For years, prior to getting into the steel industry, I was always scratching my head wondering how steel pipe was made. Almost everyday, I would wake up, brush my teeth, then go directly to my thinking chair and ponder the very existence of steel pipe and the process behind it manufacturing. Okay…that’s a lie. I never really thought about it that much but, I am willing to bet that someone out there, somewhere, at this very minute is thinking to themselves, I wonder how steel pipe is made? That could be a stretch too, but let’s just get to it.
Steel pipes are generally made in 21’ and 42’ lengths. There are a variety of uses for structural pipe, but generally there are only two processes that are used to make this pipe. These processes result in one of two types of pipe, welded pipe and seamless pipe. Let’s first look at continuous weld pipe.
Continuous Weld Pipe
The process of making continuous weld pipe starts with raw coiled steel, known as skelp. Depending on the size and thickness of the pipe, the skelp can come in various width and thicknesses. Coils are welded together, end to end, to produce one continuous run of steel. This continuous run is then fed through a roll leveler and then straight into a gas fired furnace where it is heated to the proper temperature for forming. It is then formed into an oval shape as it passes through the ends of the furnace. Once the oval coil is hot enough, it is pressed firmly together by welding rolls to produce a forged weld. Combined with the heat of the furnace, the pressure exerted from the rolls is what produced the weld on continuous weld pipe. The final step in the process occurs when the pipe is still hot; it is fed through one more roll where it is reduced in diameter and wall thickness to make the proper dimensions required. Continuous weld pipe usually comes in one of three weights, standard, extra heavy and double extra heavy. NOTE: Some lighter weights are available in certain diameter pipes. Let’s see how seamless pipe is produced now.
The process of making seamless pipe is very different than that of making continuous weld pipe because it is produced without a seam in the pipe. In order to obtain a seamless product, the material must be stretched instead of rolled. Like the continuous weld pipe, the material start with raw coiled steel, known as skelp, that is then welded end-to-end to create one long continuous run of steel ribbon which is then fed into the mill equipment. It is then heated to the proper temperature, and fed through various rollers to stretch the material to the proper dimensions. Larger seamless pipes are produced by piercing a solid billet of deoxidized and conditioned steel that has been properly heated to the perfect temperature. It then gets processed through a series of mills where the pipe is finished to the correct dimensions. The seamless pipes goes through a much more stringent finishing process that includes straightening, inspection, testing and end finishing.