Design for coatings in ships ballast tanks R. Kattan and D Brodderick, Safinah Ltd, UK SUMMARY In July 2007, IMO adopted amendments to SOLAS by resolution MSC216(82) which put into force the Performance Standard for Protective Coatings for dedicated seawater ballast tanks in all types of ships and double-side skin spaces of bulk carriers, (PSPC). Compliance with the PSPC is also required by the IACS Common Structural Rules for Bulk Carriers and for Oil Tankers, which were adopted in December 2006. This paper considers the importance of ship structural design in the through life performance of coatings in ballast tanks. 1. INTRODUCTION Vessel losses have always been a source of concern to the marine industry. [1]. As a consequence the International Maritime Organisation (IMO) adopted a series of measures to improve bulk carrier safety [2]. One of the key causes of these structural failures has been established as corrosion and in particular corrosion in ballast tanks [3]. The industry first responded by introducing enhanced survey programmes and the effort to improve the corrosion protection of vessels has ultimately culminated in the adoption of the Performance Standard for Protective Coatings. 2. PSPC The IMO Maritime Safety Committee (MSC) identified that coating performance was of global concern for the safety and integrity of ships. Following a long period of technical discussion, the IMO Performance Standard for Protective Coatings (PSPC) for WBTs was approved in December 2006 and adopted in July 2007. The overarching aim of the PSPC is to improve the standards of WBT coatings and application in new builds, and in the process, achieve a 15 year target life for those coatings. The PSPC has lead to a greater need to focus on identifying suitable coating products and consideration of whether current structural designs are actually capable of being coated efficiently and reliably. However it is also very clear that the PSPC identifies that it is not only the coating performance that is an issue and that the coating performance is not only linked to the surface preparation and application process but also to the design of the structure to be coated. The PSPC highlights this design issue in section 3.3.2, states that: the coating performance can be improved by adopting measures at the ship design stage such as reducing scallops, using rolled profiles, avoiding complex geometric configurations and ensuring that the structural configuration permits easy access for tools and to facilitate cleaning, drainage and drying of the spaces to be coated. The link to ships safety is achieved by the inclusion of the PSPC into the International Convention for the Safety Of Life At Sea (SOLAS). The SOLAS Convention in its successive forms is generally regarded as the most important of all international treaties concerning the safety of merchant ships [4]. The implication for new-builds is that a vessels design must in part take into account the needs to coat the ballast tanks and to make that process more coating friendly. The key issues limiting the achievement of good coating application are those of access and complexity. The limited access in poorly designed ballast tanks (both large and small) often make it virtually impossible for a skilled worker to achieve the required surface preparation and painting standards. Often the access and complexity issues result in inferior surface preparation standards being achieved in these areas and either an excess or a lack of coating thickness being achieved. These three key failures result in premature coating breakdown and this is often compounded by the fact that these areas are also hard to inspect and thus the risk of coating failure is compounded. So despite the fact that the PSPC having a prescriptive regime with regards to the testing, approval, selection, surface preparation, coating, inspection and data collection, the design of the space to be coated could prevent all these
safeguards from successfully enabling the coating to reach its target 15 year life. 3. COATING FAILURES The majority of coating failures are generally attributed to the process of coating as indicated in Figure 1. % of failures Figure 1: Major Causes of Coating Failures [5] In general these failures are usually attributed to inadequate surface preparation and paint application. The chart shows the typical number of failures against the cause of failure as observed by Safinah; it does not take into account the cost or value of the failure. This would suggest that the current designs are adequate, and as such effort should be focused on improving the process. This is how the PSPC seeks to achieve the 15 year target life. The critical questions are: 50 40 30 20 10 0 Which failure types result in the highest costs? Why did the process fail to provide the quality of finish required? Is it that the operators could not gain the required access to the surfaces? Did the area contain an excessive amount of edges and welds? To address these questions, it is proposed that the design of the structure has a significant effect on the successful execution of the physical activities of coating process, ultimately resulting in premature coating failures. In fact therefore it is poor structural design that is the root cause of failures in surface preparation and paint application. Once a design feature is constructed it will be there for the life of the vessel, thus contributing to the through life maintenance costs also. The reason behind reaching this conclusion is that the processes of surface preparation and coating application are well understood and have been in existence in their present form for the last 50 years. Indeed the coatings although have changed in composition are still liquid paints and also have not appreciably changed over that time. The fact that failures result is because they are being often asked to perform outside their capability limits [6] If the design of WBT structures could be simplified, while still meeting operational and production requirements, it may be possible to provide significant benefits, such as; reduction in the cost of coating ships, improved through life performance and possible routes to automation of the coating process. Typically the coating process requires between 12-25% of the total man-hours for the construction of the complete vessel, depending on vessel and yard type [7]. Coating rework can account for as much as 30% of the total coating man hours, it can be seen that if the rework and thus the overall coating work content can be reduced, then the first cost of a vessel can be significantly lowered [8]. In addition to this if the structural design is simpler then the number of coating failures should also reduce thus giving through life benefits to the ship owners. As discussed in the next section, naval architects have long been accustomed to designing vessels to meet these requirements. However the concept of design to improve the performance of coatings is a novel approach, in fact there is often a tendency to create corrosion problems as a by-product of designing to meet other requirements, for example: Complex geometries that are difficult to prepare and paint using current technology; Spaces that are difficult to access, ventilate and de-humidify; Spaces that are subsequently difficult to repair and maintain; Use of dissimilar metals; Poor placement of outfit items resulting in corrosion traps; Poor drainage plans and design detail. Thus for the first time regulations establish a formal link between the design and corrosion of ballast tanks on board ships. If tank designs are critically assessed from an ease of coating perspective then applicators and paint chemists should be surprised that there are not more coating failures in service.
4. VESSEL DESIGN The presence of water ballast tanks is required for the stability and safe navigation of the vessel when no cargo is carried, or in the case of volume restricted ships, such as container vessels and cruise ships, they are used to trim the vessel to maintain and even keel. Ship design criteria are often driven by two key operational criteria: - Cargo capacity - Speed From the ship owner s perspective, there is a requirement to carry a particular amount of cargo to make a voyage economically viable and to do this at a speed that is usually directly linked to the value of the cargo being carried. As many trade routes tend to be uni-directional, then a ballast voyage or a part ballast voyage is an eventuality that all owners have to deal with. To this end ships are designed to optimise cargo carriage at a specific speed and it is this design solution that the owner buys when purchasing a new build. Thus the concept of Design for Operation has long been a part of the ship design process. Of course the design must comply with safety and structural rules and regulations as laid down in Class rules. In many cases the design authority is the shipyard where the vessel will be built and to that end the shipyard designers will include standards that make a design a good fit to the yards production capabilities (in particular for steel work). This concept known as Design for Production and has been in existence in steel ships in many guises from the Doxford turret ships to the Liberty ships. However in more recent times it was the Swedish shipbuilding industry and the Japanese industry that mastered this approach in the late 1960 s and early 1970 s [9] [10]. At the simplest level design for production means for example that the vessel design should be optimised to be compatible with the production capability of the yard and hence reducing the total man-hours required to build, while maximising the opportunity for automation. There is no doubt that the majority of Design for Production developments have taken place in refining the steelwork aspects this is epitomised by with the introduction of flat panel lines and 3-D assembly lines, many of which have a degree of automation and even robotisation for assembly and fabrication work. While outfit work (in particular coating activities) have lagged behind in such developments [11], [12]. At the simplest level, if the size of plate that can be used to build a ship can be increased say from 3m x 12m to 4m x 16m, then less welding joins would be required to build the shell of the structure. Thus the benefits of Design for Production have long been understood and practised. Of course meeting the needs of Design for Operation and Design for Production results in compromises. Often the easiest to build design may incur penalties in the form of increased steel weight and result in reduced cargo carriage capability or an increase in power to achieve a required speed. In general these compromises are often resolved in favour of the operational requirements of the owner, resulting in more complex designs and the associated increase in maintenance costs through life. 5. DESIGN FOR COATING Design for Coating must therefore not ignore the requirements of Design for Operation or Design for Production, but build on them to further optimise the design of the vessel with a view of enabling the operational requirements to be met while improving productivity in the yard by further reduction in total man-hours to build the vessel and achieve a reduction in through life maintenance costs. Some early studies have shown that total areas to be coated on a standard vessel that employs more radical design philosophies could result in the vessel having 20-30% less area to coat. This in turn can offer shipyard considerable cost savings and productivity gains [13]. Of course the industry is a long way from achieving these 30% gains, but design method evolution could certainly move in that direction. Complexity in the structural design of a vessel can be best reflected in the following descriptors: 1. The simplest structure is a flat panel of moderate size, placed at a comfortable working height in a temperate well lit and ventilated environment, it is likely that an averagely skilled worker would achieve a high quality of coating finish. As a result of this the probability of an in-service coating failure during the predicted life of the coating is much reduced.
2. At the next level of complexity, the ships outer hull plating is made up of many such flat panels however they are not situated at comfortable working heights in controllable environments and in many cases require staging for access. This increases the complexity of the coating process and may lead to a reduction in the quality of the surface finish. 3. The cargo tanks or holds of vessels, especially in the chemical trade, are where the payload is carried and as such are the revenue generating portions of the vessel and are therefore afforded a significant amount of maintenance and repair. The difficulty in coating these areas is more an issue of access rather than structural complexity, as structural elements are located outside these spaces to maximise cargo capacity. 4. The areas of the vessel with the greatest complexity and with restricted access tend to be, the fore and aft peak tanks, the double bottom structure and any double hull structure. It is in these areas in which ballast water is carried and presents the most aggressive corrosion environment. The importance of good design practice can be quantified as follows. Any coating has the best chance to perform through life as a result of a proper first-time application with minimum subsequent repair and touch up. The cost of asset protection is normally driven by the new build project team budget, whose objectives are often at odds with the needs of through life operational costs (for a wide variety of commercial/practical reasons). In simple terms for every $1 per square metres spent on surface preparation and coating application, analysis shows that to undertake any subsequent coating repairs as a result of coating failures the cost is up to $10 per square metres to repair. Thus a slight increase in new build budget could afford significant benefits to owners [14]. Thus for the operator attention to improved design will provide benefit in enhanced through life performance and reduced through life costs. 6. DESIGN GUIDELINES There is an International Standards Organisation (ISO) standard that provides some basic design considerations. The ISO 12944 deals with Paints and varnishes Corrosion protection of steel structure by protective paint systems ; it is made up of eight sections, of most interest in this context is: Part 3 Design considerations; ISO 12944-3 notes how the design of a structure should be carried out in such a way as to facilitate surface preparation, painting inspection and maintenance. It also considers how the shape of a structure can influence its susceptibility to corrode, and recommends that the complexity of a structure should be kept to minimum. The standard also shows examples of good working practice in terms of rounding edges, spacing between stiffeners and use of corrosion resistant materials or the use of a corrosion allowance. A set of minimum required distances are presented which will allow adequate accessibility for the tools required for corrosion protection work. This standard is further supported by more informal publications such as the UK based Marine Painting Forum [15]. The information contained within this type of guide is primarily aimed at the prevention of corrosion to detail design items such as bulwarks and stanchions. It highlights how in-service ship husbandry can be reduced at the design and build stage, by closer attention to detailed design. Other studies [16] show how poor the feedback loop from in service data to new designs is, driven by the fact that often the shipyard design team have little or no feedback of how a vessel performed beyond the 12-month guarantee survey. 7. ASSESSING COMPLEXITY In order to gain a level of control of the coating process a measure of complexity for a given structure must first be established (a coating friendly index). This index may be based upon a variety of parameters such as: weld length edge length surface area per cubic meter, degree of shadowing within a given space. Any such index if used during the initial design stage would give a designer an indication of the level of intricacy of a given structure. A threshold value could be proposed, such that above which it becomes increasingly difficult for an operator to deliver a good standard of coating [17]. If consideration is given to the coating process during design, it may then be possible to reduce the overall work content by reducing the amount of rework in the coating process. If this is supported by improvements in the management systems, it should then be possible develop a sustainable and
predictable process with reduced requirements on resources and time. and Muehlhan International of Germany, one of the world s best known marine painting contractors. 8. CONCLUSIONS There is a real need to develop two complimentary disciplines need to be developed: - Design for coating - Improved coating process management systems. In effect there is a need to elevate the importance of the coating process to a level that is commensurate with all the other engineering systems on board the vessel. This implies not only changes in the design process, but also the process of managing the coating process to make it an engineering discipline. The relative increase in man-hours involved in painting ships through life, requires a more robust approach than that currently adopted and the PSPC and other regulations emerging for Crude Oil Tanks as well as guidelines for Repair and maintenance of coatings will drive such changes. The net result is that the next 10 years will likely see an unprecedented level of change in how vessels are designed, coated and maintained. 9. Dedication This paper is dedicated to the memory of Dr J A Teasdale, former Senior Lecturer in Ship Production at the Department of Naval Architecture, University of Newcastle upon Tyne, whose contribution to the development of ship production technology and design for production worldwide, often goes unacknowledged and provides much of the philosophical basis for not only this work, but much of modern shipbuilding technology. 10. ACKNOWLEDGEMENTS This project has been funded within the framework of a Knowledge Transfer Partnership (KTP). KTP is a UK-wide programme funded by 18 organisations and headed by the Technology Strategy Board, a business-led, executive nondepartmental public body. The project is a collaboration with Newcastle University School of Marine Science and Technology, American Bureau of Shipping (ABS), a world leading classification society, IHC Merwede Offshore & Marine, an innovative and specialist shipbuilder in the Netherlands, Jotun Paints of Norway, one of the marine paint majors 11. REFERENCES 1. Focus on IMO, IMO and the Safety of Bulk Carriers, http://www.imo.org/includes/blastdataonly.asp/data_id %3D7987/BULK99.FIN.pdf 2. Code of Practice for the Safe Loading and Unloading of Bulk Carriers (BLU Code), approved by the MSC at its 68th session (June 1997) and adopted November 1997, resolution A.862(20).. www.imo.org 3. EMSA report, Double Hull Tankers: High Level Panel of Experts, 3 rd June 2005. 4. SOLAS Consolidated Edition 2004, International Maritime Organisation, London 2004. 5. Safinah Ltd, internal report 6. Juran J, Managerial breakthrough, Published by McGraw Hill, 1964 7. Baldwin L., (1995), Techno-Economic Assessment of New Coating Application for New-Building Marine Production PhD thesis University of Newcastle upon Tyne. 8. Kattan, M.R., Townsin, R.L., and Baldwin, L., (1994), Painting and Ship Production Interference or Integration? RINA Corrosion Conference Paper, RINA London 1994. 9. Teasdale JA, Design for Production, Newcastle University Publication. 1974. 10. E V Lewis and R O Brien, Ships, Time Life International, Life science library (1996), Time Inc. 11. Chirillo L, Product Work Breakdown Structure, Performance Improvement and productivity, NSRP, Dec 1982 12. Chirillo L, Design for Zone Outfitting, Performance Improvement and productivity, NSRP, Dec 1983 13. M A Brooking, Dr S J Kennedy, The Performance, Safety and Production Benefits of SPS Structures for Double Hull Tankers, Royal Inst naval Architects, London 2004. 14. Safinah Ltd, internal report 15. Marine Paint Forum, Guidance Information on design for Preservation and Corrosion Control for Steel Hulled Vessels, Prepared by J. Miller, BVT Surface Fleet (Vice Chairman) 2009 16. Safinah Ltd, internal report
17. Broderick D, Kattan R and Wright P (2010) Coating of ships: the design challenge, Royal Inst of Naval Architects, London March 2010. 12. AUTHORS BIOGRAPHIES Raouf M Kattan is the managing director of Safinah Ltd an independent marine coating engineering consultancy. Dr Kattan has a longstanding interest in marine coatings and has worked with all the world's leading coatings companies and headed the product development teams of a multinational company. He has a broad experience in the problems associated with the use of marine coatings and has worked in both industry and academia. He is a Chartered Engineer and Fellow of RINA as well as being Chairman of the NACE IMO Advisory Council. Safinah Ltd. The project aims to improve the design of water ballast spaces with a view to coating them. Previous to this he undertook a project on the application of longitudinal framing to short sea vessels as part of the CREATE3S project. He completed his under graduate degree at Newcastle University, after having completed a cadetship and four subsequent years of deep sea service, reaching the rank of second engineer, with P&O Nedlloyd (formally P&O Containers). He is a graduate member of RINA. Darren R Broderick is currently under taking a KTP project involving, Newcastle University and