RE: MILL TOLERANCE

From: <James>
Date: Tue Apr 20 2004 - 09:52:00 EDT

George,

As you have posted this twice, I take it that you really want a reply?

To reiterate my first message the mill tolerance should be taken from the *nominal* wall thickness not the calculated minimum thickness.

Your calculation is still incorrecet as it is based on the calculated thickness, unless you are ordering controlled bore pipe which is a whole different ball game, your vendor will be asked to supply a scheduled thickness to ASME B36.10, your vendor will base the minimum allowable wall thickness on the schedule thickness and not your calculated thickness.

As stated previously the pipe with a calculated thickness of 9.70mm is shown to be non-compliant if the mill tolerance of 12.5% is taken from the nominal thickness. The

The minimum wall thickness is used in the calculation of reinforcement for branches in ASME B31 codes, ASME III and BS806. It is also used for calculating the transverse pressure stresses at branch connections: BS806 Eq 37. I don't have any of the ASME codes on my desk at the moment, but IIRC they also use the minimum tolerance thickness or the actual measured thickness (if known).

Barbara

-----Original Message-----

From: George Varghese [mailto:george@atkins-shj.ae] Sent: 20 April 2004 14:14
To: <a href="/group/PipingDesign/post?postID=4zz3N5y5YsRCYeSg8JXQ9LpE_V1aXg4QWZNKNr9Hu3WwST35yyWpxv9IG3-PeJnlSir_Zqges6tJcrH0gxYNUXFFxtSR-w">PipingDesign@yahoogroups.com</a> Subject: RE: [PipingDesign] MILL TOLERANCE

For example a 6" Sch 80 pipe - Nominal wall thickness is 10.97mm. 12.5% of 10.97mm is 1.37mm.
If this is taken from the nominal thickness, the minimum wall that is within tolerance is 9.60mm. That means the pipe vandor can supply the pipe with 9.60mm thickness which is in line with the pipe specification.

If the minimum calculated thickness is 9.70mm, this pipe will not serve the purpose. Considering the -12.5% mill tolerance, thickness should be 9.70/(1-.125)=11.1mm, hence a higher nominal thickness is to be selected.

From Caesar II manual: For most piping codes, the minimum wall mill tolerance is only used during the "minimum wall thickness" computation. Mill tolerance is usually not considered in the flexibility analysis.

George

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[Non-text portions of this message have been removed] Received on Tue Apr 20 09:52:00 2004