The goal is to develop, demonstrate and validate an in situ non-destructive inspection method for butt fusion joints in plastic pipe that employs a laser-based inspection technology to digitally recognize images of pipe joints and interpret their condition in an effort to maintain the nation's natural gas infrastructure through enhanced inspection capability for polyethylene pipe to improve the overall safety and reliability of the natural gas distribution network.
Edison Welding Institute (EWI) – project management and research products
The Welding Institute – long term creep rupture testing of specimens
Columbus, OH 43221-3585
Butt fusion of polyethylene (PE) pipe has been used successfully by the gas distribution industry for applications ranging from city mains to residential service lines. While failures of PE pipe butt fusion joints are infrequent, the availability of an accurate and cost-effective non-destructive method of assessing butt-fusion joint quality in the field is important to assure pipe integrity. However, due to the technical limitations of the technology currently available for PE butt fusion inspection, the majority of gas companies rely on visual inspection to determine the integrity of a joint. Visual inspection can be useful but does not provide conclusive evidence of future performance.
The system being developed in this project will make use of laser based inspection technology that evaluates weld images based on the “weld zone inspection method” (WZIM). The WZIM is designed to develop laser based imagery of fusion joint bondline under heated conditions and automatically and digitally compare the images to a database of known faulty joint characteristics to indicate joint acceptability. The WZIM is the only method that specifically addresses “cold fusion” defects, a weak interface bond between the pipe-ends being joined that accounts for the majority of failures experienced in the field. This method can be applied to NDE of all types of PE butt fusion joints and materials.
EWI completed a project for NYSEARCH that established proof-of-concept for applying WZIM as a non-destructive test that involves removing the external weld bead, polishing the pipe surface in the area underneath the bead, and heating the polished pipe surface for a short time. Provided that the correct amount of heat is applied, a fusion line or “bondline” is revealed if the joint is not sound. The non-destructive method proposed with WZIM is not anticipated to have any detrimental effect on the performance of an in-service pipeline, but this is one of the items that shall be verified experimentally during this project.
The operational and performance requirements for a prototype Image Recognition System have been outlined. Image recognition inspection system sensors are currently being evaluated and the appropriate sensor brand and model will be purchased. Design of the system hardware has been finalized and all hardware components have been purchased and received, including motion control, slide assembly for positioning and fixturing.
Improved plastic pipe weld inspection methods with increased reliability are an attractive alternative to conventional methods, which include visual inspection, pressure testing and destructive testing. As in any pipeline application, the quality of the joints greatly affects the overall operational safety of the system. While major failures of polyethylene pipe butt fusion joints are fortunately infrequent, the consequences of a plastic gas pipeline failure can be severe and result in:
The situation is compounded by the fact that there is currently no simple, reliable, cost effective method of assessing the quality of fusion joints in the field. Current practice is to inspect plastic pipe joints by visual examination followed by pressure testing. This approach does not provide any assurance of long-term pipeline performance.
Successful implementation of the proposed innovative non-destructive in-situ inspection method will offer the following benefits:
All work under this project has been completed.
Final Report [PDF-4.38MB]