## 1 Introduction
[PERSON] [19] reported the successful performance of an arc sprayed TSA coating in a saline-mud environment typical of the deep Gulf of Mexico. The report was based on 4 and 12-month exposure tests conducted in natural Gulf of Mexico seawater (15 \({}^{\circ}\)C) and mud (7.7 \({}^{\circ}\)C), and included TSA coating performance data in terms of its ability to provide adequate cathodic protection for various amounts of exposed steel. The author concluded the life expectancy of aluminium-silicone sealed TSA coatings of 0.01 inch (254 \(\upmu\)m) nominal thickness with up to 5% coating holiday area to be typically greater than 25 years in such saline and mud environments. [PERSON] [20] conducted a performance review on the application of a TSA coating (99.5% aluminium) on production risers in a subsea environment. The internal temperature of the riser was reported to be about 80-90 \({}^{\circ}\)C with a surrounding seawater temperature of about 4-10 \({}^{\circ}\)C. The author reported that a 200 \(\upmu\)m TSA coating sealed with aluminium-silicone is capable of providing corrosion protection in seawater in excess of 20 years. Although TSA has been used in the offshore sector for decades, it is not always evident how it performs over the long periods required today by the offshore wind sector, particularly in the presence of damage that might occur during installation or in service. Literature data suggest that the focus thus far has been on the performance evaluation of TSA coatings under seawater immersion service. However, published work on TSA with damage has been limited to exploring the effect of single, small-scale damage on the corrosion performance [21]. The damage has been restricted in these studies largely to ~5% of coating area. Damage in service is not limited to 5% and the nature of damage during transport, installation or service is not restricted to a single holiday. Detailed experimental study on the effect of multiple damage/holiday or large-scale damage, such as 18-20% exposed area, has not been carried out. Furthermore, the vast majority of published information on coatings with damage only refer to short-term tests [22]. Thus, long-term performance data on damaged TSA would benefit the offshore energy community. As previously mentioned, the limited studies with damage in TSA restricted the damage to 5%. In limited cases where a larger damage area was used [23], detailed systematic study was not carried out to fully explore the corrosion or protection mechanism. Detailed study on the corrosion mechanism of thermal spray coatings, including the use of organic sealants, have been reported [24]. Some work on the corrosion mechanism in the cathodic region of exposed steel provided useful information for situations with one 'damage' area of 5% [25]. The corrosion products on the TSA and the defect area vary and can provide valuable information on the corrosion mechanism [26]. Laboratory and field trials have provided useful information on the products of the corrosion process [27; 28; 29; 30; 31; 32]. However, as indicated earlier these reports only provide information on coatings that fully cover the steel, or in the case of intentional 'damage', only provide data with one single area of exposed steel. Even the modelling work on TSA with damage has focused on simple'single' damage area [33]. The lack of detailed work on the effect of damage was also highlighted in the review on TSA by [PERSON] et al. [4]. Thus, understanding the mechanisms that govern long-term performance of TSA, especially when damaged, is important. The corrosion mechanism leading to loss coating is a key aspect. However, deposits formed on exposed steel may also play a significant role and impact the corrosion rate. These deposits formed on the damage areas need to be evaluated in terms of phases, microstructure and pore architecture to appreciate their impact on the corrosion process. The work presented in this paper addresses some of the knowledge gaps presented above.