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Sunday, December 7, 2008

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Earlier post in "Few Concerns & Recommendations of PSV Discharge Tail pipe", there are many points and requirements related to PSV discharge tail pipe have been discussed. For PSV discharging hazardous, flammable and toxic fluid shall be discharged and collected in network and disposed in good manner. For PSV discharge non-hazardous fluid i.e air, nitrogen, inert gases, steam, etc, it can be discharged to atmospheric directly.


Associate Problems
There are problems associated with direct discharge to ATM :
i) creatures (i.e. bird) build nest in the pipe potential block the discharge pipe
ii) rain water ingress results severe corrosion, seat damage, etc

Recommended Measures
Following are some recommendation to prevent above problems :
i) provide screen at discharge pipe. The screen hole shall NOT too small to limit relief flow
ii) vertical pipe (end section) incline 45 deg to minimize rain water ingress
iii) provide eccentric type discharge pipe to minimize potential rain water flush rush and particle into PSV
iv) provide a drain hole (recommend 6 mm) at low point of discharge pipe to drain any rain water ingress. ASME UG-135 andAPI RP 521 figure 1 have similar recommendation.



In the event PSV is discharging hazardous, toxic, flammable, etc fluid which potentially lead to explosive environment, thread to operator, etc, safety analysis shall be conducted to analyze the hazardous and necessary measures to avoid them. One of the recommendation is to provide vertical drain pipe instead of drain hole.

Another method may be considered is to provide a weather cap on the outlet of PSV discharge pipe. See following image.



It can avoid bird entrance and rain water ingress. The weather cap will act to release from pipe within 0.5 psi. Read more in "Yellow Jacket Weather Cap" and video clip.

Concerns
There are still some unclear concerns on this measure :
i) is local regulation and code allow ?
ii) if the discharge pipe is corroded, is the weather cap will release from pipe ?
iii) weather cap promote corrosion (crevice) underneath ?

What is your experience ?

More discussion in "More Concerns Associated to PSV Discharge to ATM".

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posted by Webworm, 12:51 PM

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