Life evaluation of organic coatings on hydraulic metal structures

Abstract

This paper presents the effects of tensile stress and corrosion environment on the protective performance of organic coatings on hydraulic metal structures. Accelerated ageing tests are performed on the organic coatings for 3600 h in UV-condensation test chambers and under immersion conditions. Gloss loss, color difference, thickness, rust area and adhesion of organic coatings are investigated. Acceleration coefficient between the accelerated ageing tests and the natural ageing environment are discussed based on the corrosion degree comparison method. The results show that corrosion degree of the coatings increases with the prolonging of the test time. Coatings are corroded more seriously in salt water than that in fresh water. Tensile stress accelerates the corrosion process of the organic coatings, and the corrosion degree of the organic coatings increases with the increase of stress levels. The corrosion process of the organic coatings could be divided into two stages: first stage is the time from the beginning to the appearance of rust; second stage is the time from the appearance of rust to the 5% of rust area rate. The gloss loss rate is chosen to evaluate the corrosion behavior of the coatings in the early stage, while the rust area rate is chosen to evaluate the corrosion behavior of the coatings in the middle and later stage. A life evaluation model of the organic coatings on hydraulic metal structures is established based on the acceleration coefficient. The influences of corrosion environment and tensile stress on the coating life are considered via the gloss retention coefficient and the corrosion inhibition coefficient in the model.