In Anodic Protection (AP), the metal surface is polarized with rectifiers feeding direct current through cathodes. Anodic current forms a strong passive oxide film on carbon steel and makes it corrosion resistant, even in the harshest environments. Erosion corrosion or pitting corrosion cannot cause failures on surfaces with anodic protection. Dangerous cracks by stress corrosion are also avoided. When installed in old equipment, anodic protection prevents corrosion already in action.
The key for protection control is measuring the electrochemical potential of the protected structure. The required protection current is adjusted based on the potential values measured. In an Anodic Protection, the target potential is more positive than the natural potential.
Cathodes/anodes immersed in the process electrolyte
• reference electrodes which measure the potential level
• rectifiers for supply of protection current
• control unit with data processor for accurate current feed
• system software with correct responses to changes in the process
• monitor showing the real-time system data
• internet communication to Savcor Remote Control Center
Metsä Fibre, Kaskinen new mill had cracks in their impregnation vessel caused by stress corrosion. There was a threat of immediate close-down based on the pressure vessel code in 1983. In this desperate situation Savcor got a chance to test its new product, Anodic Protection, for the pulp digesting process. The AP-System stopped corrosion and the protected vessel remained operative for 25 years, until the mill was closed.
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