How do we do it?

The first and most basic assessment concerns in projects like these are the overall condition of the hull and thus its residual structural strength. This implies the extent of plate corrosion, amount of damage and possible previous amount of repairs carried out. Such documentation is typically established through UTM measurements whereby parts of, or the most critical parts of the vessel, are inspected and checked out.

Life time extension

The next step involves assessment of issues specifically important for the fatigue strength of the hull structure. This implies dedicated inspection and evaluation of the extent of fatigue damage in critical structural details and connections of the
Hull.

Structural Strength

The structural strength of the vessel is related to the physical dimensions of the plating and structural members. As a result of corrosion the structural strength of the hull diminishes which means that limiting curves for acceptable hull shear and bending needs to be updated. This will typically influence the vessel loading conditions and the way in which the vessel can safely be operated at a given field. Inocean has the necessary experience and analysis tools to document these issues, utilizing UTM measurements as key input. Typically, Inocean will provide documentation of minimum plate thicknesses, and thus provide a decision basis for whether there is a need for repair/plate replacement or not.

The result

For a conversion: Through such an assessment costly repair or plate replacement will be minimized, and in some cases can be totally avoided.

For an FPSO already in operation: This type of assessment has the potential to e.g. document that plate thicknesses lower than the Classification Rule criteria can be acceptable - without violating safety criteria. It can in itself provide the required documentation to ensure that Class is maintained, and thus enable an extended life at the field, without need for docking or repairs.

The net result is money saved for the client.

Fatigue Strength

The fatigue strength and life time expectancy of the hull are to a large extent related to the geometry, properties and construction of its structural details, and the way in which the hull structure has and will be exposed to dynamic loading over time. These aspects need to be considered together in order to enable prediction of remaining fatigue life, in order to enable a decision basis where possible repair/upgrade is necessary, and where there is no need.

Inocean has the necessary experience and tools to predict fatigue life time expectancy. Typically, Inocean will provide documentation showing remaining life of critical details, their extent and location on the vessel and suggestions for possible improvements to enable a prolonged hull life. Due to the inherent uncertainty of all fatigue analyses, the combination of onsite inspection and analyses enables a differentiation between the details which in some cases cannot be left unrepaired and those which need to be focused during field operation.

What you accomplish

For a conversion: By such evaluations focus is directed to the most critical details which may, or may not, need repair or modification. At the same time it provides a basis for the establishment of a risk based inspection program.

For an FPSO already in operation: Documentation of the remaining predicted fatigue life of critical structural details provides the best possible decision basis concerning life extension. It brings confidence to decisions on if, and at what time, a docking may be required within a desired extension period, or indeed at all. Also, assessment of crack growth and possible consequences for operations can be used to document a safe continuation of operations.

The net result is a better basis for operational planning and potential huge savings for the client.

Hull assessment and life time extension verifications are always required by Client and Class. Such work is typically carried out by Inocean.
 
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