We must first explore the basics of piping and tubing in order to understand their differences. Tubing is designed in multiple shapes, including squares and rectangles. Round metal cylinder tubing looks very similar to piping and also offers structural purposes. The difference between tubing and piping lies in the manufacturing process.
Pipes are manufactured to the specifications of the American Society of Mechanical Engineers (ASME). Because of this, pipes can transport gases and liquids in addition to providing structural support. Tubes, on the other hand, are designed purely for structural application and, thus, cannot be used to transport a medium.
Fusion Weld or Continuous Weld
There are several processes for producing pipe. One process is called Fusion Weld, or Continuous Weld. During the fusion weld process, a ribbon of steel plate is heated in a furnace. Each ribbon has the appropriate wall thickness and width to meet the specifications of the finished product. The ribbon is then heated in a furnace and shaped by rollers into cylinder form before the two edges are fused together, thus creating a seamed pipe.
Electrical Resistance Weld
Another process used to manufacture pipe is the Electrical Resistance Weld (ERW) process. Like the fusion weld process, the ERW process shapes the steel ribbon with a series of rollers. However, deviating from the fusion weld process, the ERW process forms the coiled steel plate into a cylindrical shape without the use of heat. It is only afterward that heat from an electric charge is applied. This process welds the edges together.
The excess seam is then mechanically removed and additional heat is applied to normalize the seam area. The seam area of a pipe manufactured using the electrical resistance welding method is usually stronger than that of a pipe created using the fusion weld method.
Manufacturers may also produce Seamless Pipes. The process of manufacturing seamless pipes begins with a solid steel cylinder, called a round billet, or a tube round. The round billet is continuously heated and rotated, while the center is pierced and hollowed out to create a shell. The shell walls are then molded until they reach the desired thickness. Because heat is used through the duration of the formation process, the seamless pipe is fully normalized throughout its circumference.
Submerged Arc Welded and Double Submerged Arc Welded Pipes
Submerged Arc Welding (SAW) is a popular arc welding process. In submerged arc welding, the welding arc is submerged in flux during the welding process. The flux protects the weld seam area from atmospheric contamination during heating.
Double Submerged Arc Welded (DSAW) pipes are formed when two separate processes are used to create both inside welds and outside welds. DSAW pipes are manufactured in sizes, ranging from 16 to 144 inches. Their wall thicknesses typically vary from 0.250 to 1.5 inches.
Double submerged arc welding is the most common process today because of its superior strength and effectiveness. Double submerged arc welded pipes are manufactured in two processes called the pyramid rolls method and the U-O-E method. Additionally, they are available in two formats: straight and spiral weld pipe formats.
Double submerged arc welded pipes are applied in high pressure pipelines, as well as onshore and offshore oil transmission lines. They are also used in pipe piles. Industries using DSAW pipes include: the oil industry, the gas industry, the filtration industry, the refrigeration industry, the refining industry, the petrochemical industry and the offshore industry.