Acid cleaning of thermal desalination plant: do we need to use corrosion inhibitors?

One feature of the operation of thermal desalination plant is the necessity to undertake occasional acid cleaning of the brineside of heat-transfer tubes. It is standard practice to incorporate a corrosion inhibitor in the acid cleaning solution but the choice of inhibitor may be complicated by the multi-metal equipment through which the cleaning solution must flow. This paper presents the findings of a laboratory experimental investigation aimed generally at simulating the conditions during acid cleaning operations but involving the relatively severe hydrodynamic aspect associated with jet impingement of acid on a material. In the absence of an inhibitor, the corrosion behaviour, of a range of materials employed in thermal desalination plant, was studied, using electrochemical and weight-loss techniques. The test solutions comprised aerated acids of pH = 2 at 20-55°C. The findings from the study, together with other data in the literature, are used as a basis for a discussion of whether there is a need for the use of a corrosion inhibitor during acid cleaning-especially in view of the relative infrequency of such cleaning operations consequent upon the performance of modern scale-control chemicals.