First, I am looking for the differences in Hot Rolled ERW tube and Structural Pipe.

So far I have found the following:

1. Structural Pipe is pipe which has been rejected for one or more defects which will affect it’s ability to safely hold pressure

2. The YS for pipe is lower than tube for a given material

3. Pipe is made by the same hot rolling and ERW process as tube.

Are these three Statements correct? What other differences are there (metallurgical, structural, processing, condition)? Why is pipe “weaker” than tube when you have the same material and same method of manufacture?

Second, I am looking for a reason to the fact that a given grade of HREW has a lower YS than the same grade DOM. Is this just a result of the cold working the tube sees in the DOM process or is there something else to the equation?   

Thanks for the info.

Pete