Piping Mill Allowance

The thickness of skelp linearly rolled into pipe is tightly enough controlled that a 12.5% allowance is not needed. But then the seam must be welded, so a weld efficiency could come into play. I'm not sure, but I understand that ERW (electric resistance welding) can be considered 100% efficient.

Seamless pipe requires extrusion over an external mandrel, whose center could vary 12.5% from the center of the die from which the extruded material emerges. Hence the 12.5% deduction for seamless forms.

I don't know if this is a fully correct explanation. Moreover, it takes some visualization to figure out what is really going on.

A better explanation would be most welcome.

Thank you for the detailed answer (I rate it GOOD ANSWER). What do you recommend using for "the reduction in thickness due to forming" ?

GA!

It should also be noted that many of today's tube/pipe consumers require tighter tolerances than the various standards require.

Having worked in the Welded Tube & Pipe Industry pretty much my whole life, with equal time split between working for an OEM designing Mills and working for tubing producers, half-ASTM Standard is the norm for about 95% of our customer base. And about 40 to 50 percent of those require tighter-than-half.

The majority of the tubing, not sure about pipe, that is supplied direct from the mill to the customer requires tolerances far tighter than current standards require. Generally those orders that are simply per-standard, are orders for Service Centers such as Ryerson and E.M. Jorgensen. Because, if you just wanted standard tubing or pipe, you wouldn't buy mill-direct unless you were looking at significant volumes.

JavaHead