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Rated MDMT

Rated MDMT

Rated MDMT

Under what circumstances SA105 Flanges (B16.5) will have a rated MDMT of -155DegF? What went wrong?

RE: Rated MDMT

See UCS-66(b)(3).

  Tom Barsh
  Codeware Technical Support

RE: Rated MDMT

Thanks for the reply.  Pls explain in more details, thanks.

RE: Rated MDMT

I have similar confusion!

For my nozzle assembly(Flange:SA-105,Neck:SA-106-B,Pad:SA-516-70).

Design MDMT is 30F. In the process of reducing MDMT,I calculate Level 1 MAT(Minimum allowable temp) to be 10.38 F for this nozzle assembly considering UCS-66 Impact test excemption curve.And when further reducing this MAT for Neck using curve UCS-66.1, I found out my Coincident ratios(Rts) are too small.Please see following table:

Pressure      P psig   S*E*  (Rts=S*E*/SE) Tr?F     MATR

MAWP            175    17100       1.00          0           0
Design            155      569       0.03       52839     -52839
40% MAWP     62      227       0.01      423675     -423675
Start Up       111      407       0.02      113850     -113850
Operating       123      451       0.03      90037     -90037

Now I am confused while making the decision regarding my finallly reduced MDMT.I Checked API579 chapter 3(2007 edition),On page 3-9 under STEP 4 i)1)it states that if the Rts value is less than or equal to the thresold value on UCS 66.1(which in my case is 0.3) set the MAT to -150F.

So Should I Consider the same MAT(-150F) for Nozzle flange and Pad material and set the MAT(Ultimately Final MDMT) for Nozzle assembly to be -150F or Sould I consider UCS-66(b)(1)(b) and restrict the MAT(Final redused MDMT) of the flange to -55F and hence the MAT(Final reduced MDMT) of the whole nozzle assembly to -55F?!

I really really need some ones help to clarify this confusion.

Best regards

RE: Rated MDMT

How ASME determine -55F or why API determine -150F are beyond me.  But, one thing for sure is, your Design MDMT is 30F, with MAT of -55F or -150F, ASME or API, you are save.

Sorry that does not answer your question and so was TomBarsh did not answer my question!

RE: Rated MDMT

well when I mentioed my design MDMT is 30F.That number is give on the Fabrication drawing. Now our client has give us the new information & i am trying to evaluate if this vessel will be okay for New MDMT of -37F?


RE: Rated MDMT

According to ASME (-55F) and API (-150F), if you have calculated correctly, you are OK with -37F.

For low pressure applications (say less than 100PSI) UCS66 curves scared a lot of people using carbon steel pressure tank fabrications and with the calculation of Rts, UCS-66(b)(1)(b) almost telling you can use any low grade carbon steels.

RE: Rated MDMT

Good Afternoon SamCheung,

I am sorry that you feel that I did not answer your question.

However, you asked "Under what circumstances SA105 Flanges (B16.5) will have a rated MDMT of -155DegF?"

I directed you to ASME Code Section VIII Division 1, paragraph UCS-66(b)(3). This paragraph applies to standard B16.5 flanges as well as to other components.

  Tom Barsh
  Codeware Technical Support

RE: Rated MDMT

Pls elaborate why -155F and what is so special about this -155F, thanks.

RE: Rated MDMT


Does UCS-66(b)(3) means: When the intended MDMT(not design MDMT)is between -55F to -155F and coincident ratio is less than or equal to the 0.35(lower thresold limit on UCS 66.1)than the componet under evaluation can assume the value of MAT(or rated MDMT) to be -155F.

Do you think my interpretation is correct?!


RE: Rated MDMT


Is not it correct that the SA-105 material's MDMT is restricted to -55F(accordig to UCS-66(b)(1)(b)) without performing the impect testing.

Is n't it correct when the Intended MDMT(worst condition during operation) is lower than design MDMT especially below -55F than impect testing of materail(including SA-105) is required. Or use different material such as SA-350-LF3 for flange?


RE: Rated MDMT


I don't think the question you are asking is specifically Compress related. Tom has tried to help, but if you need more, I'd suggest posting your generic ASME Code issues in the ASME Code forum. forum292: ASME (mechanical) Code Issues


RE: Rated MDMT

Sorry about it! Will take care next time!


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