3 replies to this topic

[kc45]

Hi!

 

I have a scenario with a vessel being impinged by fire. Through the following equations, I manage to find the vessel surface temperature at each time step.

 

Eqn 1 - Heat Absorbed by Vessel due to Fire Impingement

Q = Q_R + Q_C

Q = Ɛ_Sσ(Ɛ_FT_F⁴ – T_S⁴) + H_C(T_F – T_S)

 

Eqn 2 - Temperature Rise

ΔT = [Δt(Q_R + Q_C)]/C_Sρ_SW_S

 

 

In this case, my vessel is at 85 bar and I have the depressurization curve which lasts for 15 minutes. To determine if my vessel fails, I find the point where the vessel temperature reaches 998K and that is my Time to Failure.

 

However, reading the API, they used stress and Ultimate Tensile Strength to determine the time to rupture.

Hence my approach below.

 

Vessel Stress Calculation

Since I have the depressurization curve and pressure rise due to fire impingement is small. I can calculate the following based on the internal pressure at each time step.

1. Hoop Stress

2. Axial Stress

3. Von Mises Stress

 

Vessel Allowable Stress at Elevated Temperature

As the vessel's material is a SA-516 carbon steel, I referred to the following link to obtain the allowable stress of the vessel based on the vessel surface temperature calculated in Eqn 2.

 

Link: https://www.cis-insp...e-stresses.html

 

Having these 2, the point where the line cross each other is the vessel failure time. Can I get some input if this approach is right?

 

 

 

[Pilesar]

For 1/4 inch plate steel, the metal will begin to liquefy in less than one minute with a good cutting torch. Thicker steels would take a bit longer. How is a relief valve going to protect that vessel?

[breizh]

Hi,

Consider to study the document included in the link attached.

https://www.mdpi.com...576X/4/1/11/htm

Breizh

[kc45]

For 1/4 inch plate steel, the metal will begin to liquefy in less than one minute with a good cutting torch. Thicker steels would take a bit longer. How is a relief valve going to protect that vessel?

 

Yes the calculations seem to reflect that as the equipment seems to fail within minutes when compared against the material critical temperature.
 

 

Hi,

Consider to study the document included in the link attached.

https://www.mdpi.com...576X/4/1/11/htm

Breizh

Thank you! Very informative document!