ABSTRACT

Corrosion protection by a commercial phenolic epoxy coating for carbon steel panels was examined after exposure to a thermal cycling regimen of 22 °C and 120 °C for 40 d. The panels, along with freshly coated samples, were tested and immersed in solutions with 3.5 and 5 wt.% NaCl at 80 °C for 60 d. Some of the samples were also exposed to water condensation. Coating behaviour was investigated by visual observation (degree of blistering and evaluation of degradation) of coating, and electrochemical impedance spectroscopy (EIS). The EIS results, and the degree of blistering and delamination around the scribed regions of the panels suggested that 3.5 wt.% NaCl caused greater degradation than did 5 wt.% NaCl. Thermal exposure improved corrosion protection as evidenced by the higher impedance (>0.1 GΩ cm2) of the specimens, the absence of blisters on the panel surfaces and the reduced delamination around the scribe areas of the thermal cycling panels compared with the freshly coated samples. The results showed that the organic coating exposed to heat exhibited an improved resistance against severe marine conditions.

INTRODUCTION

Organic coating is the most widely used method of corrosion protection1,2. its corrosion protective abilities depend on physical, chemical and mechanical properties including adhesion to a substrate and essential barrier properties against corrosive species, such as water and oxygen 3,4. The durability of corrosion protection coatings is evaluated based on their effectiveness in providing long-term protection to metallic substrates when these materials are exposed to aggressive corrosion environments.

Coated carbon steel is widely used in marine environments. The main salt in seawater is NaCl, thus, 3.5 and 5.0% NaCl solution prepared from deionised water is often used to simulate the effect of salinity in marine environment. Salinity, moisture, and temperature generate internal stress in the coating, which is transferred to the coating/ substrate interface. This accelerates degradation in the coating which is observed by loss of adhesion or delamination of the coating. The reliability of a coating thus depends directly on saltwater corrosion protection.

Keywords:
corrosion management, h2s management, geologist, united states government, oilfield chemistry, australia government, geology, flowline corrosion, production chemistry, materials and corrosion
Subjects:
Production Chemistry, Metallurgy and Biology, Pipelines, Flowlines and Risers, Materials and corrosion, Well Integrity, Subsurface corrosion (tubing, casing, completion equipment, conductor), Corrosion inhibition and management (including H2S and CO2)
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