USING VIBRATION MEASUREMENTS TO ASSESS STRUCTURAL INTEGRITY

Structural vibration monitoring can aid in assessing offshore platform structural integrity. The method utilizes topside acceleration measurements to detect the platform's natural periods of vibration; the periods depend only on platform weights (mass) and resistance (stiffness). If the platform's natural period increases over time, in the absence of a change in mass, it can indicate a loss of structural integrity. The vibration survey utilizes a portable monitoring system, which includes sensitive low frequency accelerometers. The above water monitoring provides information on the below water structural integrity; the method is very low cost when compared to diver or ROV surveys. Examples of structural monitoring surveys are presented, including the following: verification that a platform remained fit for purpose despite having its foundation disturbed by a shallow gas release, two cases of using surveys to confirm jacket stiffness recovery following repairs of structural damage caused by Gulf of Mexico hurricanes and evaluation of a minimal platform after a heavy compressor was installed. The development of a natural period database is reviewed. The database, covering 95 platforms in Asian waters, was developed to reduce inspection costs and aid in life extension reviews, as well as providing quick integrity assessments should a tropical cyclone cross the production area.