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moizpk2001 (Mechanical) (OP)
27 Mar 08 2:52
What are the size tolerances on OD & ID of say 8 Nom SCH 40 pipe.
JohnBreen (Mechanical)
27 Mar 08 9:38
moizpk2001

It depends on several factors.

According to ASME B36.10M it depends upon the Standard to which the pipe is being procured.

Assume that your pipe is ASTM SA-106 Seamless carbon steel pipe:  There is a permissible variation (in the SA-106 specification of the ASME B&PV Code, Section II) on weight per foot, diameter and thickness.  

Considering diameter and wall thickness: if you are procuring NPS 8, Schedule 40 pipe to ASME Standard SA-106, the outside diameter may vary no more than 1/16 inch over and 1/32 inch under the specified OD of 8.625 inch.  The minimum wall thickness at any point shall not be more than 12.5 percent under the nominal thickness specified.

So you have to look at the specification for the specific pipe that you are procuring.

Regards, John.
JLSeagull (Electrical)
27 Mar 08 11:18
Although this thread is posted under ASME the question could apply to other piping specifications such as API 5L line pipe.  API SPEC 5L includes tables that publish tolerances for diameter at pipe ends, wall thickness, weigh, lengths, coupling dimensions.
kalmari (Mechanical)
8 Apr 08 11:56
For this issue it's useful to know that in most cases the pipes of boiler proper (Section I) can have +/-1% O.D.(or I.D.) tolerance instead of the dia tolerances specified in material specifications.
+/-1% OD tolerance is common for pipe standards e.g. in Europe and so common practice also for many pipe manufacturers outside U.S.  
lgracio (Mechanical)
10 Apr 08 9:15
I would suggest you review ASME SA 530 or ASTM A 530 Specification, titled Specification for General Requirements for Specialized Carbon Steel and Alloy Steel Pipe. This specification provides the requirements for under tolerance of pipe wall (12.5%) and OD variations based on the NPS designator.

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