Jack-Up Rig Gear Racks

Petrosteel specializes in supplying extremely thick high strength alloy steel plates designed for gear rack applications. High strength quenched and tempered, fine grained structural steel plates with yield strength levels at or above 690 MPa (100ksi) are produced for this application. Because jack- up rigs are sometimes expected to operate in harsh and extreme environmental conditions, the gear rack alloy steel plates must also meet challenging toughness requirements from a minimum average of 34 Joules to 69 Joules in temperatures as low as -60C. The dimensional tolerances for the gear teeth are very restrictive. Meeting these tolerances is critical to successful jacking operation on the rig. A cutting mistake while producing the gear rack from plate can lead to the loss of a very expensive piece of alloy steel. The expertise for cutting the gear racks requires a great deal of developmental effort and control.

Chords

Chords are high strength alloy steel components fabricated into the shape of a half-pipe. The steel selected for chords must meet the same high strength, high toughness mechanical property requirements as specified for the gear racks. Thinner chords are produced by cold forming quenched and tempered alloy steel plate to shape while thicker chords are hot formed followed by a quench and temper heat treatment. Chords are welded to each primary surface of the gear rack in order to provided stiffness to the rack. This chord-to- rack weldment is termed a leg assembly. Assemblies are welded end to end until the total leg length is completed. Three vertical leg assemblies are connected to each other in triangular cross section with brace pipes welded to the chords. This completes the rig leg. The traditional jack up design utilizes three legs for each rig although some rigs are constructed with four legs.

Fabricated Leg Assemblies

The lowering of the legs and the elevation of the hull is made possible through a jacking system inside the legs, mainly consisting of gears and gear racks. The gear rack is the primary load bearing component of the leg. Because of the considerable weight of the rig and the environmental loads, the alloy steel from which the legs are fabricated must be very high strength with excellent toughness at low temperatures. Petrosteel specializes in supplying the main components of the leg which include gear racks, chords and brace pipes. We are also qualified to supply steel material for the hull structural parts and alloy steel plates for jack up rig cantilevers sections.

Brace Pipes

Brace pipes are produced from quenched and tempered high strength alloy steel seamless pipes. Because of the forces exerted by wind, waves and operating loads, brace pipes are needed to provide and maintain stability of the rig legs while situated on the ocean floor. Like the steel plates for the chords and gear racks the steel for those brace pipes has to meet the demands of harsh environments with yield strength levels at or greater than 450 MPa (65 ksi). With the merger of Petrosteel and Edgen Murray we are now capable of supplying brace pipes in addition to other jack up rig components including gear racks, chords and hull structural steel plates.