Comparison of SSAW pipe and ERW pipe technical characteristics

Metallurgical Properties

SSAW Pipes: Made from hot-rolled coils, which have advantages in producing high-quality pipeline steel. The hot-rolled strip mill’s process, including a water cooling system, allows for low alloy composition, enhancing weldability and producing higher strength and toughness. The rolling direction in SSAW pipes (determined by the helix angle) improves crack resistance compared to ERW pipes.

ERW Pipes: Made from steel plates, with the rolling direction perpendicular to the pipe’s axis, making them less crack-resistant than SSAW pipes.

Welding Process

SSAW and ERW Pipes: Both use the same welding method, but ERW pipes have more T-shaped welds, increasing the probability of defects. The T-shaped welds also experience higher stress and are more prone to cracks.

Submerged Arc Welding: Requires an arc starting and stopping point for each weld, a condition not always met in ERW pipes, potentially leading to more welding defects.

Strength Characteristics

Internal Pressure: SSAW pipes experience two main stresses: radial (δY) and axial (δX). The resultant stress at the weld (δ) is calculated as δ=δY(l/4sin2α+cos2α)1/2, where α is the helix angle. The helix angle of 50-75 degrees in SSAW pipes results in composite stress at the weld being 60-85% of the principal stress in ERW pipes. Consequently, SSAW pipes can have thinner walls under the same working pressure.

Blasting Safety: SSAW pipes are safer as the stress on the weld is lower, reducing the risk of crack propagation.

Stress Distribution: Radial stress is the highest stress, with straight seams bearing the most load, circumferential welds the least, and spiral seams in between.

Static Pressure Burst Strength

Yield and Burst Pressure: SSAW pipes have similar yield and burst pressures to ERW pipes. However, SSAW pipes show better plastic deformation during blasting, indicating higher toughness.

Toughness and Fatigue Strength

Large Diameter and High Strength: SSAW pipes have higher impact toughness and fatigue strength, making them suitable for large-diameter and high-strength applications.

Fatigue Resistance: SSAW pipes exhibit fatigue strength comparable to seamless and resistance welded pipes, superior to general submerged arc welded pipes.

Field Solderability

Material and Fit Tolerance: SSAW pipes, produced in a continuous process, have better weld quality and geometric consistency compared to the segmented production process of ERW pipes.

On-site Welding: SSAW pipes have better nozzle ellipticity and end face verticality, ensuring accurate alignment during on-site welding.

Influence on Flow Characteristics

Pressure Drop: Determined by pipe length, fluid viscosity, velocity, resistance coefficient, and inner diameter. The roughness of the inner wall surface significantly impacts fluid resistance, more so than local bulges like welds.

Production and Management

High Efficiency: One SSAW pipe unit can match the production capacity of 5-8 ERW pipe units. However, coordinating multiple units to meet the same quality standards poses management challenges.

Quality Supervision: Multi-head production increases the complexity of management, quality control, and coordination, leading to potential issues in planning, inspection, and delivery.

Quality Assurance

Inspection Items: Include dimensions, wall thickness, ellipticity, curvature, pipe end verticality, weld reinforcement, misalignment, surface quality, delamination, inclusions, and weld defects.

Continuous Inspection: SSAW units typically employ continuous inspection methods, ensuring stable welding quality and grade. In contrast, continuous inspection is challenging for ERW pipes, increasing the risk of hidden defects and affecting long-term reliability.