Flow accelerated corrosion (FAC) is a combined form of erosion, corrosion and Cavitation. This is prominent in steam condensate lines which results in fast reduction of thickness in piping, piping components and valves. It is estimated that this problem is faced by majority of plants. There has been an increased emphasis on correcting these problems due to fatal accidents that occurred in 1986, 1995, 1996 and 2004 at various locations around the world. [3] After commissioning of the plant, Steam condensate system erosion/corrosion problem started appearing within one year of operation. To ensure uninterrupted plant running on line sealing was done and monitoring was done by proper thickness checking. These on line sealing points were replaced during available opportunity. In some cases plant shutdown was taken to replace leaking piping components & these incidents resulted into revenue loss to company. Aggressive inspection programs were taken up for thickness measurement on condensate lines and as a proactive measure, elbows were encapsulated with higher size elbows, reducers by on line welding/furmaniting with special clamps. Similarly gate and globe valves in condensate service also started failing as a result of erosion of body seat rings. Globe valves installed on bypass lines of control valves were found passing. Once these valves were operated for maintenance of control valves they could not be closed. In some cases valve body developed leak due to high velocity erosion. Various studies conducted for replacing these components by higher schedule fittings & pipes but it did not improve the situation except for slight increase in life of these components. Velocities were calculated at various locations and higher velocity, condensate impingement/cavitation was found as root cause of problems. This problem was solved by various methods like using higher metallurgy P11, P22 material, line size increase with increase in control valve sizing, lay out changes etc. This helped in improving reliability of condensate system and reducing risk associated with failure of piping. This paper presents a variety of cases where single-phase and two-phase steam flows, caused erosion-corrosion damage mainly at turn points of elbows and valves. It was observed that the presence, even of a small amount of the vapor phase can significantly increase the velocity of the condensate. This paper describes the mechanism of failures by study of the failed components, operating conditions & piping lay out. In this study velocity of steam /condensate at reducing section was found to be very high. Other various contributing factors like control valve / piping sizing, metallurgical requirements, effectiveness of steam traps, flow velocity and valve design (globe & gate) were also studied. The main causes of the failures are discussed and recommendations are provided to rectify the root cause of the problems & avoid similar problems in the future.
