8 replies to this topic

[mahmooddalvi09]

Hii all,

 

To calculate Environmental factor "F"  in pool fire-wetted case relief load calculation, API - 521 has an equation as mentioned in attached picture.

 

My query is 

 

1. K is the thermal conductivity of insulation at "mean temperature" (W/m.k). What mean temperature should be taken? Is it mean of design and relieving temperature or MOT and relieving temperature?

 

2. As thermal conductivity of insulation increases with temperature, is it ok if i consider thermal conductivity at relieving temperature instead of mean which would result in higher value of F and thus heat load "Q"?

 

Please suggest.

Attached Files

•  F factor equation.png   33.35KB   9 downloads

[Pilesar]

During heat transfer, insulation has a hot side and a cold side. The heat transfers from the hot side to the cold side. The insulation acts as a resistance to the heat transfer. The mean insulation temperature would be the average temperature of the insulation where the heat transfer is being considered. In a pool fire, the temperature of the insulation is a function of the temperature of the hot air on the outside of the insulation and time. During a pool fire, the insulation temperature will be higher than the pressure vessel wall temperature which will be higher than the temperature of the vessel contents. The insulation resistance affects the rate at which the heat is transferred to the outside of the vessel wall..

[mahmooddalvi09]

That's great explanation Pilesar.

Still in practical situation how would I know the "mean temperature" of insulation as neither do I have temperature of hot air(due to fire flames) on the outside of insulation nor the vessel wall temperature?

[latexman]

how would I know the "mean temperature" of insulation as neither do I have temperature of hot air(due to fire flames) on the outside of insulation nor the vessel wall temperature?

How about the adiabatic flame temperature of the spilled liquid on the outside of the insulation and the coincident temperature of the relieving fluid at 1.21 X MAWP on the inside of the exhaust pipe/insulation?

That should be close enough.

[mahmooddalvi09]

Got it. Thanks!

[shvet1]

Mahmood, do you consider regular thermal insulation of specific fireproof insulation?

 

Still in practical situation how would I know the "mean temperature" of insulation as neither do I have temperature of hot air(due to fire flames) on the outside of insulation nor the vessel wall temperature?

Conservative approach is @1660°F

Edited by shvet1, 19 August 2024 - 12:17 AM.

[mahmooddalvi09]

Dear Shvet1, Thanks for the reply!

 

I am considering F=1 for the conservative approach.

 

Given case is for fireproofing insulation. As what i know we don't take credit for regular thermal insulation. am i right?

[shvet1]

Correct. Regular insulation has some fireproof capabilities but wiring/fasteners by which that is fixed to a vessel are not. So regular insulation usually is pulled away by flame.

[mahmooddalvi09]

Okay, Thanks!