Early Coating Failures on Offshore Platforms
by James N. Britton (2004)
This paper describes several common modes of early coating failure that lead to corrosion problems on offshore platforms. Symptoms are analyzed, and solutions are presented. The work is based on the examination of two offshore platforms in the Gulf of Mexico that had been in service for less than 18 months.
This paper provides some examples of how offshore paint systems in atmospheric service fail to deliver protection for their full life expectancy. For this study, we have selected two typical fixed drilling/production platforms in the Gulf of Mexico as case histories. Both deck facilities were fabricated on the US Gulf Coast at different fabrication yards. The jackets and decks were actually set in place in June of 1997. Our investigation was performed in November of 1998; the facilities had been offshore for only 17 months at the time of inspection.
Why Did Failures Occur?
Analysis of the following examples will show six basic reasons for the poor performance of coatings. Some are easy to deal with and others require much more effort to repair. Often it is one or more of these causes working together to produce the end result. In each example I have attempted to propose a solution that is workable.
The six causes are as follows:
1. Poor surface preparation (especially surface cleanliness).
2. Poor coating application.
3. Poor or inadequate inspection.
4. Poor specifications (both construction and coating).
5. Poor component design.
6. Murphy's Law
Failure 1: Beam Edges
Figure 1. illustrates a problem that was found in many locations on the structure, in particular where plate gussets had been welded to I-Beams. The sharp edges of the plate sections are particularly difficult to coat. They should have been radiused,which would have facilitated a better application of the coating. However this is not the full extent, nor is it the single cause of the problem;
Inadequate film thickness is a basic problem that is clearly not given enough attention by inspectors, although one would expect applicators to understand the requirements. The specifications call for a stripe coat that was obviously not applied. This failure will progress rapidly, undercutting will soon fail the system (2-3 Years) to the point that an expensive re-paint will be required.
1. Select coatings with improved edge retention characteristics.
2. Ensure the correct application of stripe coats at the beam edges (as recommended by the paint manufacturer).
3. Radius all beam edges to improve retention characteristics.