Failure Analysis of Ball Valve Made of Stainless Steel in Ammonium Phosphate Solution

The macro appearance,morphology and metallographic structure of ball valve which was made of stainless steel and failed in ammonium phosphate solution,were observed by metallographic microscopy and scanning electron microscopy(SEM).Also,photoelectronic direct reading spectrometer,energy dispersive spectrometer(EDS),carbon and sulfur analyzer and NHO-analyzer were also used to analyze the chemical composition of the substance and particles deposited on sealing area.The failure of ball valve was caused by electrochemical corrosion and scaling resulted from interaction of inferior materials and environmental medium.The corrosion mechanisms of stainless steel in ammonium phosphate solution were addressed and countermeasures for solving the problem were proposed as well.