Cathodic Protection of Tap Water Distribution Networks – Guldager System

Operation Principle

The Guldager system ensures the cathodic protection of boilers and water pipe networks with the application of the mixed active impressed current and the aluminum electrolytic dissolution cathodic protection method. The system is considered necessary in situations of corrosive water use in combination with other unfavorable factors, such as high temperatures developed in the boiler, which can generate highly corrosive conditions.

Furthermore, in multiple applications it is desirable to maintain the highest possible temperature in the boiler in order to maximize the thermal energy and also to ensure hygiene parameters and water disinfection (e.g. Legeonella issues). It is noted that a 10 degree Celsius increase in temperature doubles the rate of corrosion.

The main advantage of the system lies in its potential to protect already corroded networks and thus prevent / discontinue certain effects such as red colored water coming out of the tap, without deteriorating the potable quality of the water.

Technical Description

For the protection of the pipe network, the aluminum anodes are installed in one or more boilers and the corresponding control unit is modified accordingly, in order to provide each tank with the required cathodic protection and the simultaneous dissolution of the aluminum anodes, depending on the inlet water flow. The unit receives signals from a pulse flow meter installed on the cold water inlet and provides a constant aluminum concentration in the water at the range of 0.1 – 0.2ppm. This value allows the formation of a protective layer of aluminum along the length on the pipe network, which remains under the national safety level limits for potable water.

In parallel, oxygen is produced at the permanent anode, contributing to the formation of the protective layer and the preservation of water freshness.


The aluminum electrolytic dissolution method is scientifically established and has been successfully applied for decades. Essentially, it consists of the single reliable protection method against corrosion of extended networks with relatively small diameter pipes. Being scientifically proven that the remaining methods of protection against corrosion, such as magnesium anodes for example, may not be used for the protection of small pipe diameter extended networks, the Guldager system presents the following major advantages:

  • No deterioration of water quality. Water remains at potable levels after treatment, since the aluminum concentration does not overcome 0.2ppm, which corresponds to the allowable aluminum level according to the World Health Organization (WHO) and the Greek Regulations (FEK 53 1986).
  • The system can be applied to already corroded networks without the need for pre-treatment.
  • The system has minimum maintenance requirements and low cost of consumable materials.
  • The specially designed electronic control system allows the monitoring of the proper operation of the system and the application of corrective actions without the need for a technician visit.
  • The system is installed after a careful study of the particular network characteristics, water quality, and mechanical installations. The study is conducted by experienced and specialized ensuring the most reliable and economical solution.

Reliability – Warranty

The impressed current cathodic protection system has been applied for more than five decades on structures that are subject to severely corrosive environments (ships, platforms, pipes, cooling systems, boilers) and is the only active corrosion protection method available for metal structures.

Particularly with regards to the method of elelctrolytic dissolution of aluminum, it is noted that the first such system was initially installed in 1924 and is still in operation. Currently, more than 40.000 such applications are in operation world-wide. In Denmark, where the system was invented the planning authorities consider erroneous the omission of electrolytic aluminum dissolution corrosion protection on the hot water distribution pipe network in new buildings.

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