Brownfield projects whether topside modifications or underwater modifications are always challenging in Offshore Industry. New facility attachments to the existing jackets in the form of J tubes, Utility Pipes, Risers etc. require clamped connections. It involves underwater removal of marine growth and installing the new clamps on existing jacket members. The allowable span lengths of these attachments pose a challenge to Engineer. Sometimes jacket members are not available to install clamps at the required location. This leads an Engineer to take misaligned and eccentric supports to satisfy the span length requirement. In few occasions this leads to the installation of the new supporting jacket member with clamped connections. This paper presents an enhanced design concept for working out the maximum possible span lengths of these pipes considering associated vortex induced vibrations (VIV). These members are checked for VIV and VIV induced fatigue to determine spacing of the supports on jacket as one of the design criteria. This paper discusses the standard methods of the VIV check and gives a more enhanced methodology by which the spans can be increased without causing VIV excitations.

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Low frequency platforms with a natural period above 3.0 seconds are sensitive to the wave induced forces. The present paper discusses the available methods in offshore industry to carry out the Extreme Wave Analysis (also called as Dynamic Inplace Analysis). The paper also compares the results of these methods with the normal approach of amplifying the wave load using a factor called Dynamic Amplification Factor (DAF). It finally gives a threshold limit based on the platform period for the use of appropriate method of Extreme Wave Analyses.

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