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Examples, characteristics and causes of defects of steel pipes (ii)

Views:2     Author:Site Editor     Publish Time: 2019-05-03      Origin:Site

Steel pipe with six sides inside


Within the six-party

Reason: the tool size is not accurate: such as the head mandrel is irregular, the perforator head back hole eccentric, will inevitably cause uneven wall thickness. The subsequent sizing process is not reasonable, the reduction rate is too large to form the inside six.


Internal screw

The spiral

Features: the inner surface of steel tube has spiral traces, often appear in the thin-walled tube surface, with uneven feel.


Causes: 1) inherent defects of diagonal rolling process. This defect is more prominent when the technological parameters of the mill are not adjusted properly. 2) unreasonable distribution of deformation amount and excessive wall reduction amount. 3) improper configuration of skew mill roll. 4) serious wear of cross - rolling mandlet.


Steel tube inside the fold

In the fold

Causes: loose center, segregation, shrinkage cavity and high inclusion content of continuous casting billet. Improper rolling process can also form.


Pipe internal straight

The straight

Characteristics: there are linear scratches with certain width and depth on the inner surface of steel pipe.


Causes: 1) low rolling temperature, mandels stick with metal hard objects. 2) graphite contains impurities and so on.


Steel tube stub



Characteristics: irregular scars on the outer surface of steel tube caused by collision.


Causes: produced in the cold zone and hot zone of various collision.


Steel tube green line

The green line


Features: the outer surface of the steel tube shows symmetric or asymmetric linear rolling mark.


Causes: 1) diameter sizing machine hole dislocation or serious wear. 2) unreasonable design of roll pass of sizing machine. 3) roll processing is not good, roll edge chamfering is too small. 4) poor roll assembly, excessive gap, etc.


Steel tube evagination

Fold the outside


Features: spiral laminar folding on the outer surface of the steel tube.


Causes: 1) there are folds or cracks on the surface of the billet. 2) the subcutaneous pores and inclusions of the billet are serious. 3) the surface cleaning of tube billet is not good, or there are ears, wrong side, etc. 4) during the rolling process, the surface of the steel tube is lifted and scratched, and then pressed to the base of the steel tube through rolling, forming outer folding, etc.

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