Hoop Shrinkage on B31.3 Stainless Piping

[lsone]

All, I have an issue and would like to present it correctly.

Code of construction is B31.3 normal. Client specs/standards do not address hoop shrinkage. B31.3 has an interpretation 25-27 that reads as follows...

Question: Does ASME B31.3-2012 provide an acceptance criterion for the amount of base material deformation adjacent to butt welds, commonly referred to as "hoop shrinkage," shown in the following diagram?
Reply: No

Ive been on projects where the client specs outline a max/min acceptance for hoop shrinkage, some times called radial shrinkage in the verbiage.

Now my approach;

ASME Section II Specification for Seamless and Welded Austenitic Stainless Steel pipes is a supplement to B31.3 code. SA-312 within Section II references A999/ A999m which is Specification for General Requirements for Alloy and Stainless Steel Pipe. A999 section 12 has Table 1 that shows Permissible Variations in Outside Diameter. Pipe is 16" Sch10. Now based on the table and some of the verbiage within, we are allowed to be 1/32" under on the outside diameter. It is expected that ASME Section II material manufacturing specifications are maintained and all material remains in its intended, unmodified and purchased condition post welding.

Am I off side? Im not super happy with the tolerances as 1/32" on a diameter is 1/64" radially and this could open up a massive can of worms. Right wrong or indifferent. A little common sense goes a long way and that's why having the client spec with a max radially shrinkage is nice to have.

Thank you

 

[gwalkerb]

I don't know if I would agree with this statement.

> all material remains in its intended, unmodified and purchased condition post welding.

The details from A999/A999M Table 1 are for the material in its as-delivered state, it's not intended as permissible variations to the material after any fabrication process. In fact, it's impossible to have a material in this state post-welding - at a minimum, there's always HAZ on both sides of the weld, so I wouldn't look at the material specs for information about hoop shrinkage.

It sounds like you need to develop your own shrinkage standards that you can use when your customers don't have their own - if you have previous client specifications that provide limits, that would be a good starting point, although I'm sure you're looking for some theory on how to determine said limits. I can't help you there unfortunately, but it doesn't appear that there's any specific code requirements, so you can take whatever approach you want.

 

[weldstan]

There will always be plastic deformation of the base material that thin in arc welding and austenitic stainless will have greater deformation than carbon and low alloy steels. As gwalkerb stated above A-999 is not applicable in your case. You will have to develop some manufacturing/welding methods to minimize distortion. I have seen plasma arc and single pass pulsed GTAW provide lowest deformation in similar arc welded joints.

 

[lsone]

I forgot to put some quantifiable findings. On the 16" joint, .125" radially, so .25" overall diameter reduction post welding. On another weld roughly .25" radially, overall .5" overall diameter reduction.

Im no stranger to welding and stainless as I was a pressure welder. I understand why and how it happens. Just difficult to approach from a quality side when the code of construction doesn't cover it and the client spec also does not address it. Operations teams always bring this up as it creates turbulence in process flow which has its whole bag of concerns.

Also, 95% of the joints welded have zero deformation. Im talking hundreds of welds.

 

[DriveMeNuts]

It sounds like you have a Process Engineering problem rather than a Mechanical Engineering Problem.
As a result, I wouldn't expect to find a solution in a Mechanical Code.
As suggested above, perhaps you need to develop an internal specification to deal with this issue.