In the cross-section of straight seam steel pipes, there may be inconsistencies in the outer diameter, where the maximum and minimum outer diameters are not necessarily perpendicular. Ellipticity (or out-of-roundness) is defined as the difference between the maximum and minimum outer diameters. To control ellipticity, some steel pipe standards specify that ellipticity should not exceed 80% of the outer diameter tolerance.

straight seam steel pipes exhibit curvature in the lengthwise direction, with the degree of curvature expressed in terms of bending. The standard specifications for bending generally fall into two categories:

1. **Local Bending**: Local bending is determined by measuring the chord height (in mm) at the point of maximum curvature using a one-meter long straight edge, with bending expressed in units of mm/m, for example, 2.5mm/m. This method is also applicable for determining bending at the pipe ends.

2. **Total Bending Along the Entire Length**: Total bending is calculated by pulling a taut string from both ends of the steel pipe, measuring the chord height (in mm) at the point of maximum curvature, and then converting it to a length percentage (in meters), representing the total bending along the length of the pipe.

To ensure the quality and performance of straight seam steel pipes, it is crucial to monitor and adhere to the ellipticity and bending specifications outlined in the relevant industry standards.

Remember, when it comes to straight seam steel pipes, precision in ellipticity and bending is key to ensuring structural integrity and optimal performance.