How to determine MDMT for the flanges of Appendix 2

[mechengineer]

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Hi expeprts,
For B16.5/B16.47 flanges (CS), as per UCS-66 (c), MDMT is -18 deg.C for forged condition and MDMT is -29 deg.C for fine grain practice and normalized. The questtion is that, is UCS-66 (c) applicable for the flanges design by Appendix 2? If not, using B16.47 flange or Appedix 2 flange may have the different MDMT. Code does not give how to determine the MDMT for the flange except UCS-66 (c). Here is not talking about the weld joint, but the MDMT for individulal pressue component of the flange.

Whatever what the B16.5 flange class (150, 300, 600, 900, 1500, 2500) is and what g0 is, UCS-66 (c) gives that the MDMT is -18 deg.C for forged condition and MDMT is -29 deg.C for fine grain practice an normalized that seems diffical to understand what the basis is for UCS-66 (c).

I think that the MDMT of flange may be the minimum MDMT of UCS-66 (c) and the calculated as per the governing thickness (g0) of the flange whatever B16.5 flange and Appendxi 2 flange.

UCS-66 for MDMT is only subject to the general primary membrane tensile stress, not the local combined stress or the bending strese in the flange.

Thanks.

 

[Geoff13]

Are you able to look at the 2010 edition (or earlier) of Section VIII Div 1? Does the example in L-9 give you any help? It discusses applying UCS-66 and includes an Appendix 2 flange.

Appendix L changed after 2010, so the example no longer exists.

 

[mechengineer]

@Geoff13, I go through the excample in L-9 of VIII Div 1, 2010, but it doesn't help to have the answer on my question.
The attached is an example of MDMT I did for 24" flange. The MDMT has a big difference by using UCS-66 (c) and Figure UCS-66M Impact Test Exemption Curves with the governing thickness g0.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1703512084/tips/MDMT_flange_frqzl7.pdf[/url]

 

[DominicLee]

Thanks for this interesting solution!

 

[GD2]

OP,
UCS-66(c) is very clear on the standard flanges - B16.5 and B16.47. Appendix-2 flange design is generally considered for non-standard flanges. Using Figure UCS-66.3 for the governing thickness determination and then the impact test exemption curve Figure UCS-66, one can determine the minimum MDMT without a impact test for Appendix 2 flanges.

GDD
Canada

 

[Geoff13]

I am not surprised the B16.5 exemption temperature is different than the UCS-66 calculated temperature.

The B16.5 flanges are independent of the Code, and existing long before UCS-66 was added. The pressure-temperature ratings of B16.5 flanges do not meet the calculations in Appendix 2. Sometimes App 2 would say a thinner flange could work, and other times a thicker flange is required. However the B16.5 flange ratings were determine long, long ago and have proved themselves to be adequate, even when the calculation would say otherwise.

Similarly, the B16.5 exemption temperature is not calculated per the UCS-66 rules. It is also a value that has been shown to be OK through years of successful service long predating UCS-66. Up until recently the B16.5 ferritic flanges were exempt to -20°F (-29°C) regardless of heat treatment and FG practice. I think it's an excellent improvement to limit the more basic specs to only 0°F (-18°F).

In summary, the B16.5 flanges are acceptable for use as stated in the Code, but you shouldn't expect that they follow the Code rules.

 

[mechengineer]

@Geoff13,
Agree with your thoughts.
However, except UCS-66 (c), now it is easy to get the MDMT by using "g0" (governing thickness) and UCS-66 curves for B16.5 flanges. If I am an user, or in design view, I will request the strignent one.
For B16.5/B16.47 flanges (CS), as per UCS-66 (c), MDMT is -18 deg.C (g0=14 mm as per Curve B) for forged condition and MDMT is -29 deg.C (g0=18 mm as per curve C) for fine grain practice and normalized.
For forged condition of B16.5 flanges, the MDMT will not meet the requirement UCS-66 cueve B if g0> 14 mm.
For fine grain practice and normalized of B16.5 flanges, the MDMT will not meet the requirement UCS-66 cueve C if g0> 18 mm.

 

[r6155]

What is the Design Temperature of the pressure vessel?

Regards

 

[mechengineer]

This situation is somewhat similar to UG-20 (f). I called it “experience method”. In my view, UG-20(f) and UCS-66 (c) may be applicable for the components without the calculated MDMT by using UCS-66 curves. It is worth noting that most of clients (EPC/user)do not allow using UG-20(f). IOGP-619, clause 5.4. "Use of non-impact tested materials as allowed by ASME BPVC, Section VIII, Division 1, UG-20 (f) shall not be permitted".
In my opinion, UCS-66 (c) may be only applicable for g0<=14 mm for forged condition and g0<=18 mm for fine grain practice and normalized if there is not the MDMT calculation provided.
Also, it is certain that it is technically feasible to use UCS-66 curves and g0 getting the MDMT for B16.5 flanges, which is more accurate and safe.

 

[r6155]

The attached example does not make sense for a DT of 80°C.
Talk about impact testing, for what?

Regards