The objective of this project is to develop and demonstrate a permanent plastic pipe repair sleeve: a simple, mechanical device that can be installed on damaged four-inch polyethylene (PE) natural gas pipe under system operating pressure. Researchers will design, construct, and demonstrate the repair fitting on an operating natural gas distribution pipeline, ensuring that the newly developed fitting meets current standards and codes.
Gas Technology Institute (GTI) – project management and research product
R.W. Lyall and Company – development and commercialization assistance
Des Plaines, Illinois 60018
When a steel pipe is gouged or is ruptured, it is not uncommon for a welder to repair the damaged pipe by welding a steel repair sleeve or full-encirclement fitting over the compromised area. However, with polyethylene (PE) plastic pipe there are no fittings currently available to duplicate this process for carrying out a permanent repair. This project is designed to develop a simple, mechanical sleeve device that can be installed on a four-inch PE pipe under pressure.
As a precursor to this project, Gas Technology Institute (GTI) has carried out analytical modeling, using conservative approximations, to ensure that a repair fitting, once installed, can effectively mitigate slow crack growth. Assuming worst-case conditions (i.e., a crack that is significantly long, sharp, and deep), model results demonstrate that the crack has a greater propensity to grow “through-wall” versus in the axial direction beneath the constraints of the end seals on the repair fitting. This is beneficial in that if defects/gouges/cracks within the boundaries of the end seals eventually breach through the wall under the influence of both longitudinal stress and hoop stress, the stresses will be equalized on both the inside of the pipe and the annular space within the mechanical repair fitting, effectively removing the driving force necessary for the crack to grow.
At the onset of the program the following product definition was established:
The mechanical repair sleeve provides an alternative to complete pipe replacement, with the added benefit of completing the pipe repair without shutting down gas service to customers. This repair option will improve the operational flexibility of distribution companies and reduce costs.
The objective of this program was to develop a plastic pipe mechanical repair fitting that can be installed on damaged 4” polyethylene (PE) pipe under system operating pressure. R.W. Lyall - the manufacturing partner – under the direction of a GTI lead collaborative group, undertook an iterative design process to develop a permanent mechanical repair fitting. Several concepts were modeled and produced using rapid prototyping technologies, and functional prototypes were built and tested. A finite element model was created to ascertain the overall system stress between the fitting halves and its clamping structure under anticipated operating conditions. The model was created in SolidWorks and the static analysis was preformed with CosmosWorks utilizing a solid mesh and the FEEPLUS solver. A best-case design concept for the mechanical repair fitting was finalized.
In essence, the mechanical repair fitting design consists of two half-circular cylindrical parts that are hinged together. After they have encircled a pipe segment that has been damaged, these two parts can be mechanically fastened to each other to contain the damage. The fitting is maintained in position by compressive forces between the elastomeric seal and the damaged pipe induced through tightening the bolts sufficiently that pressure is transmitted through compressed elastomeric rings at the ends of the sleeve. As these rings are the only portion of the sleeve that actually contact the pipe, there is an annular cavity between the inner wall of the fitting sleeve and the outer wall of the damaged portion of the pipe that is contained within the fitting body.
Because the mechanical repair fitting is intended to cope with the entire range of damage that can occur in service, the principal design challenge was the repair of a “blowing” failure; i.e., a through wall opening in the pipe wall through which pressurized gas escapes. Thus, the unique feature of the mechanical repair fitting incorporates three axially aligned holes that allow gas to escape during the repair procedure.
Following the successful design of the fitting, prototyped assembles were constructed and subjected to comprehensive testing under laboratory controlled conditions to determine the specific performance characteristics of the mechanical repair fitting. The fitting in its present state has not yet passed all of the qualification testing; nevertheless, the results of the testing demonstrate that the fitting is a viable repair option. Cumulatively, the overall results of the program have established the fundamental groundwork related to the design and development of a permanent plastic mechanical repair fitting for use on damaged PE gas mains in a safe and cost effective manner.
Current Status and Remaining Tasks:
All design, fabrication and testing has been completed.
Final Report [PDF-1.74MB] - December, 2005
Status Assessment [PDF-157KB]
“Mechanical Repair Sleeve for Plastic Pipe”, Greg Goble, R.W. Lyall & Co.; Hitesh Patadia, Richard Esposito, and Jennifer Fox, Gas Technology Institute, Proceedings of “Natural Gas Technologies 2005”, Orlando, FL, January 30 – February 2, 2005.