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ValveEngineer123 (Mechanical) (OP)
6 Jan 09 10:51
The ASME B&PV code gives an eq'n to calculate minimum required pipe wall thickness for given pipe dimensions (OD,ID), design pressure and allowable stress on the pipe material.  The eq'n also includes an 'A' factor, which is to account for additional thickness required for, say, material removed due to threading.  For taper threads, the A value to be used is the thread depth.  This seems only to account for the thread depth, neglecting the taper of the thread itself.  Is the assumption in the code that NPT connections will be engaged all the way to the vanish threads and therefore the wall thickness reduction due to taper is not an issue?  Or is there a section of the code which allows one to neglect the wall thickness variation due to the taper entirely?  Any advice would be much appreciated.
nickelkid (Mechanical)
6 Jan 09 11:31

Which section of the code are you using?
ValveEngineer123 (Mechanical) (OP)
6 Jan 09 11:46
Section III
nickelkid (Mechanical)
6 Jan 09 12:48

A = an additional thickness to provide for material removed in threading, corrosion or erosion allowance, and material required for structural strength of the pipe during erection, as appropriate, in.

If the thread is in accordance with B2.1

[Pipe OD - (PD @ Beginning Thread - Height of Thread)] / 2

= Contribution to A from NPT thread   
ValveEngineer123 (Mechanical) (OP)
6 Jan 09 13:06
Thanks RCHandy, I can see that this is the approach that has been typically taken for dealing with taper threads.

What I am wondering is: does the code require one to consider the gradual reduction in wall thickness due to the taper itself?  If the mating (female) fitting does not engage the entire thread (up to the vanish threads), theoretically, there will be a minimum wall thickness less than that calculated using the method you described above.

Any thoughts?

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