MDMT for a fitting
MDMT for a fitting
(OP)
Hi everyone:
This is the first time I face a situation like this: I'm working in an ASME VIII-1 horizontal vessel design. Vessel has a SA-106-B Shell and a SA-234-WPB Cap on each end, plus nozzles on Shell only. Both Caps are ASME B16.9 fittings, therefore the calculation of Caps is per UG-44 rules (no thickness calculation, just the pressure-temperature ratings). Design conditions, per my customer, are the following:
Design pressure = 200 psig (no static head)
Design temperatura = 375°F
MDMT required = -25°F
Corrosion allowance = 0.125"
Outside diameter of Shell = 18"
Thickness for Shell & Caps = SCH Std = 0.375" (nominal thickness)
Shell and Caps are curve B materials
Since required MDMT is -25°F paragraph UG-20(f) is not applicable, therefore I shall follow UCS-66 rules to calculate the rated MDMT for components. I have no problem with the shell and nozzles but ¿how can I calculate rated MDMT for the Caps when per UG-44 no thickness is calculated for ASME B16.9 fittings?
¿Shall I use a procedure similar to that outlined in UCS-66(b)(1)(-b)?
I cannot find any specifics on ASME VIII-1 on rated MDMT for fittings.
Any comments/guidance will be appreciated.
This is the first time I face a situation like this: I'm working in an ASME VIII-1 horizontal vessel design. Vessel has a SA-106-B Shell and a SA-234-WPB Cap on each end, plus nozzles on Shell only. Both Caps are ASME B16.9 fittings, therefore the calculation of Caps is per UG-44 rules (no thickness calculation, just the pressure-temperature ratings). Design conditions, per my customer, are the following:
Design pressure = 200 psig (no static head)
Design temperatura = 375°F
MDMT required = -25°F
Corrosion allowance = 0.125"
Outside diameter of Shell = 18"
Thickness for Shell & Caps = SCH Std = 0.375" (nominal thickness)
Shell and Caps are curve B materials
Since required MDMT is -25°F paragraph UG-20(f) is not applicable, therefore I shall follow UCS-66 rules to calculate the rated MDMT for components. I have no problem with the shell and nozzles but ¿how can I calculate rated MDMT for the Caps when per UG-44 no thickness is calculated for ASME B16.9 fittings?
¿Shall I use a procedure similar to that outlined in UCS-66(b)(1)(-b)?
I cannot find any specifics on ASME VIII-1 on rated MDMT for fittings.
Any comments/guidance will be appreciated.





RE: MDMT for a fitting
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: MDMT for a fitting
Thanks for your reply. After reading UG-44 again and again, and per your comments I conclude that the rated MDMT for ASME B16.9 fittings shall be calculated as for straight seamless pipe but using the allowable stress of fitting material and considering the thickness tolerance for the fitting.
¿Correct?
RE: MDMT for a fitting
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: MDMT for a fitting
RE: MDMT for a fitting
RE: MDMT for a fitting
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: MDMT for a fitting
Instead of calculating the thickness of fittings,it is more easy to calculate the thickness (equivalent) as for straight seamless pipe. Please read ASME B16.9 2.1 and try to understand.
Regards
r6155
RE: MDMT for a fitting
Yes, i know that MDMT reduction is based on this but my question is, that how to calculate the "required thikness" of fitting as UG 44 states to use thickness of a straight seamless pipe?