Despite all attention given to natural gas transmission pipelines, defects due to corrosion and third party activities can still be detected. These defects should be assessed and pipeline repair or replacement may be required. Gaz de France R&D Division has developed a methodology and an associated software to assess the integrity of ageing operating pipelines and to build inspection and re-inspection program: “GADline®”. The “GADline®” methodology and associated software allows: - to assess defects with deterministic and probabilistic methods. Six defect types are taken into account in the software: corrosions, gouges, grinding metal losses, dents, gouges in dents, and dents associated with grinding metal losses. For each of these defects, burst and fatigue behaviors are assessed, based on well-known criteria (BS7910, B31G and EPRG) and criteria developed by Gaz De France. All these criteria have been validated throughout tests campaigns to suit the actual behavior of the defects detected on the Gaz de France pipeline network. - to classify the defects in three categories: acceptable, temporarily acceptable or unacceptable. Thanks to the software, the acceptability results can be easily read on a defect assessment diagram and result sheets can be printed. - to analyze defects detected by in-line inspection or above ground surveys. Defect dimensions measured by pigs or after manual measurements can be used as input data, allowing more or less accurate analysis. - to prepare intervention programs. These intervention programs allow to identify the locations, where a drop in pressure is necessary to preserve the integrity of pipeline and the safety of people and environment. They also allow to identify locations, where future interventions will be necessary. Finally they facilitate the decision making process regarding re-inspection program frequency by calculating failure probability per km for each corrosion defect. (This module software is detailed in another IPC article. [1])

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