Abstract
In the offshore marine industry, a remote operated vehicle, ROV, must bring a limited supply of hydraulic oil with it to the ocean floor for operation. Industry ROVs use robotic arms to do work at the bed of the ocean. Hydraulic valves are used to direct and control the hydraulic fluid, most often oil, running through the system to move the arms as well as spin the thrusters to move the ROV around. The encompassing ocean water is impure and highly corrosive to these metallic valves. If sea water leaks into a valve it can ruin the structure and contaminate the entire hydraulic system. If oil leaks out, it reduces system pressure from the closed circuit and pollutes the wildlife habitat surrounding it.
This project proposes new materials for two different subsea valve designs that allow sea water to be used as the working fluid itself, thus eliminating the negative impacts of hydraulic oil. The material combination must be suitable together against two primary valve failure modes: corrosion and galling. Prototypes A and B are made of ductile metals and ceramics, respectively. These will be evaluated for their mechanical ability to perform in the proposed sea water environment, which is corrosive to traditional metallic valves. Ceramics are resistant to corrosion but do not have the strength of a metal. The purpose of this paper is to provide a method for evaluating suitable material combinations for a valve design that will be tested and analyzed against current sea water operated valves.
A test plan is outlined here to validate both design and material selection of a proportional, directional control valve. Prototype A is a typical 4-way, 2-position directional control valve body and spool design that will be machined out of two dissimilar metals. Table 2 provides suggested material combinations to be tested together for this model. Prototype B is a 3-way, 2-position sliding disc design proposed to be made of Yttria-stabilized zirconia and graphite. These designs can be endurance tested until failure using a brine solution as the medium including 15% particulates to simulate a real-life working environment. Each valve should have an acceptable leak rate per API 598 Valve Leakage Rates but must be tested to verify. The functionality and efficiency of the prototype valve can be graphed based on flow rate and longest overall life cycle. These designs can then be compared to an industry standard oil-based valve tested in the same conditions.