Common defects of welded pipes

If the defects such as the chemical composition and mechanical properties of the welded steel pipe blank that need to be known by certain testing methods are collectively referred to as invisible defects; then, those defects that can be seen only by vision may be called tube blank dominant defects. Here are two of them.

scratches

Scratches refer to the scratch marks on the surface of the tube blank. The characteristics of scratches are mostly vertical and relatively fixed, and there are certain rules to follow.

Causes of scratches:

(1) During cold rolling, hard foreign matter entered the tension plate of the rolling mill and scratched the surface of the billet.

(2) There are hard foreign objects in the splint of the slitting tension station intruding and scratching.

(3) When the welded pipe is stored, the rotation of the feeding roller is not flexible and scratches the surface of the board.

(4) Scratches on the outer ring of the billet are mainly caused by accidental rubbing during storage, hoisting and transportation.

The effect of scratches on the quality of welded pipes:

The impact on the quality of the welded pipe is similar to that of the pitting.

Burrs and edge warping

The tube blank burr refers to the residual on both sides of the trimmed tube blank, which is higher than the plane, and is touched horizontally by hand (for safety reasons, it must be touched horizontally), it is not smooth, and it feels like it is on the blade.

Edge warping is the part where the edges on both sides of the tube blank plane are warped relative to the plane.

The edge burr and the edge warping of the tube blank are twin brothers. Usually, the edge burr is large, the edge warping is serious; on the contrary, if the edge warping is serious, the edge burr must be large;The two coexist with the slitting tube blank, but the degree is different. Slight edge burrs and edge warping can be partially corrected by forming rolls, but warping cannot be eliminated.

Causes of burrs and edge warping:

(1) The slitting blade of slitting is not sharp.

(2) The precision of the knife shaft of the slitting machine is poor, or there are impurities on the plane of the spacer, which causes the plane of the slitting knife to swing on the knife shaft, which affects the side clearance and produces periodic burrs on the edge of the tube blank.

(3) The gap between the upper and lower edges of the slitting blade is too large.

The effect of burrs and edge warping on the quality of welded pipes:

(1) Slight tube blank burrs and edge warping have little effect on thick-walled and standard-walled tubes.For some pipes that require small and extra-small burrs, the purpose can also be achieved by feeding the pipe blank.

(2) When the edge warping is serious, a "corner joint" of the weld will be formed, that is, the outer edge corner joint will appear when the A side is rolled on the outside.When the A side is rolled into the inside, there will be an inner edge fillet, and the two edge butt forms are not desired by the welding process.

(3) It is difficult to remove the outer burr of the thin-walled tube. In the production of thin-walled tubes, tube blanks with large edge burrs and warped edges should be avoided as much as possible.

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