Guys (& B)
has anyone measured the as-delivered minimum wall thickness on a batch of pipe? I would be interested to know the range, as 12.5% seems like a generous tolerance in this day and age. Seems a little crazy paying for, for example, 10mm and being forced to settle for 8.75mm. Pipe generally has a weight tolerance as well; A106 is +10% - 3.5% (A53 +/- 10%) so the difference is presumably density and concentricity variations. My interest is if these limits are truly required by the pipemakers or if they are just historical numbers and the makers aim at the lower limit.
Cheers
Steve
-----Original Message-----
From: George Varghese [mailto:george@atkins-shj.ae]
Sent: Wednesday, April 21, 2004 7:03 PM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] MILL TOLERANCE
Barbara,
I never intended to send the message repeatedly. I received a "mail could
not be delivered" notification for this message. Hence I sent the message
again.
Please note that I was also reiterating that the mill tolerance should be
based on the nominal thickness, not from the calculated thickness. I was
not adding 12.5% of calculated thickness but finding a thickness with
inbuilt 12.5% MT (that is why I divided the calc thk with 0.875) and
commercially available. In either method, for a calculated thickness of
9.7mm, the thickness selection (with MT) according to ASME B36.10 will lead
to a higher schedule than Sch80.
Once again I sincerely regret any inconvenience caused to anybody by
repeatedly sending the message, even if unintentionally.
Thanks
George
-----Original Message-----
From: James, Barbara [mailto:bjames@mitsuibabcock.com]
Sent: Tuesday, April 20, 2004 5:52 PM
To: 'PipingDesign@yahoogroups.com'
Subject: RE: [PipingDesign] MILL TOLERANCE
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: PipingDesign@yahoogroups.com
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
Yahoo! Groups Links Received on Wed Apr 21 04:19:00 2004
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