Steel pipes are long, hollow tubes that are mostly used to transport goods from one area to another. They are primarily manufactured using two unique production procedures that result in either welded or seamless pipe. Raw steel is initially cast into a more practical beginning form (hot billet or flat strip) in both production procedures. The heated steel billet is then stretched out into a seamless pipe, or the edges of a flat steel strip are forced together and sealed with a weld. This article will go through the many processes used in the production of welded pipes.
Pipe is made using the Electric Resistance Welding (ERW) technique, which involves cold-forming a flat sheet of steel into a cylindrical shape. Then, without the use of welding filler material, current is fed between the two sides of the steel cylinder to heat the steel to the point where the edges are pressed together to form a connection.
For pipe manufacture, many Electric Resistance Welding (ERW) techniques are available. The two most common forms of ERW are:
Welding at High Frequency
Welding with a Rotary Contact Wheel.
Welding at High Frequency
Initially, the ERW manufacturing technique employed low-frequency alternating current to heat the edges. From the 1920s through 1970, this low-frequency method was employed. The low-frequency method was replaced in 1970 by high-frequency ERW technology that generated a higher-quality weld. Low-frequency ERW pipe welds were discovered to be sensitive to selective seam corrosion, hook fractures, and poor seam bonding over time; hence, they are no longer utilized to construct pipe. The high-frequency ERW method is still employed in the pipe manufacturing industry.
High-frequency ERW processes are classified into two categories.
Induction Welding at High Frequency
Contact Welding at High Frequency
In high-frequency induction welding, the weld current is transferred to the material through a work coil in front of the weld spot. The work coil is not in touch with the pipe. Magnetic fields that surround the pipe produce an electrical current in the pipe material. When changing pipe sizes, high-frequency induction welding avoids contact marks and decreases setup time.
In high-frequency contact welding, the weld current is transferred to the material via contacts that ride on the strip. Because the weld power is delivered directly to the pipe, this procedure is more energy efficient than high-frequency induction welding. It is well-suited to large diameter and high wall thickness pipe manufacture because it is more efficient.
In rotary contact wheel welding, the electrical current is transferred through a contact wheel at the weld spot. The contact wheel also applies some of the forge pressure required for welding. AC, DC, and square wave are the three major types of rotary contact wheel welders. Electrical current is transmitted by brush assemblies that engage slip rings attached to a revolving shaft that supports the contact wheels in all three power supplies. The electricity is transferred to the strip edges via these contact wheels.
Rotary contact welding is beneficial in instances where an impeder cannot be accommodated inside the pipe or tube. Small-diameter refrigeration-grade tubing is one example of this. The tube is painted on the ID immediately after the welding process.
An arc is formed between a constantly supplied bare wire electrode and the workpiece during the Submerged Arc Welding (SAW) process. A flux is used in the process to create protective gases and slag, as well as to contribute alloying components to the weld pool. It is not necessary to use shielding gas. Excess flux is recycled via a hopper as the arc advances along the joint line. After welding, any remaining fused slag layers may be simply removed. The arc is generally not visible during welding since it is entirely covered by the flux layer, and heat loss is also quite minimal. This results in a thermal efficiency of up to 60% (compared to 25% for a manual metal arc).