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SA-193 Gr.B7M bolt material used in Wet H2S service is not passing requirement of UG44b clause.

KD007

Mechanical
Sep 27, 2013
8
Hello All,

I have to design high pressure vessel as per Div 1 for wet H2S service in which bolt material requirement is to use 'M' grade material for bolt i.e SA-193 Gr.B7M. However when using UG44b for flange derating the B7M bolting is not fulfilling the requirement of having higher allowable strength than SA193 B8 Cl.2.

Kindly advise if there is any other CS bolt alternative with higher allowable strength and availability in M grade for sour service.?
 
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Have you considered the usage of Code Case 2901?
As for the bolt material, we use SA354 Grade BD when need higher strength (steam service)
 
Code case 2901-1 won't help you - it has the same bolting restrictions. Do you need to go with B7M bolting? Or would B8 bolting suffice?
 
Code case 2901-1 won't help you - it has the same bolting restrictions. Do you need to go with B7M bolting? Or would B8 bolting suffice?
Hello TGS4, Yes you are right code case 2901-1 wont help. The vessel which I am designing is carbon steel vessel for which I guess typically we have used B7M bolting only. Can we use B8M (S.S) bolting in CS vessel with wet H2S service?
Isnt there any other CS bolting grade with higher allowable to be used for sour service?
 
Any suggestions on above query based on your experience with sour service vessel with high pressure? Need your expertise on same.
 
What is your purpose for not using B7M bolting in this service? The bolts will not (or, at least should not) see the process.
 
What is your purpose for not using B7M bolting in this service? The bolts will not (or, at least should not) see the process.
Hello TGS4, With B7M bolting I am getting error for UG44b clause error message. Also as per client specs they have mentioned to use bolt with "M" grade for H2S service. Also same bolts have been used in connected piping PMS specs.
Have you used any other higher allowable CS bolting material for H2S service in your experience to avoid the Deficiency in COMPRESS software?
 
I have seen end users that require "M" bolting on sour service so that incase there was a leak there would be less risk of catastrophic failure.
 
Or you can evaluate nozzle loads on flanges using mandatory appendix 2 method instead of UG-44(b) and mantain grade B7M material.
Axial force and resultant bending moment are converted into an equivalent pressure and added to the design pressure of the flange for the calculation.
In my experience this has always been accepted both by ASME inspector and final client.
 
Or you can evaluate nozzle loads on flanges using mandatory appendix 2 method instead of UG-44(b) and mantain grade B7M material.
Axial force and resultant bending moment are converted into an equivalent pressure and added to the design pressure of the flange for the calculation.
In my experience this has always been accepted both by ASME inspector and final client.
Hello Si-bo, Thanks for the reply. Above solution can be practical for large flanges however it would not be viable solution to design standard small size flanges i.e from 2" to 14" as per Appendix 2 everytime when the no of flanges is more in equipment.
I just need alternative higher strength bolt material in Grade M to satisfy UG-44b requirement.
 
Is your flange insulated? Cold service? Is it high severity wet H2S service? Maybe you still can use Gr. B7 if it is an external bolting with unrestricted air circulation.
 
Is your flange insulated? Cold service? Is it high severity wet H2S service? Maybe you still can use Gr. B7 if it is an external bolting with unrestricted air circulation.
B7M bolting requirement is coming from client specs only.
 
"M" grade is the common industrial practice for wet sour service to prevent stress corrosion cracking. This is also in NACE. Please do not argue with it. We use "M" grade for numerous wet sour service vessels.
Do not use SS to CS flange, not just the galvanic corrosion, but also the different thermal expansion that you will never ever seal it up, and eventually, rupture your bolting by over-tightening.
What is your bolt size ? Allowable stress is based on the bolt size.
The last, ignore UG-44(b)(3), it makes no sense and shall be lifted from the code. So many "M" grade using around the world, and never heard of any issue from piping load.
So still apply the code equation but ignore that dummy restriction. Your flange rating is still based on pressure-temperature rating table, nothing to do with "M" grade.

And the last of the last, never ever justify standard B16.5/B16.47 flange by Appendix 2. Whoever asking you to do so, he is not qualified as a vessel engineer.
 
B7M bolting requirement is coming from client specs only.
Both NACE MR0103 Sec. 16.2 and NACE MR0175 Part A.2.2.4 specifically require it only for "exposed to sour service" bolting which are "denied direct atmospheric exposure". If your specs refer to NACE, then you can take that exception if the flange bolting is not insulated. Client specs like Shell DEP only require M bolting for high severity services when the flange bolting is exposed to the atmosphere and uninsulated.

Is your service high severity wet H2S?
 
"M" grade is the common industrial practice for wet sour service to prevent stress corrosion cracking. This is also in NACE. Please do not argue with it. We use "M" grade for numerous wet sour service vessels.
Do not use SS to CS flange, not just the galvanic corrosion, but also the different thermal expansion that you will never ever seal it up, and eventually, rupture your bolting by over-tightening.
What is your bolt size ? Allowable stress is based on the bolt size.
The last, ignore UG-44(b)(3), it makes no sense and shall be lifted from the code. So many "M" grade using around the world, and never heard of any issue from piping load.
So still apply the code equation but ignore that dummy restriction. Your flange rating is still based on pressure-temperature rating table, nothing to do with "M" grade.

And the last of the last, never ever justify standard B16.5/B16.47 flange by Appendix 2. Whoever asking you to do so, he is not qualified as a vessel engineer.
Hello jt1234,
Thankyou for feedback. Just to clarify I would be for sure using "M" grade bolting for application, just wanted to know if there are other higher strength Carbon steel bolting material except SA-193 Gr.B7M and SA-320 Gr.L7M which we can use in Sour service/H2S service requirement for both standard and App.2 designed flanges.
 
"M" grade is the common industrial practice for wet sour service to prevent stress corrosion cracking. This is also in NACE. Please do not argue with it. We use "M" grade for numerous wet sour service vessels.
Do not use SS to CS flange, not just the galvanic corrosion, but also the different thermal expansion that you will never ever seal it up, and eventually, rupture your bolting by over-tightening.
What is your bolt size ? Allowable stress is based on the bolt size.
The last, ignore UG-44(b)(3), it makes no sense and shall be lifted from the code. So many "M" grade using around the world, and never heard of any issue from piping load.
So still apply the code equation but ignore that dummy restriction. Your flange rating is still based on pressure-temperature rating table, nothing to do with "M" grade.

And the last of the last, never ever justify standard B16.5/B16.47 flange by Appendix 2. Whoever asking you to do so, he is not qualified as a vessel engineer.
Regarding your opinion on UG-44(b)(3) not making sense, I would refer you to PVP2013-97814 where you will find the reasoning on why this restriction exists.
 
And the last of the last, never ever justify standard B16.5/B16.47 flange by Appendix 2. Whoever asking you to do so, he is not qualified as a vessel engineer.
If you are referring to my comment, evaluating external loads on nozzle's flanges (B16.5) with appendix 2 is generally allowed and accepted by many clients and final users. Most of the contractor's specifications allows both UG-44(b) and Appendix 2 methods, at least in the petrochemical industry.

I'd like also to point out that ASME UG-44(b) states "external loads may be evaluated ..." which means it's not a mandatory requirement; in my opinion, the best alternative to UG-44(b) is the appendix 2 if you want to stay within the code. Other methods such as Kellogg can be used but, as previously mentioned, you fall outside of the code and this may not be accepted.
 

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