Steel Pipe Practitioners Need To Master The Concept Of Steel Pipe Defect Terminology

1 roundness: round cross-section of the rolled material, such as round steel and round steel pipe cross-section, the diameter in all directions is not equal;

2 shape is not correct: rolled material cross-section geometry is skewed, uneven. such as hexagonal steel six sides are not equal, angle steel top angle is large, section steel twisted;

3 uneven thickness: steel plate (or steel strip) the thickness of each part of the plate is not the same, some of the two sides of the thick and thin in the middle, some of the side of the thin and thick in the middle, there are also head and tail difference exceeds the provisions;

4 curvature: rolled parts in the length or width direction is not straight, curved;

5 sickle bend: steel plate (or steel strip) length direction in the horizontal plane to one side;

6 scoop curvature: steel plate (or steel strip) in the length and width direction at the same time the phenomenon of undulating waves, making it a "scoop" or "boat-shaped";

7 torsion: strip rolling along the longitudinal axis twisted into a spiral;

8 de-square, de-rectangular square: rectangular cross-section of the material is not equal to the sides or the diagonal of the cross-section is not equal;

9 pull marks (scratches): a straight line groove, the naked eye can see the bottom of the groove is distributed in the local or full length of the steel;

10 cracks: generally linear, sometimes y-shaped, mostly in the same direction as the direction of drawing, but there are other directions, the general opening for the acute angle;

11 heavy skin (scarring): the surface of the tongue or fish scales in the form of warped flakes. one is connected to the body of steel, and folded to the surface is not easy to fall off; another is not connected to the body of steel, but bonded to the surface is easy to fall off;

12 folding: steel surface partial overlap, there is a clear folding pattern;

13 rust: surface generated rust, its color from apricot yellow to black-red, rust removal, serious rust pockmarks;

14 hairline: surface hairline is a very shallow depth, very small width of hair-like fine lines, generally extended along the rolling direction to form fine grain strands;

15 delamination: steel cross-section has a localized obvious metal structure separation, serious cases are divided into 2 ~ 3 layers, layers and layers between inclusions visible to the naked eye;

16 bubbles: the surface of the irregular distribution of rounded large and small convex package, its outer edge is relatively rounded. most of them are bulging, and some of them are not bulging and the surface is bright after acid washing and leveling, and their shear section is layered;

17 pitting (pitting): the surface shows localized or continuous patches of rough surface, distributed in different shapes and sizes of pits, and in severe cases, similar to orange peel-like, larger and deeper than the pitting pitting;

18 oxidation color: steel plate (or steel strip) after annealing on the surface of light yellow, dark brown, light blue, dark blue or bright gray;

19 roll mark: the surface has a band or sheet of periodic roll marks, its embossed parts of the brighter, and no obvious convexity and concavity feeling;

20 loose: a manifestation of the steel is not dense. slice after acid erosion, expanded into many cavities, according to its distribution can be divided into: general sparsity, center sparsity;

21 segregation: the phenomenon of uneven distribution of chemical composition and non-metallic inclusions in various parts of the steel. according to its manifestation can be divided into: dendritic, box-shaped, point-like segregation and anti-segregation;

22 shrinkage holes: residual in the center of the transverse acid immersion test piece, showing irregular voids or cracks. foreign impurities often remain in the voids or cracks;

23 non-metallic inclusions: in the transverse acid test piece to see some of the non-metallic luster, gray, beige and dark gray and other colors, the department of steel residual oxides, sulfides, silicates, etc.;

24 metal inclusions: in the transverse low-power specimen to see some of the metal luster and the base metal apparently different metal salts;

25 overcooking: observation of the microstructure after erosion, often in the network oxide around the base metal can be seen on the decarburization organization, other metals such as copper and its alloys have copper oxide along the grain boundaries in the form of a network or point to the internal extension of the specimen;

26 white point: it is a kind of internal rupture of steel. in the longitudinal fracture of the steel piece is a round or oval silver-white spots, after grinding and acid etching after the transverse section, it is manifested as a slender hairline crack, sometimes radial distribution, and sometimes parallel to the direction of deformation or irregularly distributed;

27 coarse grains: a strong metallic luster on the fracture of the acid-etched specimen;

28 decarburization: the surface carbon of steel is lower than the inner layer of carbon phenomenon known as decarburization. full decarburization layer refers to the surface of the steel due to decarburization and present all the ferritic organization part; part of the decarburization is the full decarburization layer to the steel after the carbon content has not been reduced at the organization.