Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 491

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s lifespan. For example, an
existing structure with a flooded member needs a comprehensive structural
study of the platform considering fatigue. A remote operating vehicle (ROV)
survey is usually used as part of API RP2A, but its requirements need to be
changed according to the location and the environmental conditions.
This case study of platform failure and the reason for its failure clarify the
pitfalls in the integrity management system philosophy and also in API RP2A
for assessment of existing structures.
The platform shown in Figure 7.16 is a well-protector platform with 4 legs
in a water depth of 39 m (130 feet). The platform was constructed in 1973 with
an inverse K bracing system. A subsea ROV survey was performed 7 years
before the failure. The survey showed 5 flooded members in the platform.
The topside facilities

Fatigue is the main factor governing a structure

weightwas27tons,with6risersand4conductors.
The deck weight was 46 tons and the jacket weight was 73 tons. The platform
was designed prior to the first edition of API RP2A; the design would have
been done to engineering company specifications, possibly supplemented by
owner recommendations.
There is no evidence that accidental loads, such as vessel impact, fatigue
load and seismic load or the effects of corrosion or marine growth were
accounted for in the design, because these were not design practice at the

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FIGURE 7.16 Platform configuration.