Degradation of microstructure and properties of an AISI 316L steel pipe after more than 100,000 hours usage at 640°C in a petrochemical industry

AISI 316L austenitic stainless steel is one of the most widely used in its steel class, especially at high temperature. In this work, samples for analysis were taken from a pipe of AISI 316L with a nominal 200 mm external diameter and 15 mm thick exposed for about 100,700 hours at 640°C with an internal pressure of 4.5 MPa in a reactor of a petrochemical plant. Modifications in the microstructure, mechanical properties and corrosion resistance were investigated and the most significant results are presented. Results show the precipitation of intermetallic phases, mainly sigma phase at grain boundaries and inside the grains. Precipitation caused increased hardness, yield strength and ultimate tensile strength and decreased ductility, toughness and intergranular corrosion resistance.