UG-20 MDMT 4

[AJerry]

In ASME Section VIII Div 1 UG-20 MDMT includes the lowest operating temperature e.g. atmospheric except as permitted in (f) (3): states the Occasional operating temperatures colder than -20 deg F. are acceptable when due to lower seasonal atmospheric temperature.
Could someone explain what is Occasional means, if in the winter the temperature is -30 deg. F for 3 weeks is this still considered Occasional?

 

[CodeRef]

No, it is Seasonal in my opinion. Sometimes a temperature drop could be longer or shorter than three weeks depending on the season.

Also see UCS-160 (a) and (b) There is an example given in Appendix L paragraph L-9.6.3 where an occasional temperature drop to -10Deg F affects the thickness based on a "pressure loading" case only. ie...the Press/Temp/Vol relationship.

In my opinion,
Occasional is short periods of time and not Seasonal. Use your best judgement and common sense and be able to defend it. If you are not willing to defend it, then design for the lower temperature.

The real question is, what would Al Gore say?


There are three kinds of people in this world; those who can Google and those who can't.

 

[doct9960]

AJerry,

If you look up a dictionary, "occasional" means an infrequent or rare occurence. The "occasional" in UG-20(f)(3) pertains to the operating temperature, not the seasonal atmospheric temperature. So what would be the resulting operating temperature due to that three weeks of -30 deg F atmospheric temp.?

The 2nd sentence in UG-20(f)(3) applies more to the Operations people. Vessel designers and fabricators are mainly concerned on the 1st sentence. If you are operating a vessel that was designed by the rules of UG-20(f) and your vessel's operating temperature goes below -20 deg F as a result of that three weeks of cold weather, then you need to make some process adjustments to bring up that operating temperature to where it should be in the shortest possible time.

My opinion only.

 

[eliebl]

What about the piping which attaches to the vessel? B31.3 does not have a similar provision for seasonal temperatures occasionally below the minimum temperature.

I'm sure a few people would ask questions of the vessel is designed to -20 F when the piping is designed to -50F.

EJL

 

[SnTMan]

As I recall, at an HSB seminar some years back, the UG-20(f) exemption was said to be in place for the manufacturers of air receivers, mostly the smaller home models.

Regards,

Mike

 

[doct9960]

ABSA (pressure equipment authority in Alberta, Canada) had a presentation back in 1999 about impact testing.

http://www.absa.ca/Forms/AB-511 Impact Testing Enigma.pdf

See Section 4.5 Exemption Combinations on the above presentation. ABSA does not recommend temperature reductions (i.e. UCS-66(b), UCS-68(c)) in addition to the UG-20(f) exemption.