Abstract: The corrosion is resulting in serious economic loss and casully, the online corrosion monitoring, a new technology continuous ly measuring the speed of corrosion and the parameters related to the speed without impacting the normal operation of the system, is developped quickly. In demestic petrochmical enterprises, research and application of the technology become an important issue. Authors of the paper research the structure characteristic and pattern of two types of online corrosion monitoring systems, introducce three typical reliability models of system, i,e., reliability model of series system, reliability model of parallel system and reliability model of mixed structural system, and the last one is selected to analyze two types of online corrosion monitoring. On the basis of it, the reliabiltiy model of online corrosion monitoring system is established, the model can be used both to forcast the reliability of the standing up system monitoring facilities, andevaluate the reliability of online monitoring system in operation. At last, a case is presented to calculate the reliability, total rate of failure and average working time of some on0line corrosion monitoring systems.

Key words: corrosion, on line monitoring, structure, reliability, model