about manufacturer's tolerance of the wall thickness of pipes,fitting

[khaldacompany]

if i have 20" sch 60 , its nominal thickness is 20.6 mm and i measure it find it 25mm . why its thickness be increased its nominal hickness

 

[JoeTank]

Most piping specs are based upon a +/- 12.5% wall thickness tolerance. If the pipe is made from plate, it would follow a tol;erance for the plate.

Joe Tank

 

[KENAT]

khaldacompany

"why its thickness be increased its nominal hickness"

Because to routinely achieve the exact nominal thickness to within even typical machine shop measurement techniques would be prohibitively expensive.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[gr2vessels]

khaldacompany,
Most likely the 20" sched 60 pipe is not what you have specified, but it is a higher schedule like Sched. 80, with some undertolerance. The maximum tolerance for sched 60 pipe wall thickness would only allow for 20.61 x 1.125 = 23.19 mm, much less than 25 mm you have measured, I assume. If the pipe came with a certification claiming sched 60, when it is obviously a higher schedule, I would question the rest of the details also, including the composition and other relevant details. It sounds like a typical Chinese delivery...
cheers,
gr2vessels

 

[DiplingAndre]

First Question must be the Spec/Standard acc.the pipe is produced!
When the pipe is produced for e.G. acc. ASTM A 358 then you don't have a over tolerance.
You can only argue with the tolerances of the plate.

 

[march1971]

The following may be the reason:
(1)Most pipe specs, ASME B16 in particular, give a manufacturing tolerance of +/- 12.5%
(2) It coud also be that you did not identify the schedule of the pipe correctly.
(3) Most impotantly, the calibration of the tool used in carrying out the measurement might not have been correct or the tool might have been calibrated using a material having a grade different from that of the pipe and/or under a different environmental condition(temperature).

If the measuremnt was carried out using a UT set, the temperature of the material and that of the surrounding will have a significant effect on the measurement result.

Also the operators skill have effect on the end result(especiall ability to align probe properly).

Another thing that could affect the result is the measuring range of the instrument and its operating conditions.