Offshore WTG Monopile Installation – Crane Vessel Preparation

Abstract

Abstract Oil and Gas EPC contractors in the Middle East are gradually transitioning into the Wind farm development projects in Far East Asia and Europe. NPCC, one of the leading contractors in the EPC of fixed oil and gas platforms in Middle East is executing the installation of Wind turbine generator (WTG) monopile foundations in an offshore field of Northeast Asia. Monopiles are simple type of structural foundation used to support the wind turbines in offshore fields and are designed to withstand the operational and environmental loads on the latter. A simple and common form of WTG foundation would be a single vertical monopile which differs from conventional offshore jacket piles with respect to its large diameter (8 meter) and weight (up to 1,950mt) based on the capacity of WTG. Installation of these piles requires specialized custom-made equipment for lifting, upending and standalone vertical driving. The foundations of fixed platforms typically consist of a jacket with a mud mat and drilled/driven grouted piles with a maximum diameter of 2.5 meters. These piles are crucial for supporting the process platforms or wellhead topsides. The conventional installation method involves transporting the jacket and piles on a cargo barge and installing them using a simple, dual block lifting system with or without upending clamps on the barge. However, when dealing with large diameter monopiles, the transport barge can only accommodate two of them. At offshore, these monopiles must be shifted to either a separate barge or a crane vessel equipped with a massive upending hinge for upending prior to installation / driving at final location. The installation aids used for wind farm foundation components are completely different and unique from those used for installing foundations of fixed oil and gas platforms. Unlike fixed jacket foundations where the jacket legs guide the pile installation and driving process, monopiles require a gripping system to hold them vertically in place during installation. Such equipment necessitates careful consideration for layout onboard, and this paper explores the challenges involved in modifying the crane vessel layout to accommodate WTG monopile installation. Transforming an existing derrick lay floating crane vessel for WTG monopile installation is a highly challenging and critical task. This paper delves into various aspects to be considered when converting a floating vessel to make it suitable for foundation installations on Offshore Wind Farms. The paper extensively covers topics related to Constructability, Mobilization, and Installation, offering valuable insights for the installation engineering of monopiles. Moreover, it serves as a valuable reference for any Installation Contractor venturing into wind farm installations.