar ( UTM 70300 psi, th : 23 mm, OD : 28 " ) . now how should i go ahead to find the temperature and so.. 

 

Thanking you for your responses 

Your sincerely 

sahil 

[fallah]

Sahil,

 

Please find below my comments in red color:

 

 

Doesn't Ultimate tensile stregnth very with temperature . My under standing is With incresing temperature Ultimate tensile stregnth shell weaken and therefore the burst pressure shall also be lower as per burlow' temp . That is why i think i should know the Ultimate tensile strength at veriying temperature and then  i can calulate the burst pressure with burlow's formula . kindly correct me if i am wrong.

I think you are right...but you should try with trial and error. You can estimate a temperature by which you can caculate the relevant burst pressure. Then you should obtain the temperature corresponding to this burst pressure in equilibrium standpoint. If this temperature would be around that estimated temperature, your estimation is correct otherwise you should estimate another value for temperature and repeat the procedure till finding the right temperature value...

Besides as you mentioned ,  i come up with burst pressure of 312 bar ( UTM 70300 psi, th : 23 mm, OD : 28 " ) . now how should i go ahead to find the temperature and so.. 

I think my answer for the first item would be applicable for this item too...

 

 

[shin29]

 

Sahil,

 

Please find below my comments in red color:

 

 

Doesn't Ultimate tensile stregnth very with temperature . My under standing is With incresing temperature Ultimate tensile stregnth shell weaken and therefore the burst pressure shall also be lower as per burlow' temp . That is why i think i should know the Ultimate tensile strength at veriying temperature and then  i can calulate the burst pressure with burlow's formula . kindly correct me if i am wrong.

I think you are right...but you should try with trial and error. You can estimate a temperature by which you can caculate the relevant burst pressure. Then you should obtain the temperature corresponding to this burst pressure in equilibrium standpoint. If this temperature would be around that estimated temperature, your estimation is correct otherwise you should estimate another value for temperature and repeat the procedure till finding the right temperature value...

Besides as you mentioned ,  i come up with burst pressure of 312 bar ( UTM 70300 psi, th : 23 mm, OD : 28 " ) . now how should i go ahead to find the temperature and so.. 

I think my answer for the first item would be applicable for this item too...

 

Dear Fallah, 

Can you please help me to calculate burst pressure of estimated Temperature . 

I need to know Ultimate tensile strength for the Material on this temperature and than from burlow's formula I can find out the Burst Pressure .  But I am not able to find out some relation or table to find out UTS at estimated temperature for the perticular material  .

Please correct me if there is some other way to find out burst pressure at estimated temp. 

 

Thanks and Regards,

Sahil

 

[fallah]

Sahil,

 

You can use the graphs a sample of which is attahed.

Attached Files

•  UTS vs Temp.docx   167.42KB   14 downloads

[shin29]

Thanks alot fallah for your kind cooperation