Weld Neck Flanges 1

[Piping Hydro]

If we intend to use weld neck flange 56" , 600# , THK. 0.81" (ASTM A105N) with pipe 56" , API 5L , X70 , THK. 0.81" , is it applicable to weld them together and what is the precautions shall be taken in our considerations for this issue including welding , NDT and hydro static testing?

Note: MSS-SP-44 (Para. 5.3 & ANNEX A) says "the hub of weld neck flange shall has the same yield strength of the pipe" which is doesn't match the material we had as mentioned above, is there any one know any thing about this issue?

Thanks in advance....

 

[LittleInch]

If the 0.812 thickness is the main pipeline wall thickness determined by using the X70 strength, then no, the A105N flange neck is too thin.

That's why MSS-SP-44 exists to allow use of ASTM A694 F70 material which is the same yield strength as the pipeline wall thickness.

For some reason ASME B16.5 and its cousins don't list A694...

The only other way is to establish what the wall thickness of your 56" pipe would be if you used the yield strength of the flange and then insert that thicker pipe (made from X70)into the pipeline as a ramped spool piece / transition piece back to your 0.812. However that could reduce the ID considerably and make pigging an issue.

In reality people just order pipeline flanges to 16.5 or 16.47 to ASTM A694 F70 (in your case) and state the pipeline wt and it's all good. You should really order it to MSS-SP-44 to fully comply.



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[Piping Hydro]

Thanks for your kind response "LittleInch" , be noted the pipe has the same thickness of WNF (0.81")but they have different yield strength and as per material specs. certificate from supplier of WNF its yield strength is 363 MPa (~ 52 KSI) but the yield strength for pipe is 70 KSI , so the hub of WNF here is a weakness point comparing with the pipe depend on yield strength.

 

[LittleInch]

Errr, correct. Hence my response that welding the two 0.81" bits together is not applicable.

I don't know where you're getting 363 KPa yield strength from - normally 105 is 250 / 36 ksi. That is a minimum and maybe your particular flanges are actually a bit higher, but it's quite difficult to take advantage of that increase. Either way, it's not 70ksi.

So my response is the same - you can't just weld these two together and hope for the best.

Not with a 52" class 600 pipeline that's for sure.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Piping Hydro]

you are right the Min. SMYS of a105N is 36 KSA this is the min. required , but regarding to supplier certificate and after heat treatmeant it became 52 KSI , doesn't matter! I think there is no problem to weld the pipe and flange together taking in consideration the difference between two yield strength to select the proper filler and WPS for this welding process, but the big issue here from my point of view is the calculation of hydro test pressure shall be depend on the min. yield strength which here is the hub of WNF. that's right?

 

[BJI]

You are missing the point, it isn't about the min specification yield strength. The pipe has been sized based on a minimum required thickness for high strength material, therefore your hub wall thickness can't possibly meet the minimum thickness requirements unless the pipeline was excessively over sized, which won't be the case. Therefore, under all conditions, not just hydro, this is not acceptable. LittleInch has already answered your question quite well.

 

[Piping Hydro]

Gents, we had already welding neck flange and a pipe with the same wall thickness but different yield strength as per above specs.

 

[DekDee]

If you do not even understand that required hydrotest pressure is based on design pressure and not yield strength you should not be involved with what you are doing !!!

 

[LittleInch]

Piping hydro - you don't seem to be getting the point here so I'll make it a little clearer.

Going back to your OP:

"is it applicable to weld them together?" No

"what is the precautions shall be taken in our considerations for this issue including welding , NDT and hydro static testing?" - buy the correct flange made from material with the same SMYS as the pipe.

The "Big issue" here is that one part of your system ( the WN flange) is a lower strength than the connecting pipe, but the same thickness. The fact you have the flange is your problem - you need to get another one made from the correct material.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[KevinNZ]

There maybe there is some information missing here.
Does the system design pressure actually require X70 0.81" pipe? The A105 flange strength maybe OK and the X70 used just because they have some. What did the designer require on the drawings?
The system design needs to be reviewed. This is not a question about fabrication and hydro testing.

Even if the 0.81" WN is OK for the design pressure, what about the pressure rating of the actual flange in A105 compared to X70?

There some modifications that could be done to the WN flange but the options would be limited by the design code.

 

[Piping Hydro]

Thank you so much "LittleInch"
Dear "DekDee" you are right the test pressure is based on design pressure, but we have to ensure that hoop stress will be produced from test pressure doesn't exceed 100% of SMYS at any point.
Thank you for all sharing info.

 

[LittleInch]

So what are you going to do and why?

You started this and now you need to finish.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Piping Hydro]

Dear "LittleInch" , I offered my recommendation to use WNF, ASTM A707 instead of A105.