PRIME STEEL PIPE: electric resistance welding

Showing posts with label electric resistance welding. Show all posts

2017/07/26

Low-frequency Electric Resistance Welding

Low-frequency electric resistance welding (LF - ERW), is an obsolete method that was used to weld seams in oil and gas pipelines. It was phased out in the 1970s but as of 2015 some pipelines built with this method remained in service.

Electric resistance welded pipe (ERW steel pipe) is manufactured by cold-forming a sheet of steel into a cylindrical shape. Current is then passed between the two edges of the steel to heat the steel to a point at which the edges are forced together to form a bond without the use of welding filler material. Initially this manufacturing process used low frequency A.C. current to heat the edges. Over time, the welds of low frequency ERW pipe was found to be susceptible to selective seam corrosion, hook cracks, and inadequate bonding of the seams, so low frequency ERW is no longer used to manufacture pipe. This low frequency process was used from the 1920s until 1970. In 1970, the low frequency process was superseded by a high frequency ERW process which produced a higher quality weld. So the high frequency process is still being used to manufacture pipe for use in new pipeline construction. In the production of ERW steel pipe manufactured by Prime Steel Pipe, high-frequency ERW process is widely used, so that we can guarantee the quality of welding seam and produce high quality ERW steel pipe.

2017/07/03

The Types of Electric Resistance Welding

We knew what is electric resistance welding (ERW) previously, next, Prime Steel Pipe will continue to share the types of Electric Resistance Welding. We will discuss high-frequency ERW (contact and induction) and rotary wheel contact welding (AC, DC, and square wave). And we will share the differences among the processes, as well as the power supplies and weld rolls.

All ERW processes have one thing in common–all of them produce a forged weld, although each process has different characteristics. Several electric resistance welding (ERW) processes are available for ERW steel pipe production. The two main types of ERW are high-frequency (HF) and rotary contact wheel.

High-frequency (HF) Welding

The two main aspects of HF welding are processes and power supplies. The two HF welding processes are HF contact and HF induction. In both processes, the equipment that provides the electrical current is independent from the equipment that supplies the forge pressure. Also, both HF methods can employ impeders, which are soft magnetic components located inside the tube that help to focus the weld current in the strip edges. In the case of HF induction welding, the weld current is transmitted to the material through a work coil in front of the weld point. The work coil does not contact the tube--the electrical current is induced into the material through magnetic fields that surround the tube. HF induction welding eliminates contact marks and reduces the setup required when changing tube size. It also requires less maintenance than contact welding. HF contact welding transfers weld current to the material through contacts that ride on the strip. The weld power is applied directly to the tube, which makes this process more electrically efficient than HF induction welding. Because it is more efficient, it is well-suited to heavy-wall and large-diameter tube production. HF welding machines also are classified by how they generate power. The two types are vacuum tube and solid-state. The vacuum tube type is the traditional power supply.

Rotary Contact Wheel Welding

In rotary contact wheel welding, the electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies some of the forge pressure necessary for the welding process. The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges.