Effect of Hydrogen Concentration in Metal on Residual Durability of Defected Pipelines

Abstract

This study is devoted to the determination of the effect of hydrogen concentration in metal C_H on the residual durability N_f of defected pipelines. Three different cases of defected pipes were considered, namely: pipe with longitudinal semi-elliptical crack at outer surface; pipe with longitudinal semi-elliptical crack at inner surface and pipe with circumferential semi-elliptical crack at inner surface. It has been shown that the presence of the crack-like defects in the pipelines is very dangerous from the point of view of their further reliable operation. This danger significantly increases with the increase of the hydrogen concentration in the metal. The increase of the danger of crack-like defects in the pipes may be expressed by the sequence: longitudinal semi-elliptical crack at outer surface – longitudinal semi-elliptical crack at inner surface – circumferential semi-elliptical crack at inner surface. The residual durability of defected pipe N_f was chosen as the basic parameter for the assessment of its further serviceability. Thus, all defects detected in the pipeline after inspection can be compared with received data and on this base the expert conclusion for the evaluation of the potential risk of each defect can be made.