Failure Assessment of Heat Exchanger Tubes Due to Grooving Corrosion

Failure assessment was carried out on admiralty brass tubes in a heat exchanger that failed after five years of service. The failed tubes had numerous circumferential grooves on the external surface due to ammonia corrosion. Inside the brass tubes, a thin layer of calcium carbonate and a minor dirt material was deposited. Under the carbonate deposits, shallow pitting corrosion was identified. Additionally, dezincification was also noticed on both external and internal tube surfaces. The failure assessment was carried out by metallographic examinations, X-ray diffraction phase analysis, scanning electron microscopy, and elemental analysis. The investigation revealed that steam passing over the tubes was contaminated with ammonia compounds, causing groove corrosion. It was also noted that cooling water running inside the tubes had improper quality, leading to deposit formation. The failure investigation suggested that the brass tubes suffered severe grooving corrosion, pitting, and dezincification. The co-occurrence of these corrosion mechanisms on both inside and outside the tube surfaces led to the tube material thinning, weakening, and failure.