PRESS RELEASE
November 20, 1995
Anodic protection
stifles liquor line corrosion

Equipment in the pulp industry, such as digesters, impregnation vessels, liquor clarifiers and storage tanks, is heavily exposed to corrosive chemicals and must, as a consequence, be appropriately protected.
An anodic protection system, developed by Finnish Savcor Consulting, has proved itself to be an efficient and beneficial method for liquor line corrosion prevention.

Digesters, impregnation vessels and storage tanks which handle caustic liquors, are traditionally made of carbon steel, which has proved itself to have reasonable resistance to corrosion in liquor. The resistance in alkaline environments derives from a protective, passive layer which develops on the surface of the metal.
However, the development of processes for improved productivity has changed process conditions and the chemical environment is today much more corrosive than it was ten years ago. This has been observed especially at mills with an extended cooking process. The natural oxide film is no longer resistant to corrosive attack from the chemical compounds in, for example, a pulp digester. Erosion or stress corrosion breaks the surface layer and can lead to deep cracks in the digester shell.
In anodic protection, the natural passivation reaction of carbon steel is accelerated by an electrical current supplied by rectifiers and cathodes. Anodic current creates and maintains a stable oxide film on carbon steel and makes it corrosion resistant, even in the harshest environments, and dangerous cracks by corrosion fatigue can be avoided.
Anodic protection efficiently prevents general corrosion, which is a severe problem for many digesters. An example: a digester was corroding at a rate of 3.5 mm per annum. Recent observations show that the thinning of the digester shell has stopped after the installation and start-up of a Savcor anodic protection system.
The system can be applied to existing equipment to lengthen the expected life time and to reduce maintenance costs. Anodic protection also offers possibilities to reduce investment costs of new equipment, since lower grade materials can be used for construction.
A typical Savcor protection system for a digester comprises cathodes attached to the digester shell, reference electrodes for measuring corrosion conditions, and a rectifier unit for the supply of protection current. Accurate current feed is controlled by a data processor with system software responding to changes in the digesting process. Real-time system data is displayed on a monitor. The whole system can also be connected to a Savcor remote control centre over normal modem lines. The system can also be connected to the mill DCS to provide valuable information on corrosion conditions and the process. Remote control allows for supervision of the corrosion inhibiting system thus ensuring a higher degree of serviceability.
The main advantages of an anodic protection system are extended lifetime for process equipment. In addition, the system results in increased productivity when shut-downs caused by corrosion failures can be avoided.
Savcor Consulting, with headquarters in Finland and subsidiaries or representatives in all major world markets, has been solving industrial corrosion problems since 1981. The company has successfully protected more than 40 kraft digesters and impregnators world-wide.

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Captions:

(1) Digesters, impregnation vessels and storage tanks in the pulp and paper industry can be efficiently protected against corrosion with an anodic system. The main advantages are extended lifetime for process equipment and the avoidance of unexpected shutdowns.

(2) A complete Savcor anodic protection system for a pulp digester comprises units from cathodes to remote control devices.
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For further information, please contact:

Savcor Consulting Oy
Mr. Jukka Rautiainen
Insinöörikatu 8
FIN-50100 MIKKELI, Finland
Tel. +358 55 760 400
Fax +358 55 760 4211