4 replies to this topic

[fallah]

Dear all,

Considering below statement included in API 521 section 5.15.1.1:


"To determine vapour generation, it is necessary to recognize only that portion of the vessel that is wetted by
its internal liquid and is equal to or less than 7,6 m (25 ft) above the source of flame.

NOTE: Hydrocarbon fires can exceed 40 m (approx. 130 ft) in height; however, experience has shown that it is
necessary only to size relief devices on the basis of the averaged heat input up to a height of 7,6 m (25 ft) above the base
of a pool fire."

As you know when bottom of vessel would be below the 7.6 m height from the source of flame,equations 6 to 12 in section 5 of API 521 can be used for relief load determination in fire case.

But if the bottom of vessel would be above the 7.6 m height from the source of flame,
1-For vessel having wetted/unwetted wall,as per above statement,what would be the basics for relief load calculations?
2-What is the height limit for considering fire effect on vessel leading to its cotainment relief?Is that limit such that the level of the vessel bottom would be below than 40 m height from source of flame(as per above API statement)?

Thanks in advance

[gvdlans]

If the bottom of the vessel is above the 7.6 m height above the source of the flame, no portion of the vessel is equal to or less than 7.6 m above the source of the flame and therefore relief device does not need to be sized for the fire case.

[fallah]

If the bottom of the vessel is above the 7.6 m height above the source of the flame, no portion of the vessel is equal to or less than 7.6 m above the source of the flame and therefore relief device does not need to be sized for the fire case.

Thanks for your prompt reply.
I personally thought same as you in this regard,but i couldn't find any fact in API 521 clearly states your above mentioned point.Would you please submit the fact (if any) included in API 521 you are reffering on for your conclusion?

[gvdlans]

I think the quotes you give in your opening post are pretty clear.

[fallah]

I think the quotes you give in your opening post are pretty clear.

Based on what to be discussed,can we say for a vessel that only fire case would be applicable and its bottom is above 7.6 m height from the fire source,there is no need to considering any PSV for its protection?