Design of a Mechanical Sealing Device for Robotic Water Distribution Pipe Rehabilitation

Water distribution pipe maintenance is a global concern. State-of-the-art pipe maintenance techniques approach buried water pipes and rehabilitate them from the outside. These processes are extremely labor-intensive and costly. The recent development of In-Pipe Robots (IPR) with locomotion and inspection functions provides a new possibility, which is to rehabilitate pipe defects internally. With proper design, rehabilitation with In-Pipe Robots could be more timely, efficient and effective comparing to conventional methods.

In contrast to the sturdy development of Locomotion and Inspection In-Pipe Robots (L-IPR and I-IPR), only a limited number of Rehabilitation In-Pipe Robots (R-IPR) have been proposed. One major concern that impedes the development of R-IPRs is the excessive amount of contamination generated during the corrosion removal stage and the leak repair stage of the rehabilitation process. The primary goal of this project is to design an instrument that can perform pipe rehabilitation operations and contain induced contamination. In this study, the author aims at conducting a contamination-less corrosion removal operation because this process by nature generates the most amount of contamination.

More specifically, the overall objective is broken down into three sub-tasks. The instrument features a module for each of them. First, the author proposes an electrical grinding module to remove corrosion that is grown on the pipe wall. Second, a mechanical sealing module is designed to contain the contamination generated during the corrosion removal process. Last but not least, a manipulator module is developed to manipulate and deploy the other modules simultaneously.

This paper centers on the comprehensive design of the mechanical sealing module, the primary objective for which is to create a complete enclosure on corroded pipe surfaces. Such surfaces possess two common characteristics, namely, macroscopical roughness and step foundation overhang. A hyper-elastic layer with optimized cross-sectional geometry is proposed to deal with direct contact with macroscopically-rough corrosion. The author adopts the surface power spectrum to characterize rough surfaces, the Gent and Lindley’s model to characterize the elastic element under compression and the Persson’s Contact Theorem to characterize the interaction between the elastic element and the rough substrate. The constructed analytical design space reveals a simple and interesting approach to optimize the design. Experimental analysis is conducted to verify the approach and is combined with Finite Element Analysis to identify physical limitations.

Change in pipe profile is another critical concern as the analytical design space cannot accurately depict the foundation on which the corrosion is grown. A sealing module relies only on the elastic layer could fail when the profile change is very abrupt, for example, a step change. The author proposes a cluster-spring suspension to support the elastic layer discretely and hence, localize the excessive deformation of the elastic layer that is caused by the step profile change. This paper presents several major considerations during the development of the cluster-spring suspension.

The sealing module is implemented and its effectiveness is evaluated. The experimental result indicates a significant reduction of compression load requirement (>40%) thanks to the optimized cross-section design of the elastic layer. Another set of experiments demonstrates the binary sealing function over foundation overhang provided the cluster-spring suspension.

The fully integrated instrument, containing the three modules, is deployed for a pipe cleaning operation in a corroded pipe. The sealing module allows no observable leak of contamination during the deployment and the contained contamination is collected with an external rinsing device. To the author’s knowledge, this is the first-ever contamination-less in-pipe maintenance operation. Since this instrument solves one of the most practical challenges faced by R-IPRs, the author believes in the near future the R-IPR community will grow rapidly and eventually confer a tremendous benefit to society.