Prediction of Collapse Phenomena in Pipelines Using Fiber Bragg Grating (FBG) Sensor Technology

摘要

This article discusses the application of fiber Bragg gratings (FBGs) for use as strain sensors to monitor and predict the buckling phenomena in sleeved pipes. Some sections of a pipeline are sleeved when their wall thickness is significantly reduced due to localized corrosion/erosion. The sleeve is basically adding additional thickness to the pipe to keep it in service; however, the sleeve does not stop corrosion/erosion from progressing, and the hydrogen evolution byproduct of the corrosion process will permeate the steel and be trapped in any gaps or voids that it may encounter. Obviously, the added sleeve provides in its annulus just such a small gap for hydrogen entrapment, and consequently, inward pipe buckling may occur due to the hydrogen pressure buildup. It has been observed that such buckling usually occurs directly under the "butt strap" reinforcement on the sleeve. The pipe buckling leads to serious consequences, including increased operational cost due to scrapers becoming lodged at the location of the buckling during the frequent scraping of the pipe. Over the past decade, use of a fiber optic sensor for strain measurement has become an attractive technology for integrity monitoring. The most frequently used technology involves inscribing nano-structured Bragg gratings, in the form of periodic variations of the optical refractive index, into the core of optical fibers made of glass. The Bragg grating period represents the scale length that can be influenced by external strains. The scale length can be determined using the wavelength of the light reflected in the optical fiber. Due to all these advantages, it was decided to use FBGs to monitor pipelines for potential buckling phenomena and to help in predicting its occurrence through measurements of several operational parameters.