Really the assessment and evaluation of the existing offshore structures and FPSO is very complicated and need a sense from the consultant rather than theoretical calculation. Really for any old system even your body, when you are youth you can go to any doctor for medical care but when you go old you need many checks and professional doctors.
Deal with the old structure very carefully as wrong treatment may result to death?!!!
The problem for the offshore structures and marine vessels like FPSO, as they are mature now all over the world and the challenge now is how we can calculate its life time or in another meaning can we extend its life time. I want to conclude that the answer is under investigations and researches until now. The main problem is the fatigue effect as its calculations have a high uncertainty and the expected life time requires a sort of probability calculation. In general, until now the structure engineer can not precise and guarantee the life extension.
There is a relation between percentage of reduction due to corrosion and the steel plate capacity under bending moment. So it is found that reduction of 30% in thickness corresponding in reduction around 50% in the capacity and the capacity is reduced gradually until reduction 70% as in this time it shall be risky to operate in this condition, but if you reduce the load dramatically you will be in a good condition as the capacity will be reduce slowly.
Structure integrity management system can cover this issue, as it is presented in detail for the webinar session 4.1 you can register on it https://elreedyman.com/webinars/
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