Offshore Cranes for the Petroleum Industry
An offshore crane is defined as a pedestal-mounted elevating and rotating lifting device used to transfer materials or personnel to or from marine vessels, barges and structures, according to API Spec 2C, a set of standards used to manufacture marine cranes. These marine applications include bottom-supported, floating platform and ship-hulled vessels used in production and drilling operations, shipboard applications and heavy-lift applications.
The offshore oil and gas industry was established in 1954 with the first fixed platform installed near Morgan City, Louisiana in the Gulf of Mexico. The only cranes available for use on these early platforms were existing land-based construction machines. Unlike these cranes, though, offshore cranes are fixed structures incapable of moving with their loads. However, customers often make inquiries along the lines of, "We need a 100-ton crane". The next question becomes, "What is the customer's definition of a 100-ton crane?"
A crane's capacity depends on multiple factors a purchaser must supply to its crane manufacturer. These include the structure upon which the crane is mounted (i.e. bottom-supported, semi-submersible, ship-hulled), the environmental conditions in the platform's location and the load's location in relation to the structure.
To assist customers in properly expressing their lifting needs, Seatrax offers the table below to describe the ratings and lifting capabilities of our offshore cranes.
All tons are short tons of 2,000 lbs. All boom lengths are in feet. All radii are in feet.
Red column: the theoretical weight that can be suspended from the boom tip with the boom lengths and radii shown without exceeding the API 2C allowable stresses for onboard lifts from a bottom-supported structure.
Blue column: the maximum weight that can be lifted with the hoists and wire ropes normally supplied for the boom lengths and radii shown in full compliance with API Specification 2C for onboard lifts from a bottom-supported structure.
Green column: the maximum weight that can be lifted in full compliance with API Specification 2C, for the boom lengths and radii shown, for offboard supply boat lifts, with a significant wave height of 7 feet and a 30-knot wind, from a bottom-supported structure. The boom foot pin elevation is assumed to be 110 feet above the water.
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