The Development and Application of a Fiber Optic Inspection Device for Subsea Use
Authors: Langen M.G. , Healy G. 
Published: October 2008

The United States Navy, in conjunction with a subsea engineering firm, has initiated a program to develop a diver deployed fiber optic borescope. The underwater borescope allows the in situ inspection of areas on vessels previously inaccessible except during drydock evolutions. In order to provide proof of concept, a prototype was designed, fabricated and tested. The prototype employs standard "off the shelf" components housed in a dry, pressure compensated environment. Based on information gathered during the execution of a variety of inspection tasks, the design of a production model has been completed.

Although originally conceived to inspect shaft bearings, utilization of this tool has indicated that it can be applied to the inspection of a wide variety of areas below the water line that have been previously unreachable. Applications beyond ship husbandry also exist.

The ability to inspect the internal portions of subsea valves or pipelines may offer an attractive means for preventive maintenance and/or verification of damage or wear. The underwater borescope allows a diver to provide real time video inspection information to topside personnel, thus providing clear cut information on which to base maintenance and repair decisions.

INTRODUCTION

During the course of routine deployment of naval vessels, propulsion shaft bearings may experience wear and/or damage prior to prescribed maintenance schedules. Previously the only way to inspect these bearings was to dry dock the vessel, a procedure that is both expensive and time consuming. In order to reduce maintenance costs and limit vessel downtime the Underwater ship Husbandry Division of Naval Sea Systems Command began to investigate the development of a device capable of in situ inspection of shaft bearings. A study of methods used topside to inspect areas with similar access restrictions and space constraints determined that the best approach would be to adapt a fiber optic borescope to shallow water use. As a result of this determination a subsea engineering firm was contracted and a program established to develop an inspection system.

The first step was to obtain an overview of the current technology in order to determine concept feasibility and to establish the most efficient means (financially, as well as technically) of developing an effective inspection tool. During the analysis three approaches became apparent:custom design a borescope exclusively for subsea useutilize a modified fiber optic imaging systemProtect standard "off the shelf" components in a watertight housing and transmit video images to the surface via an umbilical. The technical risks and high costs associated with the development of a custom designed borescope eliminated the consideration of this option.

The use of a fiber optic imaging system was initially deemed attractive because it limited the amount of equipment the diver was required to transport to the inspection site. A unitized system would allow all imaging and illumination equipment to remain topside, leaving only the probe and a small monitor to be carried by the diver.