Localized Corrosion Behavior of Welded Pipes for Fresh Water Systems in the Shipbuilding Industry

Pipelines employed in cold and hot potable water systems in shipbuilding industry might be subjected to uniform and localized corrosion due to contact with chlorinated water. Moreover, cleaning products might cause corrosion attack. Corrosion might be enhanced by relatively high service temperatures (50¢ª-70¢ªC).
AISI 316 stainless steel and Cupronichel 90/10 (UNI 6785) are employed for pipeline construction. Stainless steel pipelines are constructed with welded pipes. The coupling of stainless steel pipes is made either with butt welds or through direct fitting by means of a deformable joint with O-ring between pipes and components (pressfitting). Cupronichel pipes are seamless and joints between different components are made through pressfitting.
Stainless steel and Cupronichel pipes were initially characterized by means of optical microscopy and SEM-EDXS. Corrosion behaviour was investigated by means of potentiodynamic polarization in solution with 5 ppm and 50 ppm chloride content in order to simulate respectively standard working conditions and factory cleaning of the pipes. Corrosion measurements were carried out at room temperature and at 55¢ªC. Moreover, the effect of welds on corrosion behaviour of pipes was investigated by means of electrochemical micro-cell technique, which enables localized corrosion measurements on the weld and in the heat affected zone.