Assessment of zinc oxide-polyurethane internal coating for protection of ASTM A106 steel in seawater piping

• J.V. Jubilate¹, A. Pradityana¹, A. Safa’at¹, D.M. Kusnadi¹, F. Khosfirah², W.B. Wan Nik³, M. Ridha bin Muhamad⁴, M. Faizul bin Mohd Sobri⁴, N.Liana binti Sukiman⁴ and G. Yingxin⁴

¹ Dept. of Mechanical Industrial Engineering, Vocational Faculty, Institut Teknologi Sepuluh Nopember Surabaya, 60111, East Java, Indonesia
² Dept. of Mechanical Engineering, Faculty of Industrial Technology and System Engineering, Institut Teknologi Sepuluh Nopember Surabaya, 60111, East Java, Indonesia
³ Faculty of Ocean Engineering Technology and Informatics, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia
⁴ Dept. of Mechanical Engineering, Faculty of Engineering, Universiti Malaya, Kuala Lumpur, 50603 Malaysia

Abstract: This study evaluates the effectiveness of zinc oxide–polyurethane internal coatings on ASTM A106 carbon steel pipes exposed to a 3.5% NaCl solution. The testing was carried out using immersion testing, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and pull-off adhesion testing to assess corrosion resistance, corrosion rate, and coating adhesion strength. Corrosion rate results obtained from PDP testing were compared with those from immersion testing, indicating that short-term electrochemical testing does not fully reflect the long-term degradation effects observed in immersion tests. Coated specimens generally exhibited lower corrosion rates, with optimal performance achieved at specific zinc oxide concentrations. However, Specimen E (92.5% polyurethane – 7.5% zinc oxide) showed macrocracking after prolonged exposure, indicating that excessive zinc oxide content may lead to coating failure and exposure of the metal surface to corrosion. Pull-off adhesion testing and SEM analysis revealed that the addition of zinc oxide improved the mechanical strength of the coating, as demonstrated by Specimen C (97.5% polyurethane – 2.5% zinc oxide), which exhibited the highest tensile strength. In contrast, agglomeration due to high zinc oxide content in Specimens D (95% polyurethane – 5% zinc oxide) and E resulted in decreased adhesion strength and reduced corrosion protection. The uncoated specimen (Specimen A) exhibited a corrosion rate of 0.17139 mm/year, while Specimen D achieved a rate of 0.03352 mm/year, corresponding to the highest inhibition efficiency of 99.98% based on PDP results. These findings underscore the importance of optimizing zinc oxide concentration to achieve a balance between corrosion resistance, mechanical integrity, and coating durability in marine environments.

Keywords: pipe corrosion, coating, zinc oxide, polyurethane

Int. J. Corros. Scale Inhib., 2025, 14, no. 4, 2000-2016
doi: 10.17675/2305-6894-2025-14-4-15

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