DNV
The purpose of the present Classification Notes is to provide the user with general information and a tool for
assessing the acceptance level of deterioration in hull structures
A ships original scantlings are normally based on minimum requirements according to the rules for
Classification of Ships applicable at the time of construction but may also include additions due to the initial
owners requirements or special building practices. However, there has been an extensive development in ship
design and optimization of scantlings during the last 20-30 years, and this development has in general
contributed to reduced corrosion margins. Provision of a good corrosion protection system is, therefore, now
more important than ever. As not all designs or circumstances can be covered, the instructions herein should
be used with particular caution. Acceptance of repair extent and method must be given by the Society.
The principle in this document is that general corrosion allowances will follow DNV and GL rules. This is due to differences in the existing rules where GL rules are based on a net thickness approach where the maximum general corrosion margin in service (tk) is defined in the approval stage. DNV rules do not describe the maximum corrosion allowance in service and provided the longitudinal stress level and buckling capacity is acceptable, reductions beyond the new building corrosion allowance (tk) may be accepted. However local corrosion criterias such as pitting, grooving and edge corrosion applies to both DNV and GL ships
