Steel Pipes

The Manufacturing Process: Steel Pipes
Steel pipes are made by two different processes. The overall production method for both processes involves three steps.

First, raw steel is converted into a more workable form. Next, the pipe is formed on a continuous or semi continuous production line. Finally, the pipe is cut and modified to meet the customer's needs.

Pipe making
• Skelp is made into welded pipe. It is first placed on an unwinding machine. As the spool of steel is unwound, it is heated. Steel is then passed through a series of grooved rollers. As it passes by, the rollers cause the edges of the skelp to curl together. This forms un welded pipe.

• The steel next passes by welding electrodes. These devices seal the two ends of the pipe together. The welded seam is then passed through a high pressure roller which helps create a tight weld. The pipe is then cut to a desired length and stacked for further processing. Welded steel pipe is a continuous process and depending on the size of the pipe.

• When seamless pipe is needed, square billets are used for production. They are heated and molded to form a cylinder shape, also called a round. The round is then put in a furnace where it is heated white-hot. The heated round is then rolled with great pressure.

High pressure rolling causes the billet to stretch out and a hole to form in the center. Since this hole is irregularly shaped, a bullet shaped piercer point is pushed through the middle of the billet as it is being rolled. The pipe may still be of irregular thickness and shape. To correct this it is passed through another series of rolling mills.

Final processing
• After pipe is made, put through a straightening machine. Fitted with joints so two or more pieces of pipe can be connected. The most common type of joint for pipes with smaller diameters is threading, tight grooves that are cut into the end of the pipe.

The pipes are also sent through a measuring machine. Quality control data is automatically stenciled on the pipe. The pipe is then sprayed with a light coating of protective oil.

By galvanizing it or giving it a coating of zinc. Depending on the use of the pipe, other paints or coatings may be used.

Quality Control
X-ray gauges are used to regulate the thickness of the steel. The gauges work by utilizing two x rays. One ray is directed at a steel of known thickness. The other is directed at the passing steel on the production line. If there is any variance between the two rays, the gauge will automatically trigger a resizing of the rollers to compensate.

One method of testing a pipe is by using a special machine. This machine fills the pipe with water and then increases the pressure to see if it holds. Defective pipes are returned for scrap.

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