MITIGATING FLOW-ACCELERATED CORROSION IN COMBINED-CYCLE AND COGENERATION PLANTS - BEST AVAILABLE PRACTICE

摘要

Flow-accelerated corrosion (FAC) is regarded as an increasingly common and very insidious type of failure mechanism in Heat Recovery Steam Generators (HRSGs) of combined-cycle and cogeneration plants by industry surveys. It consistently ranks high with thermal fatigue and corrosion fatigue, all reportedly ahead of 4th-ranked under-deposit corrosion. The proper management of FAC is of paramount importance since fatal injuries to workers have occurred in several power plants, and hundreds of piping and equipment failures have led to production losses and rising maintenance costs. There are two types of FAC - single-phase and two-phase FAC, quite different in character and root cause. The troubleshooting of FAC can be complex, and distinguishing between the two types is essential to understanding the issues in contention and to the amelioration of the FAC problem. Many key variables play a role in FAC - mainly system hydrodynamics (system geometry, fluid velocity, steam quality, temperature), materials of construction as well as operating practices. Water or cycle chemistry, however, plays a relatively minor role. All of the above complexities have created confusion and conflicting opinions amongst independent power industry players worldwide. This paper presents several case studies together with Best Practice guidelines that are invaluable to owners and current operators of combined cycle/cogeneration plants as well as those involved in all design phases of such projects, through the potential incorporation of these best practices at the earliest possible stage.