Information on copper pipes:

COPPER PIPES IN HEATING SYSTEMS

Combining copper and steel in the heating network

Heating equipment is expected to provide several decades of service life. This is required particularly of piping and radiators because their replacement is fairly expensive and highly disruptive of normal living comfort. Designers and clients are therefore justified in demanding durability from raw materials. Although copper satisfies these requirements admirably, it is sometimes assumed - erroneously - that corrosion damage will occur in systems where copper is combined with steel or iron-containing components.

Free oxygen is required to support the corrosion reactions taking place in piping networks. By removing the oxygen dissolved in the water the cathode reaction is eliminated and the anode reaction that dissolves metals is halted. In properly constructed and utilised heating equipment there is no longer any dissolved oxygen in the water. The systems are built to remove oxygen from the heating water and prevent the penetration of fresh oxygen.

In connection with the equipment's first filling all oxygen is removed from the water either by using inhibitors or by consuming the oxygen naturally in rapidly occurring reactions.

Different heating systems

In closed heating systems with sufficiently large membrane expansion tanks, structural measures are enough to prevent corrosion from occurring. Care must however be taken to ensure that the system in its entirety is sealed and that it is not necessary to add circulation water in normal conditions.

In systems equipped with open expansion tanks the penetration of oxygen cannot be prevented with absolute certainty. In these kinds of networks concentrations of oxygen in the circulating water must also be monitored and if necessary inhibitors added.

In open systems where water is added regularly, the penetration of oxygen cannot be prevented by structural means. For that reason, chemicals such as sulphites or hydrazine hydrates are added to bind the oxygen into an inert compound.

The positive long-term practical experiences gained from many different types of buildings have clearly demonstrated that copper stands up well in heating equipment and poses no threat to the durability of other materials.

Experiences with domestic water systems.

Clear differences in local conditions are an obstacle to assessing the practical experiences gained with the use of domestic water in heating equipment. Besides copper, these experiences also apply to all other metals.

Based on theoretical speculation and the experiences gained with domestic water pipes, two claims are often made that would appear to question the wisdom of using copper in heating systems.

It is claimed that galvanic corrosion would occur at junctions between dissimilar metals. Galvanic corrosion is however electrochemical by nature; this kind of corrosion cell functions only if oxygen is available in the cathode surfaces' reactions. In deoxygenated heating water galvanic corrosion as well as other forms of electrochemical corrosion are impossible.

In the brass valves and fittings of heating devices manufactured with steel pipes, as well as radiators manufactured from steel, there have always been countless points of contact between different metals that have not caused any damage as long as the construction and utilisation of the equipment has complied with the appropriate instructions.

The second claim opposing the combination of steel parts and copper tubing in heating equipment is based on a matter that is valid in domestic water containing oxygen. There it is a question of copper dissolving into the water during the initial phase of the copper pipes' use. When domestic water contains oxygen, it is also important that water with copper concentrations is not led to galvanised or black steel pipes where copper precipitation in the water causes so-called microgalvanic corrosion. In domestic water systems copper pipes are always installed last in the water's flow direction, for example: galvanised steel pipe à copper tube .

In closed heating systems water with copper concentrations poses no risk of corrosion to other materials because all electrochemical reactions - as well as microgalvanic corrosion resulting from precipitating copper ions - are impossible owing to the water's lack of oxygen . The materials' installation sequence is also of no consequence, nor can it be, because the same water is constantly recirculated in the heating system.

Oxygen concentration of recirculating water in heating network

In the corrosion process metal reacts primarily with the surrounding oxygen. In oxygen-free environments (for example in heating water) corrosion cannot occur. For this reason it is possible to combine dissimilar metallic materials. In experiments performed with softened low-oxygen (approximately 0.030 g/m 3 ) heating water it was found that even the addition of large copper concentrations to the water has no effect on the steel parts' corrosive flow.