A continual program of platform inspection in the Gulf of Mexico has shown that even relatively new structures are being subjected to severe damage due to unsuspected corrosion as well as other causes. A comprehensive inspection program can discover this damage in the early stages and provide a basis for preventive maintenance. Underwater repair techniques have been developed for correction of both minor and major structural damage.
Underwater inspections of platforms in the Gulf of Mexico have been conducted on a systematic basis since 1968. Not all platforms have been inspected. Of those inspected, however, the findings define many problems which could be prevented or arrested once discovered. More operators are realizing the value of conducting regular inspections. Some of the methods and results of these inspects have been reported previously.)
Complete underwater inspections are expensive and time consuming. Information compiled during several hundred platform inspections has permitted development of more selective and sophisticated inspection procedures. To provide the maximum possible inspection coverage at minimum cost, three "phases" of inspection have evolved.
A short duration inspection of the shallow levels with only minimal inspection of the deeper levels. Marine growth is removed in a few small areas to determine whether, or not corrosion of welds or structural braces may have occurred. The inspecting divers also make a rather general inspection of the structure to determine whether any debris is lying across the braces or whether major structural damage has occurred.
A complete visual in spection of the entire structure from mudline to surface. Marine growth is removed in all major weld areas to determine that no cracking or other structural damage exists. Scour measurements are taken, anode condition is noted and a complete assessment of debris on the structures is produced risers and riser clamps are examined.
Includes all information produced by a Phase II inspection with the addition of marine growth removal from areas other than the welded joints. This type of inspection is required to determine the location of all major corrosion damage and is initiated when substantial corrosion damage is thought to exist. Marine growth is removed from most of the structure's surface area.
Phase I inspections are recommended where there is no reason to believe that structural damage has occurred due to mechanical stresses or inadequate cathodic protection. This inspection may produce evidence that further inspection is 'Warranted. For example, substantial pitting found in the few areas cleaned during a Phase I inspection usually indicates that the entire structure may well be affected. Our experience has shown that a good Phase I inspection will generally indicate if further inspection is needed. By restricting the inspection to the shallower levels of the platform, the size of the diving team, the amount of support equipment required, and the cost of the inspection can be kept at a minimum.
