What Is Electric Resistance Welding
Electric resistance welding (ERW) is a process in which the edges of a steel strip are heated to welding temperature by the resistance heating effect of electric current and then forged together by pressure to form a continuous longitudinal weld. When the weld nugget is formed, it is always surrounded by a plastic ring, so the molten metal is isolated from the air and the metallurgical process is simple and clean.
Advantages of ERW Pipe
Small heat-affected zone: the heating time is short and the heat is concentrated, so deformation and residual stress are small, and correction and heat treatment after welding are usually not required. No filler metal: no welding wire, electrodes, oxygen, acetylene, or hydrogen are needed, so the welding cost is low. High productivity: the process is easily mechanized and automated, with no noise and no harmful gases, and it can be integrated into a continuous production line. Improved working conditions: operators work with automated equipment rather than manual arc welding.
Disadvantages and Limitations
Non-destructive testing limitations: there is a lack of fully reliable online NDT methods for the weld, so quality is verified by destructive testing of process samples and by monitoring technologies. Joint geometry: point and seam welded lap joints increase component weight and create a notch around the weld nugget, resulting in lower tensile and fatigue strength of the joint. Equipment cost: the equipment has high power and a high degree of mechanization, making the initial cost high and maintenance demanding, and high-power single-phase AC welding machines can unbalance the power grid.
Applications
ERW pipe is widely used for structural hollow sections, line pipe for low and medium pressure service, water and gas distribution, and general mechanical tubing. It is available in carbon steel and stainless steel, with common specifications including structural standards and API 5L for line pipe.
Quality Considerations
Modern ERW mills use high-frequency induction or conduction welding with inline heat treatment of the weld zone, eddy current or ultrasonic inspection of the full seam, and hydrostatic testing. These measures reduce the historical concerns about weld quality and expand the acceptable applications of ERW pipe.
Frequently Asked Questions
Q: What is the main advantage of ERW pipe?
A: High productivity and low cost: no filler metal is needed, the heat-affected zone is small, and the process is fully automated for mass production.
Q: What is the main limitation of ERW pipe?
A: The weld is formed without added metal and was historically difficult to inspect online, so quality relies on process control, seam heat treatment, and NDT.
Q: How is the ERW weld inspected?
A> The full weld seam is examined by eddy current or ultrasonic testing, with destructive testing of samples and hydrostatic testing of each pipe.
Q: Is ERW pipe suitable for pressure service?
A: Yes, when manufactured and tested to the applicable standard, ERW pipe is accepted for line pipe and low-to-medium pressure service.
Q: What is the difference between ERW and flash butt welding?
A: ERW heats the strip edges by resistance and forges them together; flash butt welding uses flashing to heat and upset the joint, and must be isolated because of spark splash.
Q: What is the difference between ERW and SAW pipe?
A: ERW uses resistance heating without filler metal and suits thin walls; SAW uses a submerged arc with filler and suits thick walls and large diameters.
For ERW pipe quotations with your required size, grade, and standard, contact our sales team.
