Thermally Sprayed Aluminum Coatings for the Protection of Subsea Risers and Pipelines Carrying Hot Fluids

Nataly Ce,Shiladitya Paul

doi:10.3390/coatings6040058

Nataly Ce, Shiladitya Paul

Open Access

https://doi.org/10.3390/coatings6040058

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Abstract

This paper reports the effect of boiling synthetic seawater on the performance of damaged Thermally Sprayed Aluminum (TSA) on carbon steel. Small defects (4% of the sample’s geometric surface area) were drilled, exposing the steel, and the performance of the coating was analyzed for corrosion potential for different exposure times (2 h, 335 h, and 5000 h). The samples were monitored using linear polarization resistance (LPR) in order to obtain their corrosion rate. Scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were used for post-test characterization. The results showed that a protective layer of Mg(OH)2 formed in the damaged area, which protected the underlying steel. Additionally, no coating detachment from the steel near the defect region was observed. The corrosion rate was found to be 0.010–0.015 mm/year after 5000 h in boiling synthetic seawater.

Highlights

Coatings are applied on subsea pipelines to protect carbon steel from seawater corrosion, either by acting as a barrier or by providing sacrificial protection
Sprayed Aluminum (TSA) coatings are widely used in offshore industry as a long-term corrosion control method, suitable for structures subjected to temperatures exceeding 120 ◦ C where a minimum of 200 μm thickness is recommended [2,3,4]
Literature mentions that inadequate sealing and inappropriate Thermally Sprayed Aluminum (TSA) thickness can result in blisters and failure of the coating under certain circumstances [3,6]

Summary

Introduction

Coatings are applied on subsea pipelines to protect carbon steel from seawater corrosion, either by acting as a barrier or by providing sacrificial protection. Coatings for offshore applications must have specific characteristics, such as good adhesion to the steel, resistance to UV degradation, and thermal stability (amongst others), so that they can guarantee corrosion protection in the marine environment [1,2]. Sprayed Aluminum (TSA) coatings are widely used in offshore industry as a long-term corrosion control method (as sacrificial coatings), suitable for structures subjected to temperatures exceeding 120 ◦ C where a minimum of 200 μm thickness is recommended [2,3,4]. Sealer is often recommended for TSA to fill surface-connected porosities resulting from the spraying process and prevent the penetration of corrosive substance within the coating. Literature mentions that inadequate sealing and inappropriate TSA thickness can result in blisters and failure of the coating under certain circumstances [3,6]

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