More Concerns Associated to PSV Discharge to ATM

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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. This mainly focus on PSV discharge in proper designed close collection system. In the other post "Concerns & Measures on PSV Discharge to ATM", the focus is on those PSV discharge to ATM directly. Concern on creature and rain water entering the PSV tailpipe have been discussed. Nevertheless, detail analysis on the recommendations, they are mainly tackle the issues of creatures and rain water enter. However, there are other issues such as noise, hazards, etc which subject to fluid and flow. For example, PSV discharging steam may normally high noise level. It is hot and possess hazard to operator if drain hole is provided. This post will present more recommendations for this situation.

In the other post "Concerns & Measures on PSV Discharge to ATM", the following are recommended :

1. provide screen at discharge pipe. The screen hole shall NOT too small to limit relief flow
2. vertical pipe (end section) incline 45 deg to minimize rain water ingress
3. provide eccentric type expander at discharge pipe to minimize potential rain water flush rush and particle into PSV
4. 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.
5. provide weathercap

There are two main issues needs to be managed :

1. Hazard to operator at drain hole
2. Noise at discharge pipe and drain hole
3. Erosion-Corrosion due to rain water dripping

See following image

Hazard to Operator at drain hole
PSV relief induce back pressure and partially push relieved fluid exit via the drain hole. The fluid (i.e. hot steam) could potentially discharge directly to operator.

Noise
As the fluid is relieving throught the pipe, the exit velocity will increase as the pressure is dropped to ATM. At the tip, the exit velocity may reach sonic velocity and high noise level is results. This potentially posses a hazard to operator. Similar happen to the drain hole but with much lower magnitude.

Erosion-Corrosion due to rain water dripping
Continuous rain water ingress and dripping directly on a equipment potentially cause erosion-corrosion of the equipment which potentially lead to unexpected hazard.

Knowing above issues, several measures are recommended. Further discussion in "Several Measures For PSV Tail Pipe Hazards".

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