STUDY ON THE USE OF CHLORINATED RUBBER PAINT
FOR MACHINERY BILGES

1. Introduction:- Maintenance of machinery bilges has always been a challenge to the maintainer due to poor accessibility and unavoidable effects of running machinery such as spillage of cooling sea water, spillage of fuel, spillage of lub oil, high ambient temperature and drainage of hot water below feed quality (in case of steam driven machinery). Coal tar epoxy paint (CTE) has been in use in these bilges. However the expected life of CTE could not be achieved, in many cases, as stringent surface preparation standards (Grit blasting to Sa 2.5) specified for the paint system could not be achieved prior to application of CTE. Creating sufficient accessibility to undertake grit blasting in machinery bilges has also been found to be extremely demanding in terms of time and effort, even during an MR when the engine bearers are thoroughly surveyed. Hence it can be seen that the ideal paint scheme, for machinery bilges, would be one which can accept the standard of surface preparation achievable by means of manual methods, in poor accessibility conditions, typical of a machinery compartment, often with the vessel afloat. Paucity of time required for boxing up of refitted machinery, critical for undocking, often restricts the possibility of undertaking painting in machinery bilges during the docked time. Chlorinated rubber based paint applied by brush has been tried out as an alternative paint system. This paper is a report on a case study of the application of chlorinated rubber paint in the bilges of INS Fiction. 2. Paint Specifications: - The chlorinated rubber paint system consisting of Paint Priming Chlorinated Rubber (Pattern number: 8010-000460) and Paint Finishing Chlorinated Rubber (Pattern number: 8010-000431), Brushing type, as per specification DEF STAN 80-72/1 was used for trials. The system is reported to have good resistance to acid and alkali and good outdoor durability. The normal system consists of one coat of primer and one coat of finishing paint. Such a system applied to clean steel and exposed to outdoor weathering conditions in temperate climates is expected to have a life of at least 4 years. The system used onboard Fiction consisted of one coat of primer and two coats of finishing paint. The paint was procured as per the above specification after quality clearance from CQAE(NS), Mumbai.

3. Surface Preparation:- As cited earlier, the chlorinated rubber paint system was chosen for its adaptability to a surface preparation standard lower to that achieved by grit blasting to Sa 2.5. In the case of Fiction the surface preparation was undertaken while the ship was afloat. The existing CTE paint was removed by scraping using manual tools. The surface was thereafter cleaned of dust and dried. The achieved surface naturally did not merit classification under any standard. However all efforts were made to achieve bare metal surface.

4. Paint application:- One coat of primer was applied on the bare metal surface, so achieved. The primer was allowed to dry for 24 hours. Two coats of chlorinated rubber paint finishing, white, were applied on the primer coat, with an inter-coat interval of 24 hours. The painting was completed on 18 Aug 2000.

5. Observations: - The performance of the paint has been observed since Aug 2000. Following are the observations:-

(a) The paint has been adhering well and no case of loss of adhesion to the substrate has been noticed. (b) Resistance to sea water and oil spillage has been very good. Discoloration has been noticed in areas where the paint had been exposed to seawater spillage. However these have been touched up after thorough cleaning, no loss of adhesion has been noticed.

(c) The quick drying nature of the finishing of coat has been found to be a very attractive feature of the paint system. This has a lot of advantages in that maintenance work can be undertaken while at sea with minimum machinery down time.

(d) Change of bilge paint colour to white has also been a very welcome feature. As discoloration or rust stains are highly visible, maintainers are warned sufficiently early for over coating after surface cleaning.

(e) The paint system has been found to be easier to handle as compared to CTE.

(f) Certain photographs of the painted surface are placed at Appendix P for appreciation.

6. Conclusion: - The chlorinated rubber paint system has been observed to be performing well for the last eight months. Several other ships have also subsequently used the scheme in machinery bilges. The chlorinated rubber paint scheme appears to be suitable for machinery bilges considering the difficulties of surface preparation in the bilges and the ambient conditions.

7. Recommendations:- Following are the recommendations:-

(a) Prospective supplier of the paint be allowed to study the environment more closely and take up one sample bilge area in each class of ship for undertaking painting, observation of its performance and using the results for fine tuning the composition for enhanced performance.

(b) Specification of the paint be reviewed in-house to review qualification requirements for the specific end use of protection of the bilges for various classes of ships, based on different ambient conditions depending on the type of machinery installed.