Tech Briefs

A robotic inspection system enables preventative maintenance in space-constrained piping systems.

Fleet piping systems are complex, space-constrained systems that are difficult to inspect using standard external inspection techniques. Pipe lagging, as well as limited space, makes external access prohibitively expensive and difficult. A robotic tool was developed that will deliver a sensor package capable of real-time corrosion/erosion and pipe wall measurements. Implementation of this system will allow for fleet preventative maintenance (PM), ensuring that possible failures are detected and replaced before they occur.

Figure 1. The piping inspection robot assembly.

A mock piping test track was erected consisting of segments of schedule 40 PVC piping. Grippers were designed and fabricated integrating commercial off-the-shelf solenoid valves for airflow control.

The robot utilizes a flexible pneumatic cylinder that provides forward and backward motion while negotiating various bends in conjunction with the grippers (Figure 1). The prototype cylinder was tested to evaluate capability of operating in tight bends. This was accomplished by fixing each end to form a 90° bend and actuating the cylinder. Floating air manifolds deliver air to the entire robot and to each individual component. Additionally, air regulator bays control two set pressures of airflow through the entire robot. Pressure-regulated air is supplied to the various pneumatic actuating components on the robot.

Initial testing revealed the robot’s ability to successfully navigate through a 3"-diameter pipe mockup horizontally and vertically. Skids were added to the robot’s grippers, reducing the total cycle time of forward and backward linear motion. They allow the robot to move forward without causing any drag due to the bags being partially inflated. The robot successfully ran on autopilot through a straight section of pipe in both forward and reverse motions. The optimal travel speed was determined by adjusting the command cycle times. Flow rate usage vs. rate of speed was also obtained from this exercise.

Lab-grade borosilicate glass pipe was used for mock-piping 2.0 structures and testing. The glass aids in evaluating troublesome situations to clearly verify any problems in challenging pipe geometries. During testing, unrestricted expansion of the bladders decreased resultant axial force. A new X-wing design was developed to constrain bladder inflation and provide bearing surfaces during motion, and help center the module in the pipe. The X-shaped skid allows the silicone tubing of the grippers to inflate in a controlled geometry that decreases inflation/deflation times. A gripper snout was developed for both the front and rear of the robot to aid in smoother motion of the gripper around curves, tees, elbows, etc. The new design allowed for higher pressure, which allowed the gripper to achieve 30 pounds of axial force.

Figure 2. Bends increase friction as they force more of the robot into contact with the inner wall of the pipe.
Based on the success of the new X-wing design, a second set of parts was fabricated. A pod enclosure was designed to improve maneuvering capability and offers protection for the electronics against the pipe environment. The pod is attached to the aft end of the robot, which additionally serves as the connection point to the robot’s tether. The tether serves as an umbilical between the operator control station and the robot.

A pilot cone was designed to improve maneuverability through the pipe. Prior to this design, the robot had a flat manifold that impeded movement during testing. During testing, it was observed that when one gripper was active and the second gripper activated, the first gripper bladder would slightly deflate while also loosing gripping force resulting from a transient decrease in pressure. Adding check valves minimized this effect by isolating each gripper.

Two steering heads comprised of the same components were developed, the only difference being the location of the pneumatic muscles on the head. The range of motion between the two was analyzed for optimal flex/travel. The steering head consists of a tail regulator manifold that reduces the high-pressure line down to 40 psi, a solenoid valve bank for controlling each muscle individually, and a pneumatic muscle assembly allowing eight possible directions. During the manual extraction, direction changes (bends), in particular, increase friction as they force more of the robot into contact with the inner wall of the pipe (Figure 2). This friction can cause excessive stress on the tube fitting connections and wiring, which may fail if excessive pull force is used when extracting the robot. Stainless steel rope linkages were attached between the manifolds to act as a strain relief.

Another pod enclosure was designed and fabricated using 6061-T6 aluminum. The new pod is machined out of a single piece of aluminum, which makes it much more robust than the previous acrylic iteration. The new version also allows for improved wire strain relief system than the previous design.

This work was done by Karl R. Edminster of Electromechanica for the Office of Naval Research. ONR-0031