Butt weld fittings

[LeoSter]

We have an 8x6 XS reducer measured 0.5 on the 8" side and 0.62 - 0.65 on the 6" side. Is that too thick on the 6" side? are they usually manufactured that way?

 

[JohnWE]

It appears to be manufactured incorrectly on the 6" side. The wall thickness on that side should be 0.432.

 

[gwalkerb]

Assuming this is a ASME B16.9 fitting, you can check the allowable tolerances from that standard (Table 11-1). Between NPS5 and NPS8, the tolerance on outside diameter is +0.09"/-0.06", while the tolerance on inside diameter is +/-0.06".

Nominal outside diameter for NPS6 is 6.625". With tolerance this could be as large as 6.715".
Nominal inside diameter for NPS6 XS is 5.761". With tolerance this could be as low as 5.701".

Therefore the maximum allowable wall thickness for a B16.9 NPS6 XS fitting would be (6.715" - 5.701") / 2 = 0.507". Your fitting is non-compliant to B16.9 and should be rejected.

The manufacturing process for these types of fittings typically starts with one size of pipe, and then expands or contracts one end to the required size. I suspect they started with NPS8 XS pipe, contracted one end to NPS6 OD, but didn't remove or check the extra material, as the area of the cross section of NPS8 XS pipe is similar to the area of NPS6 pipe with a 0.62"-0.65" wall.

 

[LeoSter]

Assuming this is a ASME B16.9 fitting, you can check the allowable tolerances from that standard (Table 11-1). Between NPS5 and NPS8, the tolerance on outside diameter is +0.09"/-0.06", while the tolerance on inside diameter is +/-0.06".

Nominal outside diameter for NPS6 is 6.625". With tolerance this could be as large as 6.715".
Nominal inside diameter for NPS6 XS is 5.761". With tolerance this could be as low as 5.701".

Therefore the maximum allowable wall thickness for a B16.9 NPS6 XS fitting would be (6.715" - 5.701") / 2 = 0.507". Your fitting is non-compliant to B16.9 and should be rejected.

The manufacturing process for these types of fittings typically starts with one size of pipe, and then expands or contracts one end to the required size. I suspect they started with NPS8 XS pipe, contracted one end to NPS6 OD, but didn't remove or check the extra material, as the area of the cross section of NPS8 XS pipe is similar to the area of NPS6 pipe with a 0.62"-0.65" wall.

This is very helpful, thank you! Since it's out of spec on the thicker side (more conservative?), what's the downside to tapering it to meet the requirement of B31.8 when welding it to the Sch80 pipe?

 

[Krausen]

There wouldn't really be any downside to taper boring the 6" side (per code requirements, typically max 3:1 taper), other than the additional time & work involved in that. This is done often when buttweld fittings are ordered with thicker wall than the component they're being buttwelded to

 

[goutam_freelance]

Typically butt weld high pressure valves will have much higher body thickness than pipe thickness. These are welded with tapered transition. See 'Figure 127.4.2-1 Welding End Transition — Maximum Envelope' of ANSI B31.1