What are the possible defects in the production process of GB/T699 10# high-quality carbon steel pipe?

GB 10 GB/T 699 Chemical

Element	Min	Max	Similar
C	0.0700	0.1300	-
Si	0.1700	0.3700	-
Mn	0.3500	0.6500	-
P	-	0.0350	-
S	-	0.0350	-
Cr	-	0.1500	-
Ni	-	0.3000	-
Cu	-	0.2500	-

GB 10 GB/T 699 Mechanical

Yield Rp0.2 (MPa)	Tensile Rm (MPa)	Impact KV/Ku (J)	Elongation A (%)	Reduction in cross section on fracture Z (%)	As-Heat-Treated Condition	Brinell hardness (HBW)
889 (≥)	873 (≥)	34	32	22	Solution and Aging, Annealing, Ausaging, Q+T,etc	234

Defects that may occur in the production process of 10# pipe

Name	Structural Seamless steel pipe description
Roundness	Rolled products of circular cross-section, such as cross-sections of round steel and circular structural steel pipes, have different diameters in all directions
Incorrect shape	The cross-sectional geometry of the rolled product is skewed and uneven. For example, the six sides of the hexagonal steel are not equal, the top angle of the angle steel is large, and the profile steel is twisted, etc.
Uneven thickness	The thickness of each part of the steel plate (or steel strip) is different, some are thick on both sides and thin in the middle, some are thin on the edge and thick in the middle, and some have a head-to-tail difference exceeding the specification
Curvature	The rolling stock is not straight in the length or width direction, and is curved
Sickle bend	The length direction of the steel plate (or steel strip) is bent to one side in the horizontal plane
Scoop curvature	The steel plate (or steel strip) has undulating waves in the length and width directions at the same time, making it a "scoop-shaped" or "boat-shaped"
Twist	Rolled bars twisted into a helix along the longitudinal axis
Out of square	The material on the opposite sides of the square and rectangular sections is unequal or the diagonals of the section are unequal
Scratch	In the shape of a straight groove, the bottom of the groove can be seen to be distributed in part or the whole length of the structural tube with the naked eye.
Crack	Generally linear, sometimes Y-shaped, mostly consistent with the drawing direction, but there are other directions, generally the opening is an acute angle
Scarring	Lifted sheets with tongue-like or fish scales on the surface: one is connected to the body of steel, and is folded to the surface and is not easy to fall off; the other is not connected to the body of steel, but it is easy to fall off when bonded to the surface
Fold	The surface of the structural tube partially overlaps with obvious fold lines
Rust	The rust generated on the surface, its color is from apricot yellow to black red, after rust removal, there are serious rust pitting
Texture	Surface hair lines are hair-like fine lines with very shallow depth and extremely small width, which generally extend along the rolling direction to form fine lines.
Layered	There is local obvious metal structure separation on the section of the structural pipe, and in severe cases, it is divided into 2 to 3 layers, and there are visible inclusions between the layers.
Bubble	The surface is irregularly distributed in the shape of a circular convex hull, large and small, and its outer edge is relatively smooth. Most of them are bulging, and some are not bulging but the surface is bright after pickling and smoothing, and the shear section is delaminated.
Pockmarks	The surface presents a local or continuous rough surface, with pits of different shapes and sizes distributed, and in severe cases, there are pockmarks similar to orange peel, larger and deeper than pockmarks
Oxidized color	After annealing, the steel sheet (or steel strip) appears light yellow, dark brown, light blue, dark blue or bright gray on the surface
Roll printing	The surface has band-like or sheet-like periodic roll marks, the imprinted parts are bright, and there is no obvious convex and concave feeling
Loose	The performance of the incompactness of the structural tube. After the slice is eroded by acid, it expands into many caves, which can be divided according to their distribution: generally loose, loose in the center
Segregation	The phenomenon of uneven distribution of chemical composition and non-metallic inclusions in various parts of the structural pipe. According to its form, it can be divided into: dendritic, box-shaped, point-like segregation and reverse segregation, etc.
Shrinkage crater residue	There are irregular voids or cracks in the center of the lateral acid leaching test piece. Foreign impurities often remain in voids or cracks
Non-metallic inclusions	Some non-metallic luster is seen on the lateral acid test piece, which is gray-white, beige and dark gray, and the residual oxides, sulfides, silicates, etc. in the steel are
Metal inclusions	Some metal salts with metallic luster obviously different from the base metal were seen on the transverse low magnification test piece
Burnt	When observing the eroded microstructure, the decarburized structure can often be seen on the base metal around the network oxide. Other metals such as copper and its alloys have copper oxide in the form of network or point along the grain boundary. internal extension
White dot	It is a type of internal rupture of a structural tube. Circular or oval silver-white spots on the longitudinal fracture of the structural tube, on the transverse section after polishing and acid etching, appear as slender cracks, sometimes radially distributed, sometimes parallel to the Deformation direction or random distribution
Coarse grains	The acid leaching test piece has strong metallic luster on the fracture
Decarbonization	The phenomenon that the carbon content of the surface layer of the structural tube is lower than that of the inner layer is called decarburization. The full decarburization layer means that the surface of the structural pipe is completely ferrite due to decarburization; the partial decarburization refers to the structure where the carbon content of the steel is not reduced after the full decarburization layer.

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