(1) Steel grade and chemical composition. For example, the American standard astm a53, astm a106.
(2) Defects of low magnification structure. The macrostructure defects of the tube billet directly affect the internal quality of the steel tube. In order to improve the physical quality of the tube billet and meet the requirements of the rolled tube for the internal quality of the steel tube, it is stipulated that the defects in the acid leaching macrostructure test piece are allowed to be centered on looseness and shrinkage. For holes, subcutaneous cracks, middle cracks, central cracks and subcutaneous bubbles, the qualification level shall not be greater than 2.0 respectively.
(3) Low-magnification crystal structure. A reasonable thickness ratio of the surface layer fine grain area, columnar crystal area and equiaxed crystal area, especially the ratio of the equiaxed crystal area, is beneficial to control the internal quality of seamless steel pipes. The long axis of the equiaxed crystal area is generally not less than 25% of the nominal diameter, and the qualification level is negotiated by the supplier and the buyer.
(4) Size, shape and weight. The billet is delivered according to the actual weight, and the theoretical weight can also be delivered after negotiation between the supplier and the buyer.
(5) Surface quality. The surface quality of the tube blank determines the surface quality of the steel pipe. The surface of the tube blank is not allowed to have visually visible cracks, inclusions, scars, pores, pinholes, cold skin, joint marks, and scratches, pits, and dents that exceed 1.0mm. Indentation, these defects can be removed by grinding.