Allowable Contact Stresses in Jacking Gear Units Used in the Offshore Industry

摘要

An offshore jack-up drilling rig is a barge upon which a drilling platform is placed. The barge has legs that can be lowered to the sea floor to support the rig. Then the barge can be "jacked up" out of the water, providing a stable work platform from which to drill for oil and gas. Jack-up drilling rigs were first introduced in the late 1950s. Rack-and- pinion-type jack-up units were introduced soon after that and have dominated the industry ever since. The rack-and-pinion systems used to raise and lower the rig are enormous in terms of gear pitch, or module, by gear industry standards. Quarter-pitch (101.6 module) pinions are common, with both larger and smaller teeth used. The lifetime number of cycles for these units is-by gear industry standards-tiny in that rack teeth typically have 25-year lifetime cycles measured in the low hundreds. That is off the charts for AGMA (and ISO or DIN) design rules, which draw a straight line to zero cycles for contact stress cycles less than 10,000. Use of any standards was abandoned from the start in the offshore industry for jacking applications. The author presents methods via experience in that industry and suggested allowable contact stresses in such applications.