EFFECT OF LOCAL PLASTIC STRAINS ON THE PHYSICOMECHANICAL PROPERTIES OF THE MATERIAL AND THE STRESS STATE OF A PIPELINE

摘要

We present the results of investigation of the physicomechanical properties of plastically deformed 17G1S pipe steel after long-term operation. We have studied the susceptibility to hydrogen-induced cracking, corrosion rate, and the influence of hydrogen-sulfide media on the mechanical characteristics and distribution of microhardness over the thickness of the pipe. It is shown that, for 1 % strains, the mi-crohardness of steel increases by 0.39-0.56 GPa. For 3% strains, the increase in microhardness is less pronounced. The hydrogen-sulfide NACE medium insignificantly affects the strength characteristics (σ_(02) and σ_u) but substantially decreases the plasticity characteristics (δ and ψ). Under the influence of hydrogen-sulfide media, the time to fracture of specimens made of both deformed and deformation-free pipe steel noticeably decreases. It is shown that local plastic strains in the pipe significantly affect its stress-strain stale and the formation of plastically deformed zones leads to stress concentration which is especially pronounced on the contours of indents.