Rated MDMT 2

[Wasil Ali]

How is rated MDMT of a plate (30mm thick) is calculated?

Design Parameters:

Design Pressure = 5.52 MPag
Design Temperature = 176.67°C
C.A. = 3.2mm
Design MDMT = -29°C
MOC = SA-516 Gr.70N

Regards
Wasil Ali Khan

 

[david339933]

See UCS-66. First establish which curve 516-70N falls under (curve D) then look up the thickness you have in Table UCS-66 and read the temp for Curve D.

 

[GinBread]

As David said, UCS-66 has the bulk of the information you will need.

See also UG-20. If you are lucky, your customer might also allow you to use UG-20(f).

 

[david339933]

UG-20(f) is limited to 25mm thick.

 

[SJones]

Is it not -29 deg C, the same as stated in the question? If the MDMT is already set, why will it have another one?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[SnTMan]

OP, you really should state your Code of Construction. Replies given may or may not be reliable.

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[GD2]

OP could ask the question in a different way.
Is the 30 mm thick plate exempted from impact testing for required MDMT of -29 deg C?
MDMT is a design parameter, not material property.[pre][/pre]

GDD
Canada

 

[SJones]

@GD2

Spot on. There is a difference between MDMT and lowest temperature that avoids Charpy testing. Wonder what the process temperature actually is versus the nominated -29 deg C

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Chumpes]

Hello
the MDMT is the Minimum Design Metal Temperature, which definition is the minimum (cold) temperature at which a pressure equipment will be pressurized at pressure levels comparable to design pressure (we use 25% of design pressure). The MDMT is a process parameter, not a material's parameter.

I agree with SJones, UCS-66 tells you whether or not you need to perform impact test, i.e. impact tests required as per ASME BPVC when you operate below the curve for a given grade : the curve UCS 66 is minimum allowable MDMT without additionnal impact testing for a given grade.

regards

 

[Wasil Ali]

Thank you all for your support.

From the answers above and reading the ASME Code Sec. VIII Div. I 2021 UG-20(f), figure UCS-66 and UCS-66.3 Sketch e, I came to a conclusion that first we need to identify the governing thickness then go to the UCS-66 Curve and see the rated MDMT corresponds to governing thickness and Curve D

In my case two plates are making a corner joint, Plate 1 (35 mm) Plate 2 (30mm). I was confused which thickness is governing thickness which is now clear.

Thanks to all once again. really found your comments supportive.

Regards,
Wasil Ali Khan
+92 324 4392935

 

[Krausen]

Chumpes (Petroleum)12 Jul 22 14:31
Hello
the MDMT is the Minimum Design Metal Temperature, which definition is the minimum (cold) temperature at which a pressure equipment will be pressurized at pressure levels comparable to design pressure (we use 25% of design pressure). The MDMT is a process parameter, not a material's parameter.

Minor clarification: MDMT rating corresponds to the vessel's MAWP, not Design Pressure.





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