Characteristics and Requirements of ERW Pipes for Steam

ERW (Electric Resistance Welding) is a manufacturing process that uses the thermal effect of high-frequency electric current to melt the edges of steel strip and fuse them together under pressure. ERW pipes offer high production efficiency and low cost, making them a common pipe for transporting medium and low-pressure fluids.

Main Characteristics of ERW Pipes for Steam:

The widespread adoption of ERW pipes for steam stems from the following key advantages:

1. High Production Efficiency and Cost-Effectiveness

The ERW process utilizes continuous forming and welding, resulting in production speeds significantly faster than seamless steel pipe (SMLS) and submerged arc welded pipe (SAW). This results in lower manufacturing costs and offers significant price advantages while meeting application requirements.

2. High Dimensional Accuracy and Excellent Appearance
ERW pipes are manufactured from cold-rolled steel strip or coils, with extremely precise control of outer diameter and wall thickness, and close tolerances. The pipes' smooth inner and outer surfaces are free of scale, resulting in a significantly superior appearance compared to hot-rolled seamless steel pipes.

3. Excellent Weld Quality
Modern high-frequency welding (HFW) technology produces very narrow welds with minimal heat-affected zones. Through in-line heat treatment (normalizing), weld strength can even reach levels comparable to the parent metal. Nondestructive testing ensures weld reliability.

4. Relatively Long Cut Lengths
Due to continuous production, ERW pipe can easily be produced in long cut lengths (e.g., over 12 meters), reducing the number of joints in the piping system and improving overall system integrity and safety.

Strict Requirements for ERW Pipe for Steam:

Since steam transportation involves high temperatures and high pressures, extremely high demands are placed on the safety, sealing, and durability of the pipes. Therefore, ERW pipe for steam must meet a series of stringent standards and specifications.

1. Material Requirements
Steam ERW pipe must be made of steel with excellent high-temperature resistance. Common steel grades include:

ASTM A106 Grade B: The most commonly used carbon steel seamless pipe standard, but high-quality ERW pipe is often produced according to this standard's chemical composition and mechanical property requirements. 

ASTM A53 Grade B: This standard covers both seamless and welded (ERW) steel pipes and is a common choice for low-pressure steam systems.

GB/T 3087: This standard covers low- and medium-pressure boiler pipes in China, suitable for applications with lower steam parameters.

Harsh Environments: High-temperature and high-pressure applications may require alloy pipes, such as ASTM A335 P11/P22, for high-temperature and high-pressure steam.
Deoxidation Method: Killed steel (especially fine-grained killed steel) should be used to ensure uniform microstructure, stable performance, good impact toughness, and weldability. Rimmed steel is strictly prohibited.

2. Manufacturing and Process Requirements

Weld Treatment: This is the most critical requirement. Welds must undergo in-line heat treatment to eliminate internal stresses and microstructural defects introduced during welding, refine the grain size in the weld area, and restore mechanical properties (especially toughness and strength) to those of the parent material.

Non-Destructive Testing (NDT): ERW pipe welds must undergo 100% NDT. 

Online Ultrasonic Testing (UT): Automated scanning of the entire weld length during production to detect internal defects such as lack of fusion, slag inclusions, and porosity.

Eddy Current Testing (ET): Commonly used to detect near-surface defects.

For high-pressure steam pipes, offline ultrasonic testing or X-ray testing (RT) is sometimes required to ensure integrity.

Hydraulic Testing: Every steel pipe undergoes a rigorous hydrostatic test. The test pressure is typically 1.5 times or higher than the specified working pressure, maintained for a specified period of time, to verify its pressure-bearing capacity and leak-tightness.

3. Dimensional and Tolerance Requirements
Outer diameter, wall thickness, ovality, and straightness must be strictly adhered to by relevant standards (such as ASTM A53 and ASME B36.10M). Accurate dimensions are essential for ensuring the quality of subsequent installation and welding.

4. Inspection and Certification Requirements
Third-Party Inspection: For important projects, purchasers typically entrust third-party inspection agencies (such as BV and SGS) to conduct factory audits, production process supervision, and pre-shipment inspections.
Material Certificate: The supplier must provide a complete Material Certificate (MTC) that clearly lists the steel pipe's chemical composition, mechanical property test results, heat treatment status, hydrostatic test values, and NDT results, and must comply with standard requirements.

Selection and Usage Notes:

1. Pressure and Temperature Rating: The correct pipe steel grade and wall thickness (Schedule) must be selected based on the steam design pressure and temperature. Design calculations must always comply with ASME B31.1 "Power Piping" or relevant national standards.

2. Applicable Limits: Although modern ERW technology is advanced, seamless steel pipe remains the preferred choice for extremely high-temperature and high-pressure conditions (such as supercritical and ultra-supercritical power plant main steam piping) because it theoretically eliminates the potential weakness of longitudinal welds. ERW pipe is widely used in medium-, low-, and medium-pressure steam pipelines, gathering and transportation pipelines, and heat exchanger bundles.

3. Installation and Welding: During on-site installation and welding, the welding procedure specifications must be strictly followed. Welders must hold relevant qualifications. Secondary welding or drilling of ERW pipe welds on site is strictly prohibited.

Conclusion:

ERW steam pipe is a technologically mature, cost-effective, and reliable piping product. Its core advantages lie in precise dimensions, smooth surfaces, and high-strength welds that undergo rigorous quality control. As long as the product meets regulatory requirements, it can be safely and reliably used in most industrial and power plant steam distribution systems.

Read more: Carbon Steel ERW Boiler Tube & Air Heater Tube Specification