Process Equipment and Plant Design
Seamless pipe is made

By extrusion & casting into static and centrifugal molds
From rolled strips formed into cylinders and seam-welded
By forging a solid round, piercing it by simultaneously rotating & forcing it over a piercer point and further reducing it by rolling gas drawing
Both B and C

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Process Equipment and Plant Design
In the case of a shell and tube heat exchanger, the logarithmic mean temperature difference

Is always less than arithmetic average value
Is always less than arithmetic mean value, but more than geometric mean value
Is always more than arithmetic mean value and the geometric mean value
May be either more or less than geometric mean and arithmetic mean value depending upon whether the flow of stream is co-current or counter-current

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