Welded pipe defects-analysis of opinions on pipe surface scars

Welded pipe defects-analysis of opinions on pipe surface scars

Scratches on the pipe surface are common defects of welded pipes, with specific manifestations such as crushing, indentation and scratching.

1. Crush: refers to the damage of the roll pass to the surface of the tube blank. There are many types of crush, but the causes are nothing more than the following aspects:

a. The bottom line of the pass of a pair of rolls is adjusted higher than the bottom line of the rolling; the whole rolling line produces uneven ups and downs;

b. The vertical roll is too tight.

c. Vertical roll has an elevation angle.

d. The new hole pattern may be that the edge chamfer of the hole pattern is too small or the chamfer angle does not meet the requirements.

e. The high-strength blank tube has large springback and large deformation resistance, and the edge of the hole pattern is easy to "bite" the tube blank.

f. The flat roll is too low, causing the tube blank to be crushed by the lower edge of the vertical roll pass.

g. The vertical roll deviates from the rolling center line.

2. Indentation and Dark Line:

Indentation and dark lines are the products of crushing, and the formation mechanism is roughly the same, but the performance is more concealed, it is not obvious without careful observation, and the hand feel is not obvious, but they all have an impact on the surface quality of the welded pipe.

3.Scratch:

It mainly refers to the damage to the running tube blank caused by the rolls that are not moving or the relative moving speed difference is large, and the characteristic is related to the speed difference. The way to solve the problem can start from two aspects of hole type and adjustment:

a. From the perspective of hole design, without affecting the overall deformation effect, boldly removing the hole pattern is not only harmless to the molding, but also can permanently prevent the troubles of scratches.

b. From the adjustment point of view, according to the location of the scratches, lower the vertical roll appropriately and relax the flat roll. If there is an indentation on one side of the tube blank after the flat roll is discharged, the vertical roll rolling center line before the flat roll should be corrected.

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