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.

A pipeline laid directly on the seafloor experiences boundary layer effects of waves and current-dominated flows close to the seabed in shallow and intermediate waters. Type of seabed soil plays a vital role in changing as-installed condition of pipeline throughout its lifespan. Hydrocarbon fields located in the immediate vicinity of shores on the west coast of the Indian peninsula experience some of the world's most severe seabed currents. The seabed soil in these offshore regions is primarily fine loose sand with great potential for liquefaction. Due to a combination of strong underwater currents and moving soil sediments, the seabed is considerably mobile and poses a great challenge to pipeline engineers in designing subsea facilities that can withstand underwater scouring. The remedial measures for scour protection have a vital role in the feasibility of a project if the field is marginal. It also affects the installation schedule to a greater extent considering a vey narrow weather window. This paper details the methodology used for optimum design and safe installation of a subsea pipeline-riser system along with permanent scour protection supports with minimal impact on installation costs and project completion schedule. Project OverviewExploratory efforts carried out in the field have resulted in a gas discovery in prospect A in the block. The field is comparatively marginal producing 2.4 million standard cubic meters per day of gas containing more than 98% methane with no CO 2 and H 2 S. The field development involves installation of 2 unmanned wellhead platforms located in water depths of 25m and associated submarine pipelines. Gas from these platforms will be gathered on an existing wellhead platform by 18" rigid pipelines. For hook-up of this pipeline major modification works have also been planned at the existing platform which is located at a distance of 30km from the coastal town of Suvali. The gathered gas will be transferred to an onshore processing facility via an existing 24" submarine pipeline. The operator planned to develop the field on a fast track with the target of start of commercial production by the last quarter of 2011. Geographical LocationThe hydrocarbon field is located in the Gulf of Khambhat, (also called the Gulf of Cambay) about 250 km North West from the city of Mumbai, India and around 35-40 kms from the shoreline. As shown in Figure 1 Gulf of Khambhat is trumpetshaped gulf of the Arabian Sea, indenting northward the coast of Gujarat state in western India, between the city of Mumbai and the Kathiawad region of Gujarat. The gulf is 200km wide at its mouth between Diu and Daman, but rapidly narrows to 25km. It receives many rivers, including the Sabarmati and Narmada (Ref. 1) in the same region. In the subtropical regions of the Indian subcontinent the direction of the wind is from South West during the monsoon season lasting from June to September. The shape of the Gulf of Khambhat and its orientation contributes to a high tidal range in order of 12m and a high velocity of ent...

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.

Long span Flare Booms are fatigue sensitive. Most of these Flares are also protected by the passive fire insulation and hence inspection of Flare structural joints for signs of fatigue cracking/damage during it's service life can result in high maintenance cost. Fatigue design is governed by selected wind speeds also called as wind blocks. It is also governed by the shape of the wind load spectrum. These two parameters viz wind speeds and wind load spectrum play a vital role influencing fatigue life. Present paper contains methodology for selection of the wind blocks. Selection of the directional dependent input parameters to a wind load spectrum is also discussed. Both these cases are studied independently to get the insight on the fatigue life impact. Ultimate aim is to ensure adequate/sufficient fatigue design life of the Flare with minimum maintenance cost.