ERW (Electric Resistance Welding) is a process used to manufacture pipe, and the result is ERW pipe. These pipes can be identified by looking for a stencil on the side of the pipe that says “Type E.” The American Society of Mechanical Engineers (ASME) provides the guidelines and specifications for all pipe manufacturing, meaning that pipes manufactured using the ERW process can safely transport gases and liquids as well as provide structural support. The main use of ERW stainless steel pipe is in low to medium pressure applications. A common example would be the transportation of water or oil. Another common use of this type of pipe is pipe piling and in the cable pipe systems.
The process of manufacturing ERW pipe uses high-frequency induction welding technology (up to 21 inches OD). This pipe size varies from 2 ⅜ OD to 24 inch OD and can be just about any length all the way to 100 plus feet. These pipes can have surfaces finishes. Finishes can be bare or they can come in a coated format, whatever better meets the needs of the customer.
A quick summary of the process is that steel ribbon is shaped using rollers, then formed into a cylindrical shape using heat and then finally the edges are welded together with an electrical charge. However, the process is much more extensive than that and is explained below.
First, ERW stainless steel pipe is manufactured using HR coils. These HR coils are slitted to certain widths that have been predetermined so that the proper size of the pipe is created.
Second, the steel enters the mill and is uncoiled and flattened. the steel ribbon is shaped using steel rollers. The ends are sheared and welded together, creating one large, single ribbon of steel.
Third, the forming process begins, meaning that heat and rollers are used to form the steel plate into the shape of a curve, then a U-shape, then a cylinder.
Next, in order to fuse the edges together, heat from an electric charge is applied and the steel is welded longitudinally across its length. These electrical shocks are high frequency, low voltage, and high current. This charge prevents manufacturers from having to use welding filler material in the piping.
Sometimes, a weld flash amongst other imperfections will need to be removed from the top and inside using a special tool.
From there, extra seams are removed mechanically and are normalized with the application of heat. The ERW process of manufacturing pipes often time creates a stronger seam area than pipe created with the fusion weld method. ERW piping has a welded joint in its cross-section.
While the pipes are still hot, minor adjustments are made to them so they are the appropriate size. This helps to ensure that all dimensions are correct, like the outside diameter. Then, the pipes are cut to the required length.
Finally, these pipes can be connected in a variety of ways some of which includes flanged, threaded, socket weld and more.
Of course, minor parts of this process are going to vary from manufacturer to manufacturer. This is how they get an advantage over one another and why some ERW pipes are going to be of higher quality. Some manufacturers check weld integrity multiple times and some promise a 100% satisfaction guarantee. Some other examples of how there can be variance amongst ERW piping is in the smoothness of the surface, the strength, the weight of the walls, and how uniform the pipe is in both quality and dimensions.
Electric Resistance Welding is different from a fusion weld or a continuous weld. That process uses has a ribbon of steel plate heated to a high temperature in a furnace. The ribbon will have the correct wall thickness and width to its proper specifications. After being heated, the ribbon is shaped into a cylinder by rollers and the two sides of the ribbon meet. They are fused together to create a seam.
Seamless pipe doesn’t need any Electric Resistance Welding because it never has seams that need to be joined. It has a solid cylinder of steel that is constantly heated and rotated while the center is hollowed out. The process is similar to removing the center of a tree to create a hollowed log or canoe. The only difference is, with steel the material can be changed when hot, so the big is adjusted to get to the correct thickness.
It is always important to do your research when purchasing piping of any sorts. Part of that research should be done when choosing who to buy steel from, but another part is making sure that the pipe is manufactured in a process that makes sense for your specific project needs. We recommend seeing an engineer in order to get recommendations on what sort of pipe best meets your piping needs.