FAILURE ANALYSIS OF YELLOW PHOSPHORUS TANKS

During the pour of liquid phosphorus in a pouring hall,one of 37 similar low-carbon steel railroad freight tanks designed to transport a yellow phosphorus from a chemical-processing plant to user, that began leaking liguid phosphorus and caught fire.shortly afterwared, the tank on another car began leaking and a comprehensive failure analysis to ascertain the cause of the failure was conducted using chemical analysis, optical and SEM metallographic techniques.It was shown that the tank failed due to pitting and crevice corrosion,which occurred in areas where bare steel had been exposed from both break in the coating and mechanical scratches on the painted-steel.The presence of aggressive cover water containing phosphoric acid and having a pH of 1.61~1.83 was a factor accelerating attack. During long wet layup periods,the recommended practice is to fill the system with day nitrogen or with treated water to avoid corrosion.