Pipe-and Tube-Forming Processes

Actually I should feel sorry for myself because I can't do the fasting for the whole days. I know the reason because I have problem with my stomach so I can't do it. But today I have to force myself to do it and to forget all the pain, it's better I post the Piping & Fabrication first before start another activity.

Pipe-and Tube-Forming Processes
There are basically two types of pipe- and tube-forming processes, namely, seamless and welded. Each process imparts unique properties to the pipe or tube. Seamless pipe or tube does not have the presence of a welded seam along the length of the pipe. This seam has traditionally been believed to be a potential weakness. The development of automated welding processes and quality control, however, has made this a virtually nonexistent concern. The control of thickness uniformity and concentricity is relatively easy with welded pipe and tube. In general, the seamless pipe is more expensive to produce. The classification of cylindrical tubular products in terms of either pipe or tube is a function of end use. This is discussed further under Tubular Product Classification.

FIGURE A5.2 Continuous casting process

Seamless Pipe. Seamless tube and pipe (Fig. A5.3) are manufactured by first producing a hollow tube which is larger in diameter and thickness than the final tube or pipe. The billet is first pierced by either a rotary (Mannesmann) piercer or by a press piercing method. For tubes of small diameter, the mandrel mill process is used. For medium outside diameter tubes of carbon or low-alloy steel, the Mannesmann plug mill process is used. Large-diameter, heavy-wall carbon steel, alloy, and stainless pipe is manufactured by the Erhardt push bench process and vertical extrusion similar to the Ugine Sejournet type extrusion process. High-alloy and specially shaped pipe are manufactured by the Ugine Sejournet extrusion-type process. These processes are performed with the material at hot-metal-forming temperatures. Further cold processing may or may not be performed to obtain further dimensional accuracy, surface finish, and surface metallurgical structure.

FIGURE A5.3 Seamless tube and pipe manufacturing processes

Mandrel (Pilger) Mill Process. In the mandrel (pilger) mill process (Fig. A5.4), a steel billet is heated to forging temperature and placed between the rolls of a hot rotary piercing mill. A piercing point is placed at the center of the billet, and the rotating rolls are designed to advance the billet over the piercing point, thereby forming a hole through the center of the billet along its entire length as it advances into the tilted rolls. A mandrel of outside diameter approximately that of the inside finished pipe diameter is pressed into the pierced hole of the billet. This combination of mandrel and billet is placed between rolls of a pilger-mill having a cam-shaped contour revolving counter to the direction in which the billet is being forced by means of a hydraulic and pneumatic ram mechanism.

FIGURE A5.4 Mandrel (pilger) mill process

In the pilger-mill, the rolls first grab the hot billet and after some rotation form a shaft. The pressure of the rolls forces the billet backward, and the resulting tube section is squeezed and smoothed out in the adjacent part of the roll groove. This process is equivalent to forging the billet against the mandrel and driving the billet and mandrel against the ram. After reaching the open portion of the cam shape, the ram mechanism again forces the billet into the rolls. Following the pilger mill process, the tube is reheated and passed through a reducer or sizer to provide a more uniform diameter. The resulting tube or pipe is called hot finished seamless.

The pilger-mill process is slower than conventional drawing. However, since large reductions in diameter are possible in a single pass, the process is applied to the production of tubes of small diameter such as heat exchangers, fossil fuel boilers, and nuclear steam generators