Differences between Electric Resistance Welded Pipe and Ordinary Welded Pipe

Welding principles and process differences:

1. Electric Resistance Welded Pipe (ERW Pipe)

- Use the resistance heat (temperature up to 1300-1500℃) generated when the current passes through the metal joint to melt the material and form it under pressure without filling metal.

- Process characteristics: high-frequency current (100-800kHz) centralized heating, fast welding speed (up to 20-30 meters/minute), narrow heat-affected zone (about 1-2mm).

- Typical applications: thin-walled pipes such as oil casing and automobile transmission shafts (wall thickness is usually ≤12mm).

2. Ordinary welded pipe (taking arc welded pipe as an example)

- Use electric arc to melt the welding rod or wire and the base material to form a molten pool and then cool it down to connect. Common processes include submerged arc welding (SAW) and manual arc welding (SMAW).
- Process characteristics: large heat input (arc temperature is about 6000℃), wide heat-affected zone (5-10mm), and subsequent heat treatment is required to eliminate stress.
- Typical applications: medium-thick wall pipes such as building structure pipes and water pipes (wall thickness can reach more than 50mm).

Performance and quality comparison:

1. Mechanical properties

- Electric resistance welded pipe: Due to rapid heating and cooling, the weld strength can reach 90%-95% of the parent material (according to the American Petroleum Institute API 5L standard), but the low-temperature toughness is poor.
- Ordinary welded pipe: The weld strength of arc welded pipe is equivalent to that of the parent material, but the impact toughness is better (impact energy ≥27J at -20℃, refer to GB/T 3091-2015).

2. Defect rate and cost

- Electric resistance welded pipe: The defects are mainly "gray spots" (non-metallic inclusions), with an incidence of about 0.5%-1% (industry survey data), but the production efficiency is high and the overall cost is 15%-20% lower.
- Ordinary welded pipes: prone to defects such as pores and slag inclusions (incidence rate 2%-3%), with high labor and energy costs.

Application scenario selection recommendations:

1. Scenarios where resistance welded pipes are preferred

- Thin-walled pipes that require high precision and mass production (such as pipes for household appliances and bicycle frames).

- Occasions where high surface finish is required (resistance welded pipe roughness Ra≤3.2μm).

2. Scenarios where ordinary welded pipes are preferred

- Thick-walled, large-diameter pipelines (such as Φ≥508mm steel pipes for oil pipelines).

- Structural parts that need to withstand dynamic loads (such as bridge trusses) because arc welded pipes have better fatigue performance.

Read more:  Types and uses of welded steel pipe or Carbon steel ERW black steel pipe

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