Fault root cause tracing method of large-scale complicated equipment based on fault graph

Abstract

There are many types of large-scale complicated equipments in process industry. Accidents caused by faults of these equipments always lead to serious consequences. Fault diagnosis and root cause tracing based on FMEA and FTA are main ways to prevent abnormal events occurring on these equipments. Different from small equipment, large-scale complicated equipment always has numerous components and complex internal structure. FMEA has weak ability to represent the complex relation between faults of different component. Also, FTA modeling is time intensive and unreliable when equipment structure becomes complicated. According to these problems, this paper proposed a fault root cause tracing method of large-scale complicated equipment based on fault graph (FG). FG is a special kind of fault-oriented directed graph expanded from fault tree, which takes advantage of graph rather than tree to describe complex relation between fault modes of components, and add logic “AND” and “OR” connectives. FG is a useful tool to model the complex structure and fault affecting relation between components of large-scale complicated equipment in process industry, and can be used to trace fault root causes effectively in system failure of equipment. In this method, FMEA is used firstly to extract fault modes and fault affecting relation between components of equipment. The fault modes and their affecting relation are stored in polychromatic matrix. Then the polychromatic matrix of fault modes and their affecting relation is converted into FG automatically by algorithm with several rules. The FG can represent complex fault affecting relation between components of the equipment conveniently. The reachability from the failure nodes of FG is then calculated to obtain those possible fault transfer reachable components. The fault transfer pathways from root causes to failure component is searched based on graph-theoretic methods. An example of FG modeling and fault analysis of turbine which has complex internal structure and is widely used in process industry is introduced. The example proved that the proposed method is effective for fault root cause tracing of large-scale complicated equipment.