The Acoustic Emission (AE) technique allows taking under control the damage as superficial flaws (S-Flaws) occurred during service operation of remarkable zones of steel components, monitoring the initiation and the propagation of critical defects, submitted to static or variable stresses and aggressive environment exposure.

In the framework of the eni gas&power research project oriented to the development of a “AE methodology” for monitoring critical sections of gas transmission pipelines, a study has been carried out jointly with Centro Sviluppo Materiali (CSM), aimed to investigate reliability and applicability of the AE technique to steels used in the Oil&Gas industry.

Steel grades API 5L X65, X80 and X100, representative of traditional and new gas pipelines, have been selected. The project was scheduled investigating the potential of these steels to release elastic waves generated by sources of damage related to ductile or brittle fracture mechanisms.

Hydraulic tests until failure were carried out on single pipes using steel grade API 5L X65 for monitoring the growing of the damage on the tip of artificial surface notches (S-flaw), machined on the wall thickness [1]. Water was used as internal fluid and temperature effect was considered as well. The capability of the AE technique to discriminate ductile and brittle fractures, the essential information to approach an integrity assessment procedure, was achieved. This paper, respect to the previous ones [1], extends the AE methodology for monitoring pipelines supplying both oil and gas. In fact a third burst test was carried out filling the pipe by air and the results on this item are presented.

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