Exceptional performance from Jotun 'Tankguard Special'

Citation

(1999), "Exceptional performance from Jotun 'Tankguard Special'", Anti-Corrosion Methods and Materials, Vol. 46 No. 4. https://doi.org/10.1108/acmm.1999.12846daf.003

Exceptional performance from Jotun 'Tankguard Special'

Exceptional performance from Jotun "Tankguard Special"

Keywords: Joton, Marine corrosion, Coatings, Steel

Following its introduction two years ago, Jotun Paints' "Tankguard Special" phenolicepoxy coating system was used to refurbish the cargo tanks of the 18,700dwt Portuguese tanker Galp Leixêes. Apparently recent inspection of the tanks revealed no detachment or blistering of the coating, and only insignificant patches of corrosion.

When, in 1996, the Galp Leixêes drydocked for repair to her cargo tanks, a considerable amount of steelwork needed to be replaced, and the total area cleaned and coated, including both new and remaining old surfaces, was 5,500m2.

The vessel's tanks were surveyed by Jotun and, in accordance with the company's own "Tankcoating Code of Practice for Newbuildings and Ships in Service", the required high standards for the refurbishment were established with the owner and the yard.

The "Tankguard Special" coating system was recommended and comprises three coats, namely, "Tankguard Special Primer" (light red), Tankguard Special Mid-Coat (yellow), and "Tankguard Special Topcoat" (grey). For the Galp Leixêes each coat was applied to give a dry-film thickness of 100 microns, with a stripe coat before each full coat on difficult areas.

According to Jotun in addition to an excellent resistance to chemicals and solvents, including petroleum spirit with up to 20 percent methanol, the "Tankguard Special" system offers very good resistance to water, making it ideal for use in tanks containing "grey" water. In addition, the topcoat has a glossy finish and, hence, is easy to clean.

It is reported that at the recent inspection, the cargo tanks of the Galp Leixêes were found to be in excellent condition with no detachment or blistering of the coatings; the gloss finish of "Tankguard Special Topcoat" was found to be virtually "as new" .

The tanks were said to be generally clean with cargo residues detected only on some longitudinals and on the tank bottoms. We are informed that corrosion had occurred on only 0.2-0.3 percent of the tank-tops, and this was partly due to destaging damage which had not been correctly recoated afterwards. There were also minor spots of corrosion in difficult-access areas, and on steps and hand rails, with some staining on flanges.

Following the inspection and assessment, the rust spots on the tank tops were repaired, with a procedure involving degreasing, vacuum blasting to Sa 2ø standard, washing and touching-up with the three "Tankguard Special" coatings.

In order to obtain the best possible protection, the coating of tanks in a product carrier must be carefully pre-planned and conscientiously carried out, with the work being carefully monitored at all stages. There are many traps for the unwary.

Old steelwork, for example, will often be badly pitted and contaminated with salt. In such a condition, it is imperative that the surfaces are adequately cleaned before new coatings are applied.

Applying a coating over a salt film is a frequent cause of blistering. Although for a ballast tank coating, for example, a salt level of 50 mg/m2 is normally acceptable, the much lower level of approximately 10mg/m2 is essential to ensure the expected results from a product carrier cargo tank coating.

It is not always realised that salt contamination is seldom removed by blastcleaning alone, and that high-pressure water washing is needed before the final blastcleaning to Sa 2ø standard. In some cases, even this procedure will need to be repeated before the steelwork is fit to be coated.

In applying the coating, the manufacturer's recommendations should be strictly adhered to. For example, a stripe coat should be applied, by brush, to all edges, sharp corners, welding seams and other " difficult" areas prior to every full coat.

"Tankcoating Code of Practice for Newbuildings and Ships in Service", and a "Chemical Resistance" list for "Tankguard Special" are available, to potential users, from Jotun group offices worldwide.

Details from Jotun-Henry Clark Ltd. Tel: +44 (0) 171 481 2741; Fax: +44 (0) 171-265 1836; E-mail: linda.diamond@jotun.co.uk