Abstract
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.
Highlights
Pressure vessels are usually installed in chemical and petrochemical industries
- Adirol has an inhibition efficiency over 90% at 10% concentration, except for A240-304, A240316 and P295 steels where its behaviour seems to be a corrosion process accelerator;
- FINEAMIN 06 and 88 have inhibition efficiency over 90% for all the concentrations, except for P295 where the efficiency is lower, whereas for some concentrations its behaviour is of a corrosion process accelerator
Summary
Pressure vessels are usually installed in chemical and petrochemical industries They can be column type equipment where substance transfer processes occur (absorption, desorption, chemisorption, rectification, extraction, adsorption), tanks for chemical products storage, heat exchangers containing cooling or heating fluids, and steam condensers. They are pressure vessels that act as buffer vessels (expansion vessels) for alternative compressors, both for aspiration and discharge. Depending on the compression steps, the pressure of the gases circulated in these pressure vessels increases even up to 300bar.These vessels are exposed to different environments and operating conditions by their scope, manufacturing process, tests they are subjected to, or storage conditions until their delivery. Corrosion represents a significant factor of the equipment durability and safety
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