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

Location:
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:

• Damage to the pipeline system and surrounding environment
• Risk of fire or explosion
• Risk to human personnel
• Interrupted service
• Significant financial costs.

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:

• Improve the reliability and safety of plastic pipe systems for natural gas distribution.
• Minimize the cost and need for expensive destructive quality assurance (QA) tests.
• Increase the confidence in the use of plastics for pipes in safety critical applications or where the cost of failure would be high.

• Completed a research management plan and an assessment of the status of current technology.
• Validated the Weld Zone Inspection Method (WZIM) for plastic natural gas pipe through the use of short-term destructive mechanical tests on plastic pipe joints.
• Initiated the validation of the WZIM non-destructive inspection procedure and optimization of inspection system parameters (power output, heating time, and distance).
• Identified the most commonly used plastic pipe materials and sizes used by gas distribution companies.
• Developed weld zone images of standard joints and joints with typical defects.
• Demonstrated preliminary capability of the system to accurately detected joints with reduced strength. Initial indication is that the WZIM inspection is more sensitive than the short term destructive tests for determination of joint quality.
• Initiated testing to verify the sensitivity of the nondestructive inspection results and the STDT through long-term elevated temperature creep rupture destructive testing (LTDT) on specimens cut from selected welds.
• Updated User Requirements Document as system performance details were established.
• Procured all hardware, developed the software and performed system integration for non-destructive laser based plastic pipe inspection system and associated software, which can assign a pass/fail rating to the inspected joint based on data collected from the laser scan of the weld area.
• Wrote software program to acquire data from the laser sensor and package the data into a standard file format.
• Integrated the inspection system hardware and software, calibrated and extensively tested the system using pipe joints provided by gas distribution companies.
• Initiated development of the field test program.
• Completed field test plan.
• Field tests, in cooperation with NYSEARCH during operator certification qualification, were completed, integrating the new technology research with operator exposure during training.
• User Requirements Document was modified based on feedback from field testing.
• Algorithm for analyzing the laser data files and for assessing the integrity of the weld zone have been tested and refined.
• System was modified based on testing results from field testing program to optimize performance.
• Completed Field Data Analysis & Optimization of Specifications/Inspection Guidelines.

All work under this project has been completed.

$280,005

$93,000

NETL – Richard Baker (richard.baker@netl.doe.gov or 304-285-4714)
EWI – Constance Reichert (CReichert@ewri.org or 614-688-5000)

Final Report [PDF-4.38MB]