B16.9 elbow thickness 2

[pipe15]

We specified and ordered elbows with the following description:

90 DEG LR ELBOW, S-40S, BE, ASTM A-403 GR WP304L, SMLS, B16.9

The vendor fabricated the elbows by bending S-80S pipe and then counter-bored the ends to match the S-40S connecting pipe. The vendor than stamped the elbows as being S-40S.

The vendor is pointing to a sentence in B16.9 to justify what they did. It is:
In order to meet design or manufacturing requirements, it is expected that some portion of formed fittings may have to be thicker than the pipe wall with which the fitting is intended to be used.

Further, B16.9 states:
6.2.2 Bore Diameter. Bore diameters away from the ends are not specified. If special flow path requirements are needed, the bore dimensions shall be specified by the purchaser.

We believe we should not have to specify the S-40S bore as a 'special' requirement and that we are justified to believe that the elbows should have been supplied as S-40S.

The analysis for the pipelines may not be conservative based on the as-supplied fittings. They are heavier, stiffer, and do not have the same flow area.

So, is this a common vendor practice? What experience do others have regarding this issue?

thanks
Mark

 

[racookpe1978]

Never heard of it before.

If heavier, stiffer, and not carrying the "design" expected flow you get from your Sch 40 calculations? Reject them.

 

[dcasto]

Pipelines do this all the time to get compound S bends.

 

[uaepiping]

I believe, when taking a pipe of 40S and stretching to make it an elbow, the extrados will have less thickness, than 40S. So heavier thickness is required to work on.
Also as you mentioned ASME B16.9 alerts that the thickness can be heavier.
So in my opinion (if flow area reduction is not causing much of a problem), then you should accept this elbow.
In stress analysis, there will not be significant difference. If you doubt this, then do one thing, as you are in procurement phase, this means engineering is already done and you would have the stress model. Model these elbows with heavier thickness and then check the result.

 

[RoboCop16]

pipe15,

You can't expect a ASME B16.9 fitting to have the specified wall thickness at all points, only at the connecting ends. That some parts of the fitting will have a heavier wall thickness is pretty much a given. The manufacturer should probably strive to maintain the ID and have the extra wall thickness on the OD if practical, but it is not a B16.9 requirement. ASME B16.9 in section 6.2.2 states: "Bore diameters away from the ends are not specified. If special flow path requirements are needed, the bore dimensions shall be specified by the purchaser". If you didn't specify the internal bore away from the ends, I don't see how you can reject the fittings.

Anyway, unless you have some super-sensitive system, I wouldn't think that the wall thickness increase that you describe can be much of a pressure drop concern, .

Also, the manufacturer must demonstrate the pressure design of the fitting, either by calculation code or by proof test. It is likely that these elbows will pass, as the manufacturer has - wisely, as it seems to me - decided to make them from a higher wall thickness than the connecting pipe.