Forming angle formula of spiral welded pipe

The forming angle of a spiral welded pipe is a crucial parameter. It refers to the acute angle between the centerline of the strip steel or coiled plate and the axis of the formed spiral welded pipe. The formula for calculating the forming angle (α) is as follows:

cos⁡(α)=BπD\cos(\alpha) = \frac{B}{\pi D}cos(α)=πDB

where BBB is the thickness of the strip or coil, and DDD is the middle diameter of the steel pipe (outer diameter minus inner diameter).

The selection of the forming angle directly impacts the raw material usage, product quality, and production efficiency of the spiral welded pipe.

Strength Characteristics Comparison: Spiral vs. Straight Seam Welded Pipe

When a pipe is subjected to internal pressure, it experiences two main stresses on the pipe wall: radial stress (δY) and axial stress (δX).

The resultant stress at the weld is given by:

δ=δY(14sin⁡2α+cos⁡2α)1/2\delta = \delta_Y \left( \frac{1}{4 \sin^2 \alpha} + \cos^2 \alpha \right)^{1/2}δ=δY(4sin2α1+cos2α)1/2

where α is the helix angle of the weld in a spiral welded pipe. Typically, the helix angle ranges from 50 to 75 degrees, making the composite stress at the spiral weld 60-85% of the principal stress in a straight seam welded pipe. Therefore, under the same working pressure, the wall thickness of a spiral welded pipe can be thinner than that of a straight seam welded pipe of the same diameter.

Advantages of Submerged Arc Welding Straight Seam Steel Pipe

- Enhanced Mechanical Properties:

Submerged arc welding can refine the grain structure of the steel and unify the microstructure, resulting in a denser steel structure with improved mechanical properties.

This process mainly enhances properties in the rolling direction, reducing the anisotropy of the straight seam steel pipe.

- Defect Elimination:

The process can weld out bubbles, cracks, and looseness formed during the casting of steel ingots under high temperature and pressure, leading to a more robust and reliable weld.

By understanding and optimizing these parameters and processes, manufacturers can improve the efficiency, quality, and performance of spiral welded pipes.