Ships operate in a severely corroding and (metal) fatiguing environment that reduces the strength of the ship structure, which can only be kept safe by regular inspection and repair of paint coatings, excessively corroded plate and fatigue cracks.
Present inspection planning, and feedback on design, is based on long term experience with usually no account taken of the needs of any specific ship. Reliability or Risk-based methods, applied in other industries, are not applicable to this problem of using information from large numbers of ships to improve the inspection planning of any given ship.
Structural failures of ships are, relative to onshore structures, very common and these contribute to the personal risk levels of mariners, and contribute to high pollution and economic costs.
The primary objective of the RISPECT project is to use ship structural inspection results (coating condition, corrosion, cracks and deformation) along with the calculated expected results to guide future inspections required to achieve a minimum structural reliability. This probabilistic inspection planning is not new but this project takes the method a stage further to use data from large numbers of ships in a central statistical database to contribute to the decision making process for any one ship. This has the effect of combining the traditional Classification Society broad view with the usual probabilistic method that is based on data from one ship only. Secondary objectives of the project are to:
- improve communications between ship owners, managers, inspectors and class;
- use the results as input to new design.
This project's methodology has evolved partly from a recognition that integrating two apparently different methods for inspection planning should allow better decisions to be made:
- Inspection, timing, method and feedback to design for ships has traditionally been based on experience and is essentially determined by class rules and allows them to be improved. The resulting inspection programs are usually the same for all types of ships. Exceptionally, if severe problems are found, more inspection may be demanded by the classification society for the particular ship and any sister ships. The traditional method has the advantage that it is based on an overview of ship related structural problems but cannot deal well with ship to ship variations in construction or use.
- Very occasionally, first principles, reliability based, methods have also been used to determine ship reliability and the required inspection levels and even more rarely, the initial design requirements. These methods have generally been applied to individual component parts of individual ships and can deal reasonably well with the individual part but they do not give a good estimate of the overall reliability of the ship and, crucially, they lack the large personal awareness 'experience database' that the traditional, experience-based, methodology uses, so the reliability methods are not calibrated by reality.
The project brought these two methods together and set out to develop and demonstrate an improved decision making method.
This project brought two methods together and developed and demonstrated an improved decision making method, based on a combination of experience-based and first-principles, statistical analysis, for safe, cost-effective structural inspection, repair and design rule improvement of existing ships.
Within the proposed primary methodology the experience base is handled statistically but, in parallel, the classification society experience is also tapped, using an expert system approach, to provide a 'common-sense' check on the purely statistical analysis and warn users of possible shortcomings in the method's predictions. This contributes to improved justification of important decisions, better inspections, more important defects being found and repaired, better initial design, fewer pollution incidents and the saving of lives.
In addition the project provides better interfaces between ship manager, owner, class, regulatory authority and repair yard which improves the efficiency of structural data management and (selective) distribution.
- An efficient and integrated mobility system:
- Secure Transport
- Acting on transport safety: saving thousands of lives
- Innovating for the future (technology and behaviour)
- Promoting more sustainable development