The Pressure Resistance of Spiral Welded Steel Pipes

Spiral welded steel pipes are made by bending steel strips or plates into shapes like circles or squares and then welding them together, resulting in pipes with a seam on the surface. Depending on the welding method, these pipes can be categorized into various types such as arc welded pipes, HFW pipes, gas welded pipes, furnace welded pipes. Based on the seam's shape, they can be classified as straight seam welded pipe or spiral welded pipes.

Straight seam welded pipes are typically used for high-pressure oil and gas transportation.

Spiral welded pipes find their application in oil and gas transportation, pipe piles, and bridge piers.

Compared to seamless steel pipes, welded steel pipes are cost-effective and have higher production efficiency.

Strength Characteristics of Steel Pipes

When a steel pipe is subjected to internal pressure, it experiences two main types of stress on its wall: radial stress (δY) and axial stress (δX). The composite stress at the weld seam (δ) can be expressed as: δ=δY(l/4sin2α+cos2α)1/2

where α is the spiral angle of the weld seam.

For spiral welded pipes, the spiral angle of the weld seam generally ranges from 50 to 75 degrees. As a result, the composite stress at the spiral weld seam is about 60-85% of the main stress at a straight seam weld. This allows the wall thickness of a spiral welded pipe to be reduced compared to a straight seam welded pipe of the same diameter and working pressure.

Advantages of Spiral Welded Pipes

From the characteristics described, several advantages of spiral welded pipes over straight seam welded pipes can be identified:

Higher Safety: In the event of a rupture, the fracture typically does not originate at the spiral weld seam due to the lower normal and composite stresses at this point, making spiral welded pipes safer than straight seam welded pipes.

Lower Risk of Defect Propagation: If defects parallel to the spiral weld seam exist nearby, the lower stress at the spiral weld seam reduces the risk of defect propagation compared to straight seam welds.

Load Distribution: Radial stress is the maximum stress present in the steel pipe. When the weld seam aligns with the direction of this radial stress, it bears the greatest load. Thus:

1. Straight seams endure the highest load.

2. Circumferential seams endure the least.

3. Spiral seams have a load-bearing capacity between the two.

These attributes underscore the robustness and reliability of spiral welded pipes in various industrial applications.