Vessel Tensile strength 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

 

[ijzer]

Use API 530 Larson Miller curve for Carbon steel to calculate the estimated life time

 

[MJCronin]

Sahil...

Operating anything made of Carbon steel (especially piping) at 593C (1100F) is a bad idea.....

http://www.structint.com/what-we-do...-services/engineering-services/graphitization

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[metengr]

shin29;
With limited information you provided on the operation of the vessel and pressure, the loss in tensile/yield strength will be significant above 500 deg C, probably only 20% of the room temperature values for yield and tensile properties.

At 593 deg C time dependent properties, creep deformation, will prevail. Your primary concern should be failure from stress rupture. I can't help you with this because you provided no information on internal pressure.

 

[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

 

[metengr]

Sharad;
Ok, the additional information makes sense for a fire case scenario. If we use a similar pressure vessel steel with 70 Ksi tensile strength, the approximate minimum values at 593 deg C are as follows;

@ 593 deg C - 21 Ksi tensile, 13.3 Ksi for yield strength (values from EPRI references)

Using the Larson Miller parameter for the above material

@593 deg C, the minimum stress to cause rupture in 100 hours is ~6 Ksi
10 hours is ~9.5 Ksi

The above are approximate values but should be close enough because they represent minimum properties.

You need to calculate radial and tangential stresses in the vessel and compare with the above values.