Change Specification of PSV

[rojopa]

Hello,

As I am very new in world of piping, I would like to ask you questions regarding PSVs.
The inlet of PSV is 150# and outlet is 150#.
The questions:
1. Is it normal have a PSV inlet and Outlet different ratings?
2. What is rating of JIS 5K?
Your answers will be very appreciated.
Thank you very much

 

[itdepends]

1. Sometimes- but the 150# just refers to the flange rating- not necessarily the maximum pressure the PSV body can withstand- and largely unrelated to the PSV set/lift pressure. If the ratings are different then the outlet rating will be lower than the inlet rating (e.g. #300 inlet, #150 outlet).
2. No idea.

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

 

[zdas04]

Yes, it is common to have the connections on both sides of a PSV with the same ANSI Class, or the same thread rating. Why not? If something as simple as wasps build a nest in a tail pipe, a lifting PSV can easily pressurize the downstream piping to the set point of the PSV or higher. When I had that happen (the rain cap was up about 1/4 inch for reasons we were never able to determine), it suffocated all the wasps (the only good thing), blew gas out the tail pipe weep hole with a very loud whistling sound, and after about 2 minutes launched the nest 100 ft in the air. I was impressed that the nest held pressure that long. To me that example throws water on the fairly common idea that piping downstream of a PSV should be atmospheric rated since you don't have any way to trap pressure. Luckily I had put a 280 psig PSV on an ANSI 600 vessel the year before to protect a downstream component. Best we could tell the downstream component wasn't overpressured, probably due to the gas escaping through the weep hole.

I don't know what you mean by "JIS 5K" either.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[rojopa]

Thank you itdepends and zdas04 for responding my query.
Just to ammend my point indicated above:
1. What I have on my line currently inlet 300# and outlet 150#. I presume that it is normal due to high pressure at the upstream and low pressure at the downstream of the PSV.
2. I think JIS refer to Japanese Industrial Standard. What I would like to know is what is the equivalent rating of the flange JIS 5K.

Thank you

 

[SNORGY]

zdas04,

The problem might have been that the PSV was undersized. Maybe it only had a bee orifice.

 

[zdas04]

And should have had a "W"asp orifice? You could be right.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[rojopa]

Thank you for the input.

Regards

Rojopa