Improvement of reliability assessment of gas pipeline using Acoustic Emission technique

Among NDE techniques for monitoring damages on pipelines in service, the Acoustic Emission (AE) technique is effective to check initiation and propagation of critical defects under stress and exposed to aggressive environment. To investigate both reliability and applicability of the AE technique to pipelines used in Oil&Gas industry, different full scale tests have been designed and performed as significant items. A pilot line (48 '' diameter and length 194m), formed from pipes made of both steels grade API 5L X80 and X100, has been buried and monitored for about 16 months by using AE technique. External defects (dent & gouge type) have been executed on each pipe. A pressure cycling test has been provided giving pressure in the range 135-150 bar for simulating gas transport operation over many years. By means of AE technique the source localization of defects and correlation between the damage growing and the acoustic transient energy have been analyzed. The growth in the crack areas has been also periodically controlled using NDT inspections (US and magnetic particles). The results provide good perspective for using AE technique as advanced methodology to improve the reliability of pipeline.