Acoustic emission analysis coupled with thermogravimetric experiments dedicated to high temperature corrosion studies on metallic alloys

International audience ; High temperature corrosion of metallic alloys (like Iron, nickel, cobalt alloys) can damage equipment of many industrial domains (refinery, petrochemical …). It represents a major challenge. Acoustic emission (AE) is an interesting method owing to its sensitivity and its non-destructive aspect to quantify the level of damage in service of these alloys under various environmental conditions. High temperature corrosive phenomena create stresses in the materials; the relaxation by cracks of these stresses produces transient elastic waves which can be recorded and analyzed using the AE system. The study of these transient waves enables the anticipation of the degree of damage of the alloys. Several methods are used to record and analyze these transient elastic waves. Piezoelectric sensors fixed directly on the structure can be used. But in case of high temperature environments, a waveguide may be used to transmit waves from the sample to the sensors. Our study establishes an acoustic signals database which assigns the acoustic signals to the specific corrosion phenomena. This database will be useful for the monitoring of industrial equipment using acoustic emission methods. For this purpose, thermogravimetric analysis (TGA) has been coupled with acoustic emission (AE) devices. Simultaneous measurements of the mass variation and of the acoustic signals emitted during the corrosion of samples at high temperature provide complementary information. For this purpose a specific alumina waveguide (WG) has been developed.The oxidation of a zirconium alloy, zircaloy-4, was firstly studied using thermogravimetric experiment coupled to acoustic emission analysis to validate the waveguide operation at 900 °C. Metal dusting represents also a severe form of corrosive degradation of metal alloy. Iron metal dusting corrosion, with or without pre-oxidized layer, was studied by EA coupled with TGA at 650°C under C 4 H 10 + H 2 + He atmosphere. From these studies we can conclude that reversible mechanisms are ...