### Mill Tolerance - ASME (mechanical) Code Issues - .

07/02/2012· According to my understanding, Mill Tolerance is the tolerance for variation in the thickness of pipe from nominal pipe thickness which is 12.5% according to B31.3. i.e for NPS 10" and thickness 6.35 mm it is 0.794 mm Now from the ASTM material specification sheet of A358 we have "8.1.4 Thickness—The minimum wall thickness at any point in the pipe shall not be more than 0.01 in. [0.3 .