The inner surface defects of seamless pipe

Posted by zora li on May 7th, 2024

The inner surface defects of seamless pipe

1. Internal surface defects of seamless pipe:

- Inward folding characteristics: linear or spiral sawtooth defects, caused by tube blank quality, uneven heating, improper adjustment of punching machine parameters, etc.

- Internal scarring: Scarring appears, caused by impurities in graphite lubricant, iron ears in unused pipes, etc.

- Warped skin: small raised skin in the shape of nails. Causes include improper adjustment of punching machine parameters, sticking of steel on the head, accumulation of iron oxide scale, etc.

- Inner straight track: There are linear scratches with a certain width and depth. The causes include metal hard objects stuck to the mandrel, impurities in the graphite, etc.

- Inner edge: There is a linear protrusion with a certain width and depth. The reasons include serious wear of the mandrel and uneven grinding.

- Inner bulge: regular bulging, caused by excessive grinding of continuous rolls, etc.

- Dimples: regular or irregular pits, caused by improper adjustment of continuous rolling and uneven heating of the tube blank.

- Internal threads: There are spiral marks on the inner surface of the steel pipe, which mostly appear on the inner surface of thin-walled pipes. The causes include inherent defects in the cross-rolling process and excessive wall reduction.

2. Judgment: 

-General and casing pipes are allowed to have inner straights with a depth not exceeding 5%, and inner straights with sharp edges should be smoothed.

- Casings and line pipes are allowed to have inner edges with a height not exceeding 8% of the wall thickness. If the height exceeds 8% of the wall thickness, they should be ground and re-cut.

- For steel pipes required for L2 level flaw detection, the inner edge height shall not exceed 5%. Sharp inner edges should be smoothed.

- The negative deviation of the wall thickness is not exceeded, and the concavity where the actual wall thickness is greater than the required minimum value of the wall thickness is allowed to exist. Exceeding dents should be removed.

- The depth of defects in the internal thread of the steel pipe is not greater than 0.3mm and is within a certain tolerance range.