Water Droplet Impingement Erosion

Erosion. The abrasive is likely to be gas borne (as in catalytic cracking units), liquid borne (as in abrasive slurries), or gravity pulled (as in catalyst transfer lines). Because of the association of velocity and kinetic energy, the severity of erosion may increase as some power (usually up to the 3d) of the velocity. The angle of impingement also influences severity. At supersonic speeds, even water droplets can be seriously erosive. There is some evidence that the response of resisting metals is influenced by whether they are ductile or brittle. Probably most abrasion involved with hydrocarbon processing is of the erosive type. 

The metal loss and resulting split were caused by erosion from impingement of high-velocity steam in which droplets of water were entrained. The conical pinnacles in the affected region are typical of deterioration by this mechanism. 

Several environmental modifications can be implemented to minimize the risk of erosion corrosion. Abrasive particles in fluids can be removed by filtration or settling, and water traps can be used in steam and compressed air systems to decrease the risk of impingement by droplets. Deaeration and corrosion inhibitors are additional measures that can be taken. Cathodic protection and the application of protective coatings may also reduce the rate of attack. 

---