Assessment of Coating Performance for Underground Pipeline

• Main Author: Ibrahim, Azman
• Format: Final Year Project
• Language: English
• Published: Universiti Teknologi PETRONAS 2014
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://utpedia.utp.edu.my/14422/1/13706.Azman.Ibrahim%28Hardbound%20Dissertation%29.pdf; http://utpedia.utp.edu.my/14422/
• Institution: Universiti Teknologi Petronas

The integrity of underground pipeline relies on the performance of the coating system. In this paper, electrochemical impedance spectroscopy (EIS) was used to evaluate the protective ability of polyamine cured epoxy coating in term of dielectric performance in NS4 simulated soil solution. The objective of this project is to assess the performance of good coating and physically-damaged coating of polyamine cured epoxy by obtaining the dielectric properties in simulated soil solution by using EIS and to determine the effect of coating condition on corrosion rate. The polyamine cured epoxy coating was applied to the carbon steel using airless spray gun. The thickness of coating was set according to the manufacturer specification. For physically-damaged coating, intentional coating flaws were made by stripping the coating. The EIS measurements were conducted by using three-electrode electrochemical cell system; X65 carbon steel samples (WE), a reference electrode and a counter electrode. The cell was filled with simulated soil solution (NS4). The frequency of the EIS measurement was ranged from 0.01 Hz to 100 kHz with an applied AC perturbation of ±10 mV. Based on the Bode plots, the damage coating samples showed low values of impedance compared to good coating. The results show that the damaged coating has reducing the strength of bonding between the coating particles. In term of dielectric properties, it is proposed that a coating system with good performance against corrosion show high values of and and low values of and . Based on the results, the values of and of good coating is higher than physically-damaged coating while the values of and is lower than physically-damaged coating. After 24 hours of immersion, the corrosion rate obtained from the good coating sample is 0.10× mm/yr which is significantly lower than the corrosion rate of physically-damaged coating sample which is 0.06 mm/yr. The corrosion rate of good coating is considered negligible since the value of charge transfer resistance is very high. Based on the worst case laboratory testing, a good coating can provides acceptable corrosion protection for underground pipeline.