In Service Weld Xray Method for Thick Fittings on Large Diameter Licquid Filled Pipelines Available to Purchase

Background: Enbridge Pipelines (Lakehead) was interested in a method to analyze longitudinal butt and fillet welds on pipeline repair sleeves and stopple tee fittings with the goal of finding weld defects such as inadequate root penetration, weld porosity, slag inclusions and other structural defects. Problem: Traditional pipeline x-ray techniques to not generate enough energy to overcome steel thicknesses up to 3.6 inches (91.4 mm) and the density of crude oil in a 34 inch (863.6 mm) diameter pipe. Attempts using cobalt 60 with up to 60 minute exposures did not produce x-rays with distinguishable features. Technology Comparison: Two methods were considered. One utilized an automated array of ultrasonic probes each specifically targeting regions within the longitudinal butt weld. This method was successfully developed for butt welds, however Enbridge chose to pursue using a high power XRay source called a Linear Accelerator (Linac) to look at butt and fillet welds. Linear Accelerator Technical Description: Derived from work done by the Electrical Power Research Institute (EPRI), the Linac unit has demonstrated that it can produce code quality in service inspections for power plant boilers, nuclear plant piping, pre-stressed concrete bridge sections and other applications. Its design has been adapted from the Los Alamos Science Research Center’s work with the atomic bomb program. This is the highest power portable x-ray source in the world with a total power of 6 million volts as compared with the 200,000 equivalent volts produced by a Cobalt 60 radiation source. Field Trial and Results: The test specimen was a 34 inch (863.6 mm) diameter stopple tee which had been removed from the pipeline system and filled with water. Hole type penetrameters were placed directly next to the long seam welds on the stopple tee to verify the image quality, X-Ray images were exposed in 13–15 seconds and consistently produced sensitivities of 2T on 25 & 30, which was well within code requirements for the material. This technology displayed weld defects including lack of root penetration, porosity and slag inclusion that could be interpreted to code standards. Summary: This field trial proved that the Linac could be used in actual conditions. The Linac unit would requires some minor modifications for pipeline application including special mounting brackets and other small adjustments. Public safety is also a concern with this high power source as public evacuation is required within a 250 foot (76.2 m) radius of the source. Enbridge did not undertake a larger program with this technology but demonstrated that it could be used successfully if required.