Petrochemical Plant Injury Law And Safety Assessment Techniques Pearlitic Heat Resistant Steel

Pearlite heat resistant steels used in the petrochemical industry devices generally work under the high-temperature pressure condition. Under the circumstances that temperature and pressure act on for a long time, a series of changes will take place to the microstructure of the material such as pearlite spherodization, alloying elements impoverishment and carbide growing. These microstructurai degradation behavior makes high-temperature performance of material drop, leads to the pipe bursting ahead of time, and influences the safe operation of the petrochemical industry devices. Therefore it is necessary to research the damage law and security access technology of the pearlite heat resistant steels.This paper studies three pearlite heat resistant steels 12Cr1MoV , 1Cr5Mo and 20 steel which are commonly used in petrochemical industry devices. Through high-temperature aging experiment of different temperature and different time , make the microstructure damage in various degree. Microstructure changes are researched by SEM, EPMA, OM and image analyzer. At the same time, the material which has typical microstructure degradation state carries on normal temperature, high temperature short-time mechanical property experiment and creep-rupture strength experiment in order to analyse the impact of microstructure degradation on material performance.Through above-mentioned experiment, the microstructure changes law of three kinds of steels has been summarized, and kinetics formula of carbide coarsening is obtained. Tensile fractography indicates that the fracture is all typical ductility fracture. The quantitative analysis of some alloying elements (Cr , Mo ) of 12CrlMoV aging for 900 hours indicates that the impoverishment of Cr is not remarkable, but the impoverishment of Mo is obvious. Because of the impoverishment of Mo, solid solution strengthening decreases, and this is one of the reasons why material performance reduces.This paper discusses the strategy to evaluating residual life of three kinds of pearlite heat resistant steels. It has been shown that the creep-rupture strength decreased with microstructurai degradation. The relationship based on Larson-Miller method can be expressed as :P =Z -Z1lgσ - Z2 σ or P=Z0 -Z -Z1lgσ - Z2σ , where Z is a parameter related to degradation of creep-rupture strength. The residual life reduces with microstructurai degradation, and the corresponding curve moves to the left which makes Z changed. The relationship between creep-rupture strength deterioration parameter Z and microstructurai degradation parameter E is founded. So the residual life can be predicted by analyzing the microstructurai degradation of the components.This project which is the horizontal subject cooperating with Dalian Petrochemical Industry Company has already passed the confirmation on 12/9/2003.