A Study of the Reeving Efficiency and Inertia of Drawworks

Abstract

Abstract The reeving efficiency is a measure of how effectively the drill line and sheaves transfer the drawworks power to the moving external load. The drill line is a steel wire rope having an inherent bending resistance. The internal bending friction is the dominating component of the single sheave efficiency, which is a function of line to sheave diameter ratio, the line tension force, the rope construction type, and the lubricator. The model used here is an empirical two parameter model validated by measurements. Experimental evidence found in the literature strongly suggests that the single sheave efficiency for typical sheaves and loads is around 99.8%. This is much higher than the 96% efficiency suggested by the American Petroleum Institute (2015) in their Recommended Practice 9B. The paper also discusses the inertia of the drill line and sheaves and presents general models for reeving efficiency and reeving inertia valid for both single and dual drawworks. It also discusses some of the implications of both the friction losses and the inertia effects. One is that systematic errors in the deadline-based hookload can be minimized by applying simple speed and acceleration dependent corrections. Another implication is that the downwards acceleration (or upwards retardation) of the external load must be limited to avoid hazardous situations with fast-line slack.