Estimation of Reliability of Underwater Polymetallic Nodule Mining Machine

This paper presents the reliability analysis carried out on the subsystems of the underwater polymetallic nodule mining machine developed by National Institute of Ocean Technology, India, which is being enhanced for polymetallic nodule mining technology demonstration at 6,000-m water depth in the Central Indian Ocean Basin, where manganese nodules are available in abundance. The mining machine, which is a tracked vehicle, was successfully demonstrated at a water depth of 512 m, wherein the nodules are collected, crushed, and pumped to the mother vessel. Reliable long-term operation at 6,000 m is the key factor, as retrieval of the system to the top side for rectification is costly and time-consuming. It is identified that the reliability of the 6,000-m-rated mining machine subsystems could be improved by the use of localized control power, redundant electronics, and hydraulic systems. It is estimated that, with the suggested improvements, the probability of failure of the systems involved in vehicle maneuvering, mineral crushing, and pumping could be reduced from 91%, 88.8%, and 84.59% to 68%, 57%, and 39%, respectively, when the systems are operated for a period of 1,460 h in a year. The results serve as a guideline for 6,000-m-depth-rated mining machine system design with a trade-off on size, weight, and required level of reliability.