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[SawsanAli311]

Dear All, 

 

I am analyzing the requirement for emergency high rate depressurization using blowdown system for hydrocarbon system. The system will surely require emergency blowdown facilities in case of fire to cater for the need to protect the vessels from BLEVE and drive the process to safe conditions by depressurizing the source causing fire escalation. 

Comparing the impacts of vessel rupture to piping system's rupture, API 521 code discusses that pipe ruptures can be more tolerable than vessel rupture specially due to the fact that vessel's failure impact area is much stronger than the case of the impact area of a pipe rupture. Also, because vessels will be more susceptible to be engulfed within fire than piping. 

Accordingly, for a system of piping manifolds partially being on grade level while the majority of the piping go to pipe rack of height above the typical fire height from the base of the pool fire (8 meters), does any foresee the requirement for emergency blowdown system or would relying on firefighting and deluge system would be considered safe for a fire scenario?

[shan]

Per API 521 (2014) Section 4.4.13.2.2 "NOTE Hydrocarbon fires can exceed 7.6 m (25 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."

 

In my opinion, if the piping section on the pipe rack is connected with the lower piping section with a BDV, you should include the volume of the piping section on the pipe rack into your BDV total blowdown load to determine the final pressure after 15 minutes blowdown. 

 

However, if the piping section on the pipe rack is an isolated piping section, it is not necessary to install a dedicated BDV just for that section because no heat input is considered above height of 7.6 m (25 ft) above the base of a pool fire.  

Edited by shan, 04 October 2018 - 03:20 PM.