PSI - Issue 66

Yamato Abiru et al. / Procedia Structural Integrity 66 (2024) 525–534 Author name / Structural Integrity Procedia 00 (2025) 000–000

533 9

Crack-free

N =4,000 ( a = 1.93 mm)

N =5,000 ( a = 2.04 mm)

N =50,000 ( a = 3.85 mm)

N =78,000 ( a = 4.0 mm: Reached outer surface of pipe)

Fig. 10. Results of hammering test for both ends supported beams of hydrogen-precharged pipe specimen. Refer to Fig. 3 for striking point A C. and to Fig. 5 for corresponding crack length in thickness direction .

Conclusion Fatigue tests were performed by applying cyclic compressive loads to the top and bottom of STKN steel piping with an inner diameter of 8 mm and an outer diameter of 14 mm. These loads induced crack propagation from the inner surface in both uncharged and highly hydrogen-precharged specimens. Hydrogen precharging was achieved by immersing the piping specimens in a 40 °C, 20 mass% ammonium thiocyanate solution. Internal cracks were subsequently investigated using ECT and HT. The results are summarized below: 1. The crack growth rate in hydrogen-precharged specimens was faster than thatin uncharged specimens, with crack initiation occurring sooner in the hydrogen-precharged material. Overall, the number of cycles required for crack initiation and propagation to the outer surface decreased by approximately one-tenth in the presence of hydrogen. 2. ECT results revealed differences in the presence of large cracks between uncharged and hydrogen-precharged materials. The eddy-current test did not yield clear results for cracks at half the wall thickness. In contrast, HT results showed that cracks were detectable in uncharged specimens when the crack length reached 0.78 mm or more, while in hydrogen-precharged specimens, cracks were detectable only at lengths of 2.04 mm or greater.