Study on the hydrogen induced cracking of API-X80 steels by using 3-axis controlled ultrasonic inspection unit

Three-axis controlled ultrasonic inspection unit is designed and applied to study hydrogen induced cracks (HIC) of hot rolled API-X80 steels non-destructively. The average grain size of the API-X80 is about 1.88 μm with a preferred orientation. (110) poles are preferentially oriented to normal direction (ND), (100) poles are oriented from normal direction to transverse direction (TD) for 30° and from transverse direction to rolling direction (RD) for 45°. (211) poles are oriented to transverse direction for 35°. Micro-cracks are clearly observed by the 3-axis controlled ultrasonic unit for the specimen immersed in the standard HIC solution for 24 h. Diffusive hydrogen content of the API X-80 steel after immersing for 24 h is 3.40 ± 0.03 wtppm, which dramatically increase about 160 and 170% by 4–6% pre-stain, respectively. The initiation of the HIC related to coarse inclusions like silicon and aluminum oxides.