Causes of Manufacturing Undertolerance in Piping

[CSGWB]

Could someone fill me in on what the primary causes of wall thickness variation leading to the 12.5% thickness tolerance in seamless pipe? My understand was that it was due to the relative movement of the maundrel during the forming process. Is this the case or is there another mechanism that causes this variation?

Thanks

CSGWB

 

[Carburize]

Mandrel and die wear also contribute plus there is a small effect from differences in alloy chenmistry.

 

[codeeng]

Getting the hole in the middle (concentric) is the primary reason for the tolerance. Otherwise the weight is generally pretty accurate.