Model of influencing factors for hydrogen damages of boiler evaporator tubes

Abstract

Hydrogen-induced fractures of metallic components of thermal fossil fuel power plants (TPP) presents very serious exploitation problem and often exert considerable influence on the loss of power plant availability. Hydrogen damage is one of the most disturbing of boiler tube failure mechanism, and from the international experience, remains as one of the leading causes of frequent outages of boiler tubing system. To clarify root causes and complexity of problems associated with hydrogen damages, it is necessary to apply a multidisciplinary approach which comprises research in the field of material quality, boiler design, operation and maintenance. The work reported here is based on the theory and, particularly, on the experimental tests performed on boiler evaporator tube samples, taken from a domestic 210 MW power plant, that had experienced hydrogen damages during service. Possible mechanisms for metal - hydrogen interaction are considered from materials point of view, fluid hydrodynamics in evaporator tubes and the complexity of structural - exploitation plant characteristics. The aim of this paper is to contribute to the analysis of hydrogen damaging in boiler evaporator tubes and to propose failure mechanism model based on "micro-departure from nucleate boiling" (micro-DNB) of working fluid. In addition, this paper elucidates some definitions of major root cause influences by proposing model for systematization of influencing and corresponding operating factors responsible for hydrogen damages of boiler evaporator tubes.