Bending calculation of seamless black steel pipe

Posted by zora li on March 22nd, 2023

Seamless black steel pipe is a steel pipe made by perforating the whole round steel with no welds on the surface. The bending degree refers to the bending of the steel pipe in the length direction, and the degree of bending is expressed in numbers. The curvature specified in the standard is generally divided into the following two types:

1) Local curvature: Use a one-meter-long ruler to measure the curved part of the steel pipe, and measure its chord height. The unit is mm, which is the local curvature value. The unit is mm/m, and the expression method is 2.5 mm/m. Suitable for measuring the curvature of pipe ends.

2) The total bending degree of the whole length: use a thin rope to tighten the two ends of the pipe, measure the chord height mm of the bending part of the steel pipe, and then convert it into a length percentage in meters, which is the full length bending of the steel pipe in the length direction.

For example: the length of the steel pipe is 10m, and the measured maximum chord height is 30mm, then the bending degree of the whole length of the pipe should be:
0.03/10m*100%=0.3%

Uneven wall thickness of seamless black steel pipe: the wall thickness of the steel pipe cannot be the same everywhere, and there are uneven wall thicknesses in the cross section and longitudinal pipe body. In order to control this unevenness, some steel pipe specifications stipulate the allowable index of uneven wall thickness, which generally stipulates that it should not exceed 80% of the wall thickness tolerance (implemented after negotiation between the supplier and the buyer).

Out of tolerance: The specifications of the seamless pipe exceed the allowable deviation of the national standard. The deviation may be "positive" or "negative", and it is rare that the "positive and negative" deviations are inconsistent in the same batch of steel pipes. There is a phenomenon of unequal outer diameter on the seamless steel pipe section, that is, the outer diameter and the small outer diameter are not necessarily perpendicular to each other, and the difference between the outer diameter and the small outer diameter is called ellipticity (or out of roundness). In order to control the ovality, some seamless steel pipes stipulate the allowable index of ovality, which is generally stipulated as not exceeding 80% of the outer diameter tolerance (implemented after negotiation between the supplier and the buyer).

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