4 replies to this topic

[eastorca]

Hello all,

As per API 521 2007, section 5.20.1, it recommends that reducing the equipment pressure from initial conditions to a level equivalent to 50% of the vessels design pressure within approximately 15 min. This criterion is based on thickness of approximately 1 in or more. Vessel with thinner walls generally require a somewhat faster depressurizing rate. The required depressurizing rate depends on the metallurgy of the vessel, the thickness and initial temperature of the vessel wall and the rate of heat input. API also figures out an example for Grade 70, but it quite confuses me to determine maximum allowable required depressurizing time.

My question is that how to ensure the selected depressurizing time is suitable. This is to ensure vessel shall not be rupture before completion of depressurizing.

- How to determine the temperature of vessel causing by fire to be referred for benchmark at Figure 2 - page 39. (API classify 1000, 1200, 1300, 1400)?
- How to determine the rupture stress of vessel material (note Grade 70)

Thanks

[fallah]

My question is that how to ensure the selected depressurizing time is suitable. This is to ensure vessel shall not be rupture before completion of depressurizing.

eastorka,

Normally, for each 5 mm decrease in thickness (from 25 mm) 3 minutes is subtracted from 15 minutes and this time would be applied as depressurizing time for thinner wall vessel.

Fallah

[aju_1807]

Fallah,

Interesting basis but where it came from or is it rule ofthumb?

[fallah]

Aj,

It is from engineering practice which we are using in our "gas refinery" projects.

Fallah

[aju_1807]

Thanks and if you dont mind can you share that with us?

rgds,

Aj