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TÜV AUSTRIA Group's cathodic corrosion protection expertise
Our TÜV AUSTRIA Group corrosion experts at TPA KKS GmbH and METALogic look forward to receiving your inquiry.
Corrosion caused by potential differences between metallic materials and their environments
Corrosion is always due to potential differences between a metallic material (e.g. a pipeline) and its environment. It is an electrochemical process in which material is removed from the metal surface. Passive protective measures, such as sheathing or coatings, do not offer sufficient protection in practice, since even the smallest damage or scratches in the sheathing can cause severe corrosion damage. Comprehensive protection is therefore only offered by a combination of passive and active protective measures, such as cathodic corrosion protection.
The corrosion process can be actively influenced by applying an electrical voltage between metal and ground. The cathodic corrosion protection causes a potential reduction and thus reduces the corrosion erosion rate to a technically negligible value (approx. 0.01 mm per year).
Cathodic corrosion protection systems
There are basically two options available for the implementation of active corrosion protection or cathodic corrosion protection: Cathodic protection with external current or with galvanic anodes.
TPA KKS - TÜV AUSTRIA Group subsidiary V&C offers both design variants, but prefers to work with cathodic protection for buried structures.
In cathodic protection with external current, the required protective current is generated by a rectifier and fed into the ground to the object to be protected via external current anodes. The main advantage of this method is that the output voltage can be adapted to the resistance conditions of the ground and the protection current requirement of the pipeline as required. Cathodic protection also enables automatic status detection of the objects to be protected, so that possible irregularities can be detected and corrected immediately.
The anodes required for the protective current feed can be installed either horizontally or vertically in the ground. Depending on the local installation conditions, mainly FeSi anodes are used individually or ready for installation as container anodes with backfill. The effectiveness of the cathodic protection is monitored by potential measurement via permanent reference electrodes at measuring points. The necessary cable connections of the pipeline, the rectifier and the continuous reference electrodes are also brought together at the measuring points.
For smaller protected objects where no economically justifiable grid connection for an external current protection system can be established and the ground resistance is below 100 or ideally 50 Ω, cathodic corrosion protection with galvanic anodes is used. In this case, the required protective current is exclusively due to the different potential of the base anode material compared to the object to be protected without an external power source.
Due to the comparatively higher voltage difference compared to anodes made of zinc and aluminium alloys, anodes made of special magnesium alloys are mainly used for the protection of buried pipelines. The required number and size of the anodes depends on the size of the object, the specific ground resistance of the environment and the planned duration of protection. In order to reduce the contact resistance of the anodes in the ground, V&C supplies them preassembled in bags with a special backfill. Galvanic anodes are usually used up after a maximum of 20 years and must be replaced.
Lab tests
- Exposure tests
- Customized test procedures
- Electrochemical impedance spectroscopy
- Simulation of environmental influences
- (Cyclic) salt spray tests
- Materials testing
- Error analysis
- Cyclic polarization tests
On-site services
- Corrosion analysis of sprinkler systems
- Corrosion and coating inspection of underground tanks
- Study of soil corrosion and cathodic protection
- Endoscopy
- Replica examination
- Corrosion and coating monitoring
- Integrity measurement by means of sound emission
Further services
- Corrosion engineering and consultancy
- Training & further education