Stress-oriented protection
There are a number of reasons for coating failures although not all of them are equally harmful. Corrosion of a stringer web plate or a wash bulkhead could perhaps be treated quite differently from that of corrosion damage to a high-strength member or a pitted tank floor.
Corroded and highly-stressed structural parts subject to fatigue or stress reversals may need to be safeguarded by taking urgent protective action. Pitting of any perimeter surface is naturally also a matter of prime concern.
Corrosion of steel that is of lesser structural importance may often be judged in relation to the class “compartment minimum thickness” rather than other criteria. This is often the most dominant area in a tank.
We assist the owner in the application of our SOP = STRESS-ORIENTED PROTECTION system. The aim is to reduce the areas to be dealt with significantly. This in turn results in greater potential to reduce the owner’s costs.
The procedure involves:
- A study of the stress picture (stress level, degree of stress reversals, fatigue etc.) in order to identify potential risk areas. Usually this is best done by arrangement with the head office of the Classification Society concerned.
- A study of past crack and corrosion history.
- Making an on board tank inspection with the above points in mind and marking off/listing areas that require attention. Individual areas could be very small, such as the toe areas of some typical brackets or web notches. Large “passive” areas may be left unattended when they are compatible with the intended life span.
- Premator will suggest a practical way of carrying out corrective measures, preferably by means of a limited voyage team. The concept is to complete each small area once and for all, avoiding any problems should ballast filling become necessary during the voyage.
- The owner’s superintendent should be involved in all the phases described above. Premator will suggest a coating system that is compatible with the existing coating and which:
- has a minimum risk of under-corrosion
- lends itself to rapid curing
- offers a good level of flexibility (particularly for parts subject to high stress) The end result will be a tank protected for its intended life span at a much lower cost than that of a full recoating.
