Increasing Corrosion Resistance of Pressure Vessels at the Hydrostatic Pressure Testing by Using Inhibitors

Studies of the corrosion initiation at the pressure hydraulic test of pressure vessels during their filling, maintaining and draining are presented. It has been established that the most suitable method involves the use of corrosion inhibitors, which directly decrease the corrosion rate even in small or very small quantities. It was studied the influence of some corrosion inhibitors at different concentrations on some steel materials commonly used at pressure vessels manufacturing. The study involved the inhibitors testing both in laboratory and in factory conditions. Testing in laboratory conditions involved the analysis of the following inhibitors: urea, thiourea, triethanolamine, FINEAMIN 88 and FINEAMIN 06. The results were compared with those of the Adirol inhibitor, the currently used inhibitor. It was investigated the corrosion of the following stainless steels and unalloyed steels: A 240 grade 304, A 240 grade 316, A 516 grade 70, A 516 grade 60, P260-GH, P265, P275, P295-GH, P295, and P355. By recording the potentiodynamic polarization curves, the corrosion parameters (corrosion potential, corrosion current density, polarization resistance, corrosion rate, charge transfer coefficients for anodic and cathodic processes, inhibitors acting coefficients, and inhibition efficiencies) have been evaluated. The following corrosion inhibitor solutions were selected for testing under the factory specific conditions: Instal Protect SP at concentrations of 5%, 7.5% and 10%, ELG INCOR SP at 10% concentration, FINEAMIN 06 at 10/00 concentration and a mixture of 40mL FINEAMIN 06 + 40 mL FINEAMIN 88 SCAV25 in 40 L water. The analysed steels were A 106 grade B and A 283 grade C. Tests in laboratory conditions revealed a different behaviour of the inhibitors, depending on the analysed concentration and steel grade. The inhibitors proven as appropriate following the tests in the factory conditions were ELG INCOR SP used in industrial water (tap water), whereas the mixture of FINEAMIN 06 + FINEAMIN 88 SCAV25 had efficiency only in demineralised water.