Re-analysis of allowable corrosion margins for ships in operation.

Purpose

This list is normally prepared by DNV in connection with the planning process for the third renewal survey. This re-analysis is done at the request of owners to discover if, based on current rules, corrosion margins beyond the normal percentage values may be granted.

Benefits

Based on the outcome of the analysis, a reduction in steel renewals and thus also docking time and costs may be achieved.

Features

The minimum thickness list is a description of the allowable corrosion margin for longitudinal structural elements within 0.4L amidships. There are different measures that can be considered in order to evaluate the possibility of granting reduced corrosion margins:

• The re-calculation of Rule thickness, based on current rules and procedures, either by simple rule calculations or more advanced FEM calculations. This in order to investigate if there is some built-in surplus strength in the ship.
• The deletion of class notations ( Reduction of loads on structure)
• A reduction in loading flexibility
• The reduction of the allowable still water bending moment limits (SWBM)
• Service restrictions (Reduced sea loads on structure)
• The addition of an extra stiffening structure in lieu of steel renewals

Alternative means of reinforcement may also be considered. The re-calculated t-min values must comply with the strength standards built into the normal procedure. There is no guarantee that the re-analysis will result in reduced corrosion margins.

Process

Upon request, DNV may be able to carry out a re-analysis of the minimum thickness list. The estimated time for the re-analysis ranges from a few hours to 6-8 weeks, depending on the complexity. The analysis is not considered to be beyond normal class assistance and will be invoiced based on recourses spent.

This service may be carried out upon Owner's request, but is normally not actively marketed.