27.13.1. What should be noted when chamfering?

(1) Layering and InclusionsWhen processing the pipe ends, operators should carefully check whether there are any layering or inclusions at the pipe ends. Steel pipes are not allowed to have layering or inclusions extending to the pipe end or bevel face that exceed 6.4mm in transverse dimensions. For pipe ends exceeding 6.4mm, re-cutting is allowed until the layering or inclusions do not exceed 6.4mm.(2) Hard BlocksSteel pipes must not have hard blocks exceeding 50mm in any direction, with hardness values higher than 35HRC (327HBW/345HV10). If present, they may be removed.(3) Bevels and Blunt EdgesUnless the customer has special requirements, steel pipes with wall thickness greater than 3.2mm should be beveled at an angle of 30° to 35°; the blunt edge should be 1.6±0.8mm, measured with respect to the perpendicular line to the pipe's axis at the bevel angle. The pipe end's bevel should not exceed 1.6mm. For GB/T3091 products and SY/T5037 products with pipe diameter D≥813mm, the bevel dimension can be relaxed to 3.0mm.To eliminate inner burrs caused by processing the pipe end, the internal chamfer at the pipe end should not exceed 7°, with measurements based on the centerline of the steel pipe.