How to Choose Welded Pipe: ERW, LSAW, or SSAW?

ERW, LSAW, and SSAW are three of the most common welded pipe processes, differing significantly in raw materials, forming methods, weld morphology, specification range, and applicable scenarios. This article outlines the core characteristics of these three processes to help you make the choice based on your project needs.

1. ERW Pipe: An Economical Choice for Small and Medium Diameters

ERW (Electric Resistance Welding) pipe is produced using hot-rolled wide strip steel coils as raw material, through continuous cold bending, high-frequency resistance welding, heat treatment, sizing, and straightening processes. The weld is a straight seam, short, and compared to spiral welded pipe, it offers advantages such as higher dimensional accuracy, uniform wall thickness, and better surface quality.

Key Features:

Specifications: Outer diameter typically not exceeding 24 inches (approximately 610mm), wall thickness relatively thin, generally not exceeding 22mm.

Cost Advantages: High production efficiency, high raw material utilization, and lower overall cost.
Precision Advantages: Dimensional accuracy and wall thickness uniformity superior to SSAW.

Limitations: Can only produce small to medium diameter thin-walled pipes; cannot produce large diameter thick-walled products. Defects such as gray spots, lack of fusion, and grooved corrosion are prone to occur at the weld seam.

Typical Applications: Medium to low pressure scenarios such as urban gas transmission, crude oil and refined oil transmission, and building structural pipes.

2. LSAW Pipe: The Mainstay of Large-Diameter High-Pressure Pipelines

LSAW (Longitudinal Submerged Arc Welding) pipe uses a single medium-thick steel plate as raw material, pressed into a pipe blank in a mold or forming machine, and produced using a double-sided submerged arc welding method. Common forming methods include UOE and JCOE.

Key Features:

Specification Range: Diameters from 16 to 60 inches (approximately 406-1524 mm), wall thickness up to 40 mm and above.
Quality Advantages: Excellent weld toughness, plasticity, uniformity, and density; features large diameter, thick wall, high pressure resistance, low temperature resistance, and strong corrosion resistance.
Highest Reliability: Weld coefficient up to 1.0, with strength equivalent to the base material.

Unique Status: According to API standards, straight seam submerged arc welded pipe is the only designated applicable pipe type for large oil and gas pipelines passing through Class 1 and 2 areas such as high-altitude cold regions, seabeds, and densely populated urban areas.

Typical Applications: Long-distance high-pressure oil and gas trunk lines, submarine pipelines, pipelines in high-altitude cold regions, urban high-pressure ring networks, and other harsh working conditions.

3. SSAW Pipe: An Economical and Flexible Solution for Ultra-Large Diameters

SSAW (Spiral submerged arc welding) pipe refers to pipe formed by spiral submerged arc welding. When the strip steel is coiled, the direction of advance is at a forming angle to the centerline of the formed pipe. Welding occurs simultaneously with forming, resulting in a spiral weld with a diameter of -2-8.

Key Features:
Specification Range: Diameters up to 100 inches (approximately 2500 mm) and above, wall thickness up to 29 mm;
Flexibility Advantage: Multiple diameter pipes can be produced from the same strip steel, offering a wide range of raw material adaptability. Welds can avoid principal stress, resulting in better stress distribution;
Cost Advantage: High production efficiency and relatively low equipment investment.

Limitations: Relatively poor geometric dimensions, long weld length; prone to welding defects such as cracks, porosity, slag inclusions, and weld misalignment; welding stress is tensile; according to general oil and gas long-distance pipeline design specifications, spiral submerged arc welded pipes are typically only suitable for Class 3 and Class 4 areas.

Improvement Directions:
Overseas, the raw material has been changed to steel plate, separating forming and welding. Through pre-welding, precision welding, and post-weld cold expansion, the weld quality approaches that of UOE pipes. However, this technology is not yet available in China, and domestic pipelines are currently still produced using traditional processes.

Typical Applications: Low-pressure fluid transportation (water, natural gas), large-scale water transmission projects, large-diameter pile foundations, municipal infrastructure construction.

Further Reading: ERW Pipe vs. Seamless Pipe: Cost & Selection Guide

Article source: https://article-realm.com/article/Business/83759-Strength-Dimensions-and-Applications-of-N80-Oil-Casing.html