Lime scale/Corrosion in heating systems

In raw waters, which are not separately treated, the formation of calciferous deposits take place depending on the content of calcium salts (the degree of hardness) and the temperature.
 These calciferous deposits, also known as boiler scale, usually occur above temperatures of 70°C and are related to escaping carbon dioxide and consequently exceeding the solubility level of the lime solution. Calciferous deposits are generally undesirable and can have the following effects:

• form scales on the metal surface, that insulate and severely hinder the heat transfer
• depending on the lime covering, surfaces with varying temperatures develop, which can lead to sudden water evaporation on the overheated metal (boiler scale explosion).
• contamination of a system with loose lime flakes
• concentration of chlorides in the porous lime layer with the consequent danger of severe crevice corrosion in stainless steel materials.

Calcification can be efficiently removed with organic acids. However, when dealing with un-alloyed steels, it is necessary to prevent the steel from attack by using a suitable inhibitor. Once the lime scale is removed the function of the component or system is re-established. Applying a final conservation to such components creates a good basis for further operational efficiency.

Corrosion in heating systems:

Immediately after operation begins, a thin iron-rust/lime protective layer forms in the standard closed heating systems of unalloyed iron materials. This can constitute a lasting protective layer due to the lack of a fresh oxygen supply. After the initial corrosion due to oxygen, this is all used up and the reaction stops because no new oxygen is available. However, it is important, that the same water continues to circulate in the system and that no fresh water – bringing in fresh oxygen - is added. The pH value must remain in the neutral range. Due to not totally gas tight of  the former synthetic pipes used for under-floor heating, which were laid in or prior to 1982, the oxygen absorbed in to the water was  far too much. The result was severe corrosion problems, which in some cases caused hold-up circulation. Today the synthetic pipes used for under-floor heating are sufficiently oxygen-tight and so do not pose any danger.