Corrosion monitoring. Methods of corrosion monitoring in water-carrying systems

A collation has been made of the methods available for corrosion monitoring in liquids. Examples of the types of installation where these methods can be used are: * cooling systems. * process water systems. * hot-water systems. In these systems it is often suitable to limit the corrosivity of the liquid by, for example, removal of oxygen, changing the pH value or using corrosion inhibitors and other additives. In such cases corrosion monitoring aims at the best possible treatment of the liquid with regard to its corrosivity. Measurement of weight-loss is the most direct way of measuring the development of corrosion. It does, however, have the disadvantages of providing more work when evaluating and is slower than other methods, i.e. it requires long exposure times in order to give reliable results. The resistance method implies that one measures the resistance of a thin wire or film of metal. If this wire or film corrodes its resistance increases because of the reduction in cross-sectional area. The polarization-resistance method is an electrochemical method which in its simplest form means that a test probe with two electrodes of the material under study is exposed to the corrosive medium. Corrosion potential measurements give a measurement of the prerequisites of corrosion. Redox-potential measurements are used primarily for corrosion monitoring in systems which contain stainless steel and other metals which can be rendered passive and where there is a risk of pitting. Chemical analysis of components in the liquid which are vital from the corrosion viewpoint can be made when the aim is corrosion monitoring