There is a phenomenon of unequal outer diameter on the cross section of the stainless seamless steel pipe, that is, there is a maximum outer diameter and a minimum outer diameter that are not necessarily perpendicular to each other, then the difference between the maximum outer diameter and the minimum outer diameter is the ovality (or out of roundness). In order to control the ovality, some stainless seamless steel pipe standards stipulate the allowable index of ovality, which is generally specified as not exceeding 80% of the outer diameter tolerance (executed after negotiation between the supplier and the buyer).

The formula for calculating the ovality of stainless seamless steel pipe is:

Ovality = (maximum outer diameter - minimum outer diameter) / nominal outer diameter * 100%

Influence of ovality There is a large uneven deformation on the cross section of the tube blank during the perforation process. The greater the ovality, the greater the uneven deformation. According to the law of constant volume, the larger the lateral deformation is, the smaller the longitudinal deformation will be, which will lead to the increase of the transverse tensile stress, shear stress and repeated stress in the center of the tube blank, which will aggravate the formation trend of the cavity.

The tools used for the inspection of the outer diameter and ovality of stainless seamless steel pipes are mainly calipers and vernier calipers. During inspection, use qualified calipers or vernier rulers to measure the outer diameter of stainless seamless steel pipes one by one. When measuring, the caliper or vernier caliper should be perpendicular to the axis of the stainless seamless steel pipe, and the stainless seamless steel pipe should be slowly rotated to measure the large and small points of the section where the stainless seamless steel pipe is located. Hours should be marked. For stainless seamless steel pipes that need to be checked for pipe end ovality, ring gauges are generally used to check. At present, automatic caliper devices can also be used to check the outer diameter of stainless seamless steel pipes.