B-366 UNS N06625 Allowable Stress per B31.3

[MEDK]

Piping Code: B31.3
Material: Incoloy 625
Fittings: B-366 UNS N06625

I am writing a piping specification for Incoloy 625 and am specifying the pipe wall thickness. There are allowable stresses for pipe B-444 UNS N06625 and forgings B-564 UNS N06625 (4" and smaller). I have not found any allowable stresses for Butt Weld fittings. From what I can tell, the appropriate material specification would be B-366 UNS N06625. Am I missing something and not looking in the right area? I am wanting to compare the allowable stresses between the piping material and the fitting material per the Code references.

Any response or direction would be appreciated.

MEDK

 

[doct9960]

MEDK,

You could probably use the allowable stress values in Table 1B of ASME Section II, Part D. SB-366 (UNS N06625) is listed in there.

 

[MEDK]

doct9960

Thanks for the response.

MEDK

 

[JohnBreen]

MEDK

Suggest that you peruse the B31.3 Code and become VERY familiar with weld joint strength reduction factors.

JB

 

[MEDK]

Mr. Breen:

Thanks for taking the time to reply. I am also familiar with your postings on the Caesar 2 discussion boards.

Assuming your reference is to the 'W' term, I am familiar with its use. This material application is not for high temperature, but for its corrosion resistance to the process fluid. Hopefully, I have not missed your point.

My concern, though, is that I cannot find a material listing in the allowable stress tables in B31.3 Code for an Alloy 625 butt weld fittings. I believe I need this information per the Code to determine the suitability of the fittings thickness in relation to the pipe wall thickness for the required design pressure. As suggested above, I could use the ASME Section II values, but Vessel Code allowables can be lower than the Piping Code allowables. At least that is the case when comparing the Alloy 625 piping material between the two Codes. I believe you are associated with the B31.3 Committee. So do you know why there is not a butt weld fitting material listing for Alloy 625? At this time, the only apparent approach is to use the lower values in the Vessel Code.

Thanks again for your time.

DK

 

[JohnBreen]

Hi Don,

I know this is not answering your question, but at the moment I do not have the answer. Why do you need the allowable stress for N06625? B31.3 does not require minimum wall thickness calculations for B16.9 elbows.

John

 

[JohnBreen]

Don,

I guess my point is that you DO NOT specify the wall thickness for standard butt welding elbows - rather you calculate the required wall thickness for the straight pipe using paragraph 3-4.1., round it up to the next schedule (including allowances for mill tolerance, corrosion erosion, etc) and specify the elbows to be the same schedule as the pipe. The B16.9 standard DOES NOT standardize the wall thickness of welding fittings; they must simply be able to pass burst tests. You do not use the B31.3 paragraph 301.2.1 pipe bend equations for standard elbows. In fact, in many cases, if you bought a new B16.9 elbow of a specific schedule and measured the wall thickness, you would discover that the thickness calculated by paragraph 301.2.1 would not be met by the new elbow.

Regards, John.

 

[MEDK]

Mr. Breen:

Unless I am misunderstanding paragraph 302.2.2, I believe I need to compare the allowable stresses for the pipe with the allowable stresses for the fitting material to comply with the referenced paragraph. If the fitting allowable stress is equal to or greater than the pipe allowable stress, then the pipe wall thickness calculation as you have pointed out will be sufficient for the fitting. Therefore the need for the N06625 fitting allowable stresses.

I fully agree if you use the calculations for a bend wall thickness, the actual elbow wall thickness may not meet the calculated results.

I do appreciate your time and your advice.

Thanks,
Don