Tracking Supervision of Service Performance and Life Assessment of Defective 15Cr1Mo1V Steel Pipeline

Abstract

A large number of inclusion defects were found during the metal supervision process of 15Cr1Mo1V steel main steam pipeline of the Russian-made thermal power unit. In this paper, the tracking supervision research of 15Cr1Mo1V steel pipe elbow with inclusion defects is carried out. The variation law of strength, toughness, metallographic structure and creep rupture strength with inclusion defects at different operating time is studied. Type and composition of inclusions are analysed and creep fatigue crack evaluation of the most serious inclusion defects discovered is performed. The results show that with the increase of service time, the room temperature and high temperature strength of the material gradually decreased, the impact toughness deteriorated, the ductile-brittle transition temperature increased and greater than room temperature, the metallurgical organization aging grade rose from 3 to 4, creep rupture strength decreased, creep aging was increasingly serious, and creep residual life reduced. The main inclusions are plastic MnS、SiO2 and severe inclusion levels up to 3. Longitudinal inclusions are mostly long-chain features, and the ends are sharp but no sharp cracks are found at the sharp ends; the transverse inclusions are granular. Creep fatigue crack evaluation show that there was no obvious growth of material inclusion defects with the increase of service time, it is necessary to strengthen the supervision and inspection of brittle inclusions in the follow-up operation.