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Cost effective inspection and structural maintenance for ship safety and environmental protection throughout its life cycle

Final Report Summary - CAS (Cost effective inspection and structural maintenance for ship safety and environmental protection throughout its life cycle)

The main objectives of the CAS project were:
- to integrate all phases of the ship condition assessment process, achieving seamless communication between the measurements on board the ship and the use of sophisticated structural condition assessment tools.
- to build a simplified ship electronic model of the ships to be inspected. It was to be a numerical 3D model designed to collect measurements on board ships in service, then to perform all possible post-treatments from this 3D model. The 3D model was to be a neutral standard to enable exchange data between all concerned actors, mainly: Thickness Measurement Company (TMCo), Classification society and Shipowner.
- to add measurement and inspection information into the ship model. Each measurement on board would finally be associated with a specific structural element in the ship model.
- to provide the channel for integration of robots-made measurements.
- to provide a few hours after any ship's inspection a complete view of the current condition of the ship, using visualisation and virtual reality tools, thus triggering immediate requirement for repairs, instead of the weeks of delay needed with the existing process.
-to provide repair decisions and residual lifetime of the structure with modern methods of risk based maintenance modelling.
- to provide a gain in overall efficiency of ships repairs and consequently in ships safety as a consequence of the integration of the process.

It was decided that the re-engineering of the process was to include the definition of a standard exchange database, called 'Hull condition monitoring' (HCM). The HCM was to be tuned up by all the partners intervening in the process, and, as studies and tests would be performed by the partners, in the course of the project, new features would be incorporated into the standard.
The HCM design was especially focussed on:
- measurement data, corrosion, cracks and painting.
- geometrical information required for the definition of plates (planar, curved and corrugated) and profiles.
- the possibilities for the export out of a current CAD geometrical ship's model, used by the shipyards to build the ship, towards an HCM model.

The major evolutions of the HCM data model during the course of the project were:
- change from Thickness-measurement-centric to be Hull-condition-centric.
- addition of inspection results beyond thickness measurements (coating condition, cracks, etc), repair data and corrugated bulkheads.

The 3D model generators from two classification societies in the project, the 3D model generator developed in the course of the project and shipyard CAD software could successfully produce HCM files.

A strength and weakness analysis of all possible methods and available technologies for Thickness Measurements and cracks detection was carried-out. A procedure for the application of Eddy Current crack detection was provided. The standards for the inspection of corrosion prevention measures were analysed, including the inspection of coatings as well as the inspection of cathodic protection systems. Leading edge coating assessment technologies were tested.

The 'risk based inspection' (RBI) methodology adapted to HCM was developed and applied to the final demonstration. The procedure comprised a segmentation of the ship structure in areas of similar degree of risk, an estimation of the risk and an adjustment of inspection planning.

A demonstration of the CAS process in realistic conditions was performed in an European repair shipyard, on board a 150 000 DWT oil tanker, in dry dock. The ship's renewal survey measurement campaign was carried out using the CAS process and prototype tools, as developed in the project.

The demonstration proved that it was possible to build a 3D model of the whole ship, where the areas to be measured are represented with greater detail than the rest of the structure. Measurements on board consisted of measurements taken inside the ship by two UTM operators and on the outer shell by a robot. The combined measurements were entered into the HCM model and analysed using the post-processing tools developed in the project, i.e visualisation and virtual reality, condition assessment and interfaces towards class 3D model generators.

Measurements inside the ship were performed by a team of two operators:
- one operator is handling the ultrasonic probe and uses 'Rope access' to move inside the ship's tanks;
- another operator is handling the computer and is located in an equipped container on the deck of the ship.
Both operators communicate through sound headsets and a video camera, in order to define, on the HCM ship's 3D model as displayed on the screen of the computer, the location of the measurements being taken. The measurements values sent by the ultrasonic probe are automatically entered into this HCM model, each time the operator on deck touches the image of the structure on the screen of his computer. In parallel to thickness measurements, coating quality measurements were conducted using a leading edge technology.

A non-contact ultrasonic three-probe sensor was selected. Water was continuously injected to play the role of a coupling between the probes and the steel surface to be measured. The probes were mounted in a self-adhering plate equipped with magnets, and linked to the robot by a flexible sheet. A critical point was the estimation of the position of the robot in the ship. The only efficient and reliable solution found during the project was the attachment of three wires to the robot (odometry) and the continuous calculation of the position of the robot by monitoring of the length of those wires. The robot interface read the vessel HCM model generated by the 3D model generator, retrieved the positioning and measurement data in real time, displayed it in a graphical way in 3D, and updated the HCM file with this data.

Globally the project has attained its objectives: The HCM standard was published and all prototype software tools used in the condition assessment process, from the initial thickness measurement to the final assessment of the ship's structure, were developed. The project has elaborated the core conceptual principles upon which all improvements of the condition assessment process of ships in service in the next years are expected to be based.

However, some prototype tools features, although still in accordance with the project principles, were not very easy to use: for instance, the entry of thickness measurements into the 3D model was done by typing in pop-up windows. In the final demonstration, more advanced features were supplied by some pieces of software developed by partners on the sides of the project, enabling for instance the use of a touch screen to enter more conveniently the measurements into the model.

HCM applies to ordinary ships of all types, but also to FPSOs (offshore oil floating storage) and jacket type offshore platforms.
HCM is very much appropriate for connection with:
- finite element models to calculate the stress levels in the hull structure
- risk analysis modules to calculate the criticality of failures in the hull structure
- condition assessment modules, visually showing the structural elements to be repaired
- inspection/measurement robots.

A project website was developed, for use by interested general public outside the project, containing seminar and conferences presentations, press releases, the standard HCM format itself to download as well as useful related links. The address of this project website is:

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