MDMT PV Elite 4

[shady2554]

Hi guys, please what can i do to reduce the MDMT of a pressure vessel. I have this warning at the end of the design [highlight #FCE94F]"Warning: Computed overall MDMT was higher than the required value !".[/highlight]
Although ok with client spec but i there anything i can do to influence the value

 

[brkmech1234]

Why do you want to infuluence the value? Assumung that you gave given the proper input, if the above stated message appears, you need to provide impact testing.

If you need help furthur, you need to provide the furthur details so that others can understand the problem better.

 

[vesselfab]

Apparently, your design is not adequate for the required MDMT. There are several things you can do.
I am assumining it is a carbon steel vessel and you don't give the materials you selected.
You can add normalization to the materials.
You can add PWHT.
If the problem is self reinforced nozzles you can go to SA-350-LF2
if all else fails you can add CLVN to the materials and do production impact testing.

Without your requirements or you materials selected, not much else cand be said.

 

[shady2554]

ok, for clarity, i am designing an MP Separator, design condition is 33barg pressure, @100 deg C with vessel diameter 2.4m, T/T length is 7.3m.
The MDMT is showing a warning for the computed. the selected is -20 deg C, the computed is 35 deg C.
the warning is as highlighted above, that the computed is higher than required. So i don't know what to do.

 

[SNORGY]

Here would be my initial guess.

At 33 bar (3401 kPag) and 8 ft diameter, with 1/16" C.A., I computed a vessel shell thickness of 1.5"; if you are getting a computed 35 C MDMT then you probably have specified a Curve A material (ASME Section VIII Division 1 Figure UCS-66 / Table UCS-66). You can almost get to the MDMT you want by specifying a Curve D material such as SA-516-70 N.

 

[jtseng123]

vesselfab, I am pretty rusty in code. Where in the code stating PWHT related to MDMT ?

 

[gr2vessels]

shady2554,
The problem appears to be in the material selection window, make sure to select the correct heat treatment (normalized or not) and the correct impact test curve.
Cheers,
gr2vessels

 

[shady2554]

Thanks guys you've all been of great help. I checked the curve and normalised it reduced the MDMT from 35 to 30deg F, and the warning is still there.

 

[SNORGY]

shady2554,

What are the computed shell / head / nozzle neck thicknesses and materials? Some component or other is limiting.

Are you sure the material that the program is working with is Curve D? I somehow doubt it. Are things 4.5 inches thick?

If a piping component is limiting, see also ASME B31.3 323.

 

[jamesl]

jtseng123,

Refer to UCS-68(c) for PWHT and impact test exemption temperature reduction.