The resistance of a control rolled and aged steel to hydrogen induced cracking (HIC)‎

Abstract EN

Hydrogen absorbed from environment interacts with lattice defects, precipitates and non-metallic inclusions and alters the mechanical behaviour of steel.

This paper examines the role of microalloy carbide precipitate dispersions in a thermomechanically treated Ti V Nb microalloyed steel to obtain a refined grain structure for use in oil and natural gas transmission pipeslines.

The positive effect of microalloy carbide precipitates of Ti, V and Nb on the resistance to hydrogen embrittlement (HE) of the steel is interpreted in terms of the hydrogen trap theory.

Accordingly, hydrogen partitioned and entrapped by fine dispersions of Ti, Nb, and V carbonitride precipitates is rendered relatively harmless by causing the hydrogen concentration per trap to remain below the critical concentration level required to cause hydrogen-induced cracking (HIC).

Mechanical test, scanning electron microscopy (SEM) and energy dispersive x-ray (EDAX) analytical data are presented.

It is shown that appropriate thermomechanical processes designed in the light of the detailed physical metallurgy of the microalloyed steel markedly improves the hydrogen embrittlement (HE) resistance of the steel investigated.

The control rolled steel aged for a short time (90 minutes) at 600oC possesses excellent resistance to (HIC) and (HE) and stands as an attractive economical option for application in natural gas/oil transmission pipelines.