3 replies to this topic

[achilles09]

Am new to this forum...Benefited lot from the expert opinions given here....

I need a clarification....

Many companies have the design practice of fixing the vessel design pressure 3.5 kg/cm2 g as minimum in case discharging to flare . Whether there is any particular reason for fixing. I don't think so ASME sec VIII imposes any criteria like this.

Kindly clarify.

Thanks and regards,

Achilles

[Art Montemayor]

Achilles:

The main reason for setting a "minimum" pressure is not due to favoring heavy-walled vessels. Rather, it is to ensure that the vessel is properly designed (pressure-wise) in order to contain gases with enough driving force (pressure) to reach the flare burner's specified inlet pressure. You usually have two types of flares: low pressure and high pressure. Low pressure flares are usually around 30 to 50 psig in their relief headers; 3.5 kg/cm2 is within that range.

[ankur2061]

Am new to this forum...Benefited lot from the expert opinions given here....

I need a clarification....

Many companies have the design practice of fixing the vessel design pressure 3.5 kg/cm2 g as minimum in case discharging to flare . Whether there is any particular reason for fixing. I don't think so ASME sec VIII imposes any criteria like this.

Kindly clarify.

Thanks and regards,

Achilles

Achilles,

Flare knockout vessels & seal vessels are designed according to the guidelines given in API STD 521. Here is what Section 7.3.2.4 of API STD 521 has to say regarding design pressures of flare knockout & seal vessels:

Most knockout drums & seal drums are operating at relatively low pressures. To ensure sound construction, a minimum design gauge pressure of 345 kPa (50 psi) is suggested for knockout drums in subsonic flare or other low-presure applications. A vessel with a design gauge pressure of 345 kPa (50 psi) should not rupture if a deflagration occurs. Stoichiometric hydrocarbon-air mixtures can produce peak exlosion pressures on the order of seven to eight times the absolute operating pressure. Most subsonic-flare seal drums operate in the range of gauge pressure from 0 kPa to 34 kPa (0 psi to 5 psi)

Hope this helps.

Regards,
Ankur

[achilles09]

Thanks ART , ANKUR.

This helps me lot