Pipeline vessel Tensile stress vs Temperature

[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 if the vessel gets ruptured before the PSV pops up.

Thanks ,

Sahil

 

[JStephen]

The ASME code specifies allowable stress at different temperatures and would allow a vessel designer to specify maximum pressure at varying temperatures. I assume other vessel codes are similar. It doesn't necessarily specify a rupture pressure at each temperature.

 

[weldstan]

What design allowable stress did you use? If the temperature reached 593C during operation, whatever design stress was used was inadequate and the material no longer will provide the 70 ksi SMYS.. API 5LX-70 is not permitted by ASME VIII.

 

[LittleInch]

The fact your title says pipeline vessel and it's built of x70 tells me you've got a short pipe you're using aa pressure vessel.

What design code is it designed to?

This should give you your de rating factors, but it sounds like a fire case?

A few more details please.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[shin29]

Dear All,
I am sorry for the limited information that i provided .

Further , I am sizing a PSV for the Vessel in fire case.
Set point : 100 barg ( The vessel is required to be Design for MAWP of 100 barg)
Op Temp : 20 Deg C
Op Pressure : 30 bar

Now relieving Temperature of the vessel comes as 858 Deg C . Which is quite high than the default wall temperature as per API 521 i.e. 593 Deg C .

My point is , in case of fire, the vessel shall keep on heating up, the inside pressure builts up . At some time the wall temp as well as the inside gas temp shall cross 593 Deg C . But the PSV shall not pop unless the Temp is 858 DEg C ( at that Temp Pressure shall be the set point of PSV)

I want to check if vessel may rupture way before the PSV pop up . Because of weakening of the material due to increase Temp.
That's why i want Tensile stregnth of the vessel vs Temp..

Hope I clarified . and somebody could help me.
Regards,
Sharad

 

[LittleInch]

I've seen this discussed many times in the "safety relief valve forum" . I can't remember what the solution is, but it's not uncommon for a gas or part gas filled vessel. Search in that forum and you'll find many similar questions.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[MJCronin]

WOW...

858C (~1570F) !.... You are in the operating range of superheater tubing in a fossil fired boiler. ! !

Most steels have little or no strength in this range...

I do not believe that your vessel will be under pressure when it reachs these temperatures in a fire.....

What about the contents of this vessel ?

Have you considered that the contents have vaporized, and significantly increased pressure (thereby actuating the relief valve) a long time before the vessel wall reaches 858C ????

I believe that there was an article in Chemical Engineering Magazine (by Wong ??) some years back discussing this type of analysis...

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[LittleInch]

Shin29,

what you have shown is that at the design pressure you have the vessel will not need a pressure relief because the vessel will have failed well before then.

What you then need to do is work out whether this vessel failing will add to the inferno in a significant way or release poisonous chemicals. If it does you need to find a way to prevent it getting this hot in a fire (bury it, cover it in concrete, deluge it in water etc ) or lower your design pressure so that the PSV does lift n a fire before the vessel melts and ruptures

Past the max design temp of the vessel material it doesn't apply any more and you need to assume failure of your pipe / vessel.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[LittleInch]

see

http://www.eng-tips.com/viewthread.cfm?qid=328695

and

http://www.eng-tips.com/viewthread.cfm?qid=215738

or this one -

http://www.eng-tips.com/viewthread.cfm?qid=357254

read down a bit and you'll see that a PSV may not be required if fire is your only relieving case

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way