An Approach to Determine the Initiation of Carburization in a 304H Stainless Steel Piping under Petrochemical Environment

摘要

Carburization is a common degradation mechanism in carbonaceous gas streams at elevatedtemperatures in petrochemical industries. The crossover piping system between the convection sectionand radiant section of ethane cracking furnaces is fabricated from 304H stainless steel (SS), and isnormally protected by a chromium oxide layer. Carburization (and potentially metal dusting) forms oncedegradation of the oxide layer occurs during the ethane cracking/decoking process.A thorough metallurgical analysis demonstrated that some components of the crossover piping systemin one of our plants suffered from carburization and metal dusting. This paper describes a methodologydeveloped to determine the initiation point of carburization based on metallurgical analysis andtheoretical modeling. The predicted initiation point of carburization, using this approach, was correlatedwith a major process parameter change in the plant operation, which greatly reduced the protection ofthe aged 304H SS from carburization and metal dusting.Fick’s Second Law of Diffusion was applied to describe carbon diffusion kinetics into the bulk pipe steel,the heat-affected zone (HAZ) and the weld. It has been established through metallurgical analysis thatdepth of carburization of this particular pipe section followed a power-law relationship with carburizationtimes (in the unit of years). These relationships can be used to ascertain the initiation point ofcarburization for the HAZ and the bulk steel, thus providing important information for life assessment ofthis crossover piping system.