Corrosion inhibition of OFHC copper by prefilming with organic compounds

Abstract

As part of research on corrosion phenomena in the oxygenfree high conductivity (OFHC) copper pipes of the stator cooling circuit of a power plant turboalternator and the possibility of using copper inhibitors, some prefilming systems have been investigated, taking the common treatments with benzotriazole as a starting basis. The stability of the inhibiting layer, obtained in aqueous solutions of the inhibitors (pure compounds or their mixtures) at 40 and 80°C for 14 h, was evaluated by determining the polarisation resistance (Rp) of the prefilmed copper specimens during subsequent 6 h exposure tests in 0·1M NaClO₄ solutions, deaerated by nitrogen or saturated with oxygen and carbon dioxide. The following pure inhibitors were investigated: 1,2,3-benzotriazole (BTA); 5-hexyl-1,2,3-benzotriazole (C6BTA); trans-cinnamaldehyde (TCA); and their mixtures (in various concentration ratios): BTA+ TCA and BTA+MBT (2 mercaptobenzothiazole). Prefilming treatments showing the highest inhibitor efficiency were tested in aerated deionised water at 40°C for 30 days. The best results were obtained by prefilming the specimens at 80°C using 0·001M C₆BTA. The very good protective properties of this organic compound were confirmed in flowing conditions in tests of 30 days duration in recirculating pure water containing 500 ppb (parts per billion) of oxygen. A careful discussion of the properties of the copper inhibitor interactions on the basis of Rp data and some surface analysis data is also reported.