My introduction into welded pipe construction was in late 60's down in Baytown, TX in the oil refineries where I worked to save enough money for another semester of college up in Huntsville, TX.

I do not know if this will interest many inspectors or welders here but this chart gives an overview of the refinery process for those in the petrochemical field.

I cannot recollect where I obtained this chart but it is similar to the one found at www.setlaboritories.com