Structure of strongly underexpanded gas jets submerged in liquids – Application to the wastage of tubes by aggressive jets

•Underexpanded gas jets submerged in liquids behave similarly to homogeneous gas jets.•The counter rotating vortex pairs of jet produce discrete imprints on the targets.•The shape of hollows made on the targets is explained by the jet structure.•The erosion–corrosion phenomenon well explains the wastage of exchange tubes. Strongly underexpanded gas jets submerged in a liquid at rest behave similarly to underexpanded homogeneous gas jets. The existence of the Taylor-Görtler vortices around the inner zone of the gas jets is demonstrated in free gas jets submerged in water by means of optical probe. In the near field, the same phenomenon produces discrete imprints, approximately distributed in a circle, when underexpanded nitrogen jet submerged in liquid sodium hydroxide and underexpanded water vapour jet submerged in liquid sodium impact onto AU4G-T4 and Incoloy 800® alloy targets respectively. For a jet-target couple, the volume of the hollow is satisfactorily related to the strain energy density of the material and the kinetic energy of the gas jet. However, the comparison between volumes of hollows produced by both jets also indicates strong corrosive action of the medium on targets. This allows better understanding of the mechanism of wastage of tubes employed in steam generators integrated in liquid metal fast breeder reactors.