Steel pipe internal stratification

The tube is generally believed that non-metallic inclusions in the steel tube will destroy the continuity and compactness, severe inclusions will lead to appear the steel pipe delamination phenomena. Another thought is hydrogen induced cracking, namely due to hydrogen accumulation caused by metal steel internal gas pressure is too high, the formation of white spots in the round tube, crack extension occurs in the rolling process, and ultimately form a layered defects. In addition, the stress exceeds the strength of two rolls of plastic rotary piercing uneven deformation can also cause delamination.

The control measures of steel pipe internal stratification are:

1, Improved plastic toughness of tube billet

Improve the cleanliness of molten steel, reducing harmful inclusions; increase the proportion of the slab crystal axis, to reduce the center segregation and center porosity; using reasonable cooling system to avoid cracks appeared in the interior slab; billet or rolling slab to be taken offline slow cooling process, reducing internal stress, thus ensuring the microstructure and mechanical properties of steel billet and finished products meet the technical standards.

2, Reasonable control heating temperature

By measuring thermoplastic curve to choose the best heating temperature. Also note that there is enough heating tube holding time, to reduce the pipe plastic deformation resistance and improve toughness.

3, Reduce the roll speed

Speedis a key parameter roll piercing process, in the roll speed from low to high variations in the process, there is a critical stratification began the roll speed. At lower roll speed, easy to form a tube cavity; higher roll speed, and capillary tube formation of layered defects easily. In order to eliminate delamination defects and capillary tube, roll speed should be reduced to the critical stratification began following the roll speed.