Around the world, many operational gas pipelines cannot be inspected using conventional pig mounted NDT techniques. Assessment of the condition and structural integrity of such pipelines is problematic and field inspections must rely on alternative techniques and equipment. AIA (Asset Integrity Australasia - a joint venture company between UK based AESL and GTLBI) is applying a new approach to pipeline structural condition assessment based on inspection of the pipe wall, corrosion protection measures and local corrosion mechanisms and drivers. These parameters are determined by field inspections at selected locations along the pipeline. Statistical analysis techniques are applied to the definition of inspection locations and procedures, and to validate the accuracy of inspection output data. This condition assessment process was developed in the UK over a number of years, initially for application to water trunk and supply pipelines. The process has been further developed for gas transmission and distribution pipelines and gas applications for these techniques are now increasing. Field inspections of the pipeline are carried out only at selected locations, typically within small excavations, and at strategic locations, often where the pipeline crosses roads, railways, rivers and other infrastructure routes or topographical features, usually via a bridge, tunnel or other special structure. Thereafter, prediction of overall pipeline condition is derived from statistical modelling, based on recognition of typical defects, significant features of the surrounding environment and similarities within corrosion influences along the pipeline. The assessment technology is based on full pipe wall magnetic inspection using externally mounted tools. The assessment process includes further developments in techniques and equipment for assessing significant pipe coating defects from above ground, custom data recording and communication equipment and specialised data analysis techniques. Pipe coating and soil assessment procedures have been defined and are an integral part of the inspection process.
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