SAVCOR ANODIC PROTECTION

Savcor Anodic Protection (AP), is effective in very high or very low pH environments like in pulp digesters and impregnation vessels.

In an anodic protection 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 digester cracking by stress corrosion is also avoided.

When installed in old equipment, Savcor Anodic Protection System 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.

Typical targets for Anodic Protection :

Pulp digesters
Impregnation vessels
Liquor storage tanks and clarifiers
Sulphuric and phosphoric acid tanks
Sulphuric acid heath exchangers

Anodic Protection of Pulp Digesters and Impregnation Vessels

The Savcor Anodic Protection System consists of:

Cathodes 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

The first Anodic Protection System for a Pulp Digester was installed by Savcor in early 80´s. Savcor got an opportunity to test its new electrochemical technology in a digester that had already developed severe stress corrosion cracking and was threatened by closure. The AP worked amazingly well and digester´s life time was extended by tens of years.

Since then Savcor has protected pulp digesters and impregnation vessels all around the world.

SAVCOR AP REFERENCES

Digester stress corrosion cracking can be prevented

Digester stress corrosion cracking SCC can be prevented by anodic corrosion protection

Cracking of digester and impregnation vessel is a serious problem which can lead to catastrophic failures. With huge pressure vessels full of hot liquor, structural integrity should be a main priority. Anodic protection can prevent the initiation of new stress corrosion cracks and even stop development of existing cracking if the crack depth is moderate.

The first step is to find out if process conditions promote stress corrosion cracking (SCC) and if yes, can the process be modified so that the risk is mitigated. Savcor Digester Corrosion Monitoring system together with a comprehensive electrochemical study done in-situ will reveal the safe running modes and alerts when entering the danger zone. This is where our 40 years of experience of digester corrosion prevention really helps!

The Savcor actions against cracking of digester:

Installation of corrosion monitoring system and conducting an electrochemical survey where SCC risk potentials are mapped.
Reference electrodes supply on-line electrochemical potential data, detecting process conditions which can lead to stress corrosion cracking.
If SCC risk conditions can not be avoided, the corrosion monitoring system can be expanded to full Anodic Protection system, by adding current feeding electrodes and rectifiers with accurate control system
Rectifiers supply anodic protection current, passivating the vessel wall and preventing onset of stress corrosion cracking

SULPHURIC ACID TANKS

In sulphuric acid Anodic Protection passivates the steel by forming a protective ferrous sulfate layer on the metal surface.

Benefits of Anodic Protection in sulphuric acid tanks are lower maintenance costs due to mitigated corrosion, lower investment costs when choosing mild steel instead of stainless tank and minimizing ferrous contaminants in high purity acids.

Typically sulphuric acid storage tank AP operates best in ambient temperatures, 85 to 98% acid concentrations. Phosphoric acid tanks can also be protected.