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Acoustic Emission Technique for Damage Assessment of Gas Pipeline in Hydraulic Test

Inspection of oil and gas pipelines for integrity assessment is usually carried out by ILI (in-line inspections) tools (pigs). In case a pipeline section cannot be inspected by pig other methods should be considered. Among these, acoustic emission is a promising NDT technique allowing monitoring of structures in service condition. As challenging task of the eni R&D project a 48” OD pilot pipeline, made up of API5L X80 steel grade pipes, has been designed and installed in CSM full scale laboratory located in Sardinia. On the outer surface of each pipe Dent & Gouge (D&G) defects have been machined, representing the Third Party Interference (TPI) damage. For about 18 months the line was operated in severe conditions in terms of cycling pressure and cathodic overprotection corresponding to a pipeline under service conditions. The nucleation and growth of cracks have been monitored by using acoustic emission (AE) technique during the campaign and supported periodically by NDT investigations. Finally, a hydraulic test was performed according to a procedure consisting of four steps characterized by increasing pressure ramps and subsequent hold time in which the pressure load has been kept. AE technique has localized and monitored the propagation of defects. In the crack areas metallographic analysis were also made.

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