[ ASME Flange rating ] 3

[gguliye]

Dear PSV team,
the customer requires a spring valve from me with LCC body 150 # inlet outlet, flange and SS trim
parameters are as following:
set pressure 16 barg
Operating/relieving temperature: 107.6 F
-50.8/392 F is the design min and max
the program says the following: the inlet pressure should be less than app 14 barg in the given temperature for 150 # flange rating. I have checked with ASME and program is right. However, the customer is asking how it has been given originally? Where can be such a case that we ignore the pressure temperature limit?
The sizing is thermal relief case

 

[RVAmeche]

It sounds like you're saying > 14 barg is greater than the pressure/temperature limit for the flange based on the ASME tables. It's simple, they need 1) a different set pressure, 2) a different material

I'm not sure what you mean when you say "how it has been given originally"... I assume you're asking how did they obtain a relief valve previously? If that's what you mean, someone (client/engineer who spec'd it, or maybe the manufacturer (less likely)) didn't mention the -50F minimum temperature. The valve was never suitable for that service.

Also, are you sure the minimum/maximum temperatures are -50/392F? Unless you're running a steam line in a very cold climate, that's kind of an unusual temperature swing for a process.

Finally, you say sizing is thermal relief. I know nothing about your process but given the temperature range alone, I'm doubtful that's actually the governing case. Consider re-analyzing the potential scenarios and see if there are other, more significant cases to consider (such as pressure regulator/control failure, abnormal heat input, etc). If the client has said "it's just thermal relief" I'd take that with a giant grain of salt if they previously had a valve not fit for that service.

 

[gguliye]

Sir,
Thank you very much for Ur answer.
Just checked. not -50 but 394 F has been creating a problem.
regards,

 

[The Obturator]

I noted your last comment re the higher temperature.
For SRV flange rating selection the set pressure and relieving temperature is primarily used. The flange also needs to be suitable for normal operating conditions.

You have also stated DESIGN minimum and maximum temperatures, Here the material (body) needs to be suitable for that range hence "LCC" has been used. Generally in the SRV world, design temperatures are used for the material selection rather than the flange rating. For the flange rating, consider the operating and relieving temperature (except in external fire cases).

What you have not addressed/mentioned is the normal operating pressure.

Depending on the sizing/selection program used, it may be using the temperature and pressure extremes to determine the 14 bar limitation result.


Per ISO, only the term Safety Valve is used regardless of application or design.

 

[gguliye]

Valve man,
I understand that it is thermal relief and it is highly surprising that the temperature will rise to 200 degrees Celsius ( due to sun ). May be it is the design temperature of the equipment which the valve will be used for and higher than the Temperature which can be achieved through thermal relief. That's how I imagine it
Thx for Ur help