Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
(OP)
I have a system where the predicted metal temperatures of carbon steel flare piping are lower than the MMDT of -29°C. I'm trying to figure out the allowances given in ASME B31.3 Chapter III to see if I can reduce the allowable minimum temperature.
The material is type 3 in Table 323.2.2 (carbon steel), therefore it seems that the material must be heat treated as per A333 then impact tested, however:
ASME B31.3 then goes on to say in Section 323.2.2 paragraph d that impact testing is not required provided that the stress ratio as defined in fig. 323.2.2B is <1. OK, I get that, in this case stress ratio is <1, as the MAWP is far higher than the operating pressure at the minimum temperature predicted.
Question is, does the material still have to be heat treated, even though impact testing is not required? The code doesn't specifically say whether this is the case.
ASME is a bit confusing around this point. Any help much appreciated!
Thanks!
Jim
The material is type 3 in Table 323.2.2 (carbon steel), therefore it seems that the material must be heat treated as per A333 then impact tested, however:
ASME B31.3 then goes on to say in Section 323.2.2 paragraph d that impact testing is not required provided that the stress ratio as defined in fig. 323.2.2B is <1. OK, I get that, in this case stress ratio is <1, as the MAWP is far higher than the operating pressure at the minimum temperature predicted.
Question is, does the material still have to be heat treated, even though impact testing is not required? The code doesn't specifically say whether this is the case.
ASME is a bit confusing around this point. Any help much appreciated!
Thanks!
Jim





RE: Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
However, it is possible to use a higher fidelity simulation program that may tell you what the mean metal temp is on this flare piping for this transient (?) flaring event.
RE: Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
Thanks for the reply.
I know the exact metal temperatures during depressuring, and they are below the MMDT of the metal. My question is really whether the material needs to be heat treated and impact tested, either or neither as the minimum predicted temperature is only a couple of degrees below the MMDT, and the stress ratio is only around 0.5.
Thanks
James
RE: Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
It sounds like you've got this exact metal temp from a skin temp sensor or a temp gun during an actual plant depressure run.
RE: Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
The heat treatment referred to will be specified by the particular material manufacturing standard, not necessarily A333.
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Reduction Of Minimum Metal Design Temperature As Per Asme B31.3
Dejan IVANOVIC
Process Engineer, MSChE
RE: Reduction Of Minimum Metal Design Temperature As Per Asme B31.3