Experimental observation of creep damage evolution in seam-welded elbows of mod. 9Cr-1Mo steel

Creep damage analysis of simulated-HAZ notched bar specimens of modified 9Cr-1Mo steel

“…According to the microscopic observation of cavity initiation in P91 FGHAZ by Masuyama et al (2013), small sub-micron cavities initiate at triple points or precipitates at the boundaries of FGHAZ grains; these cavities grow and link to completely surround a grain and thus create cavities with the size of the FGHAZ grains, which subsequently coalesce with neighboring grain-size cavities, leading to the formation of microcracks. The number density of grain-size cavities (cavity density, for brevity) is usually used as a measure of creep damage in P91 welded joints (Fukahori et al, 2013, Komai, et al, 2016. Nondestructive inspection of the Takashi HONDA*, Takuya FUKAHORI*, Toshihide IGARI*, Yasuharu CHUMAN*, Takumi TOKIYOSHI* and Alan CF COCKS** surface and subsurface of pipe welds is carried out to examine the current damage, such as the cavity density, and the results are employed to guide simulation-based predictions.…”

Creep damage analysis of mod.9Cr-1Mo steel welds considering void mechanics modeling

“…In the reference [19], we carried out a simulation based on random-fracture-resistance model of grain boundaries to predict time-history of creep void density distribution in mod.9Cr-1Mo steel welds. We compared the obtained results with observed results [11] for through-thickness distribution of voids and cracks, in which FGHAZ in the other side of ruptured FGHAZ was observed. In some area in the thickness, micro cracks are observed, and the simulated results of creep void density at this area was about 4000/mm 2 .…”

“…They then surround the grain, resulting in the formation of defects (voids) of the order of the grain size, which connect with adjacent defects (voids), to form micro-cracks. The increase in the number density of grain size defects (voids) is used as an index of actual creep damage [11].…”

“…Outline of Experimental Results for Welded Joints.3.1 Uniaxial creep tests for large cross weld specimensKomai et al[11] conducted creep tests at 650ºC under a stress of 66 MPa on modified 9Cr-1Mo steel specimens (extracted from a plate) of rectangular cross section 42 mm wide by 32 mm thick, with X-and U-grooves. The rupture time and the cross section after rupture of each specimen are shown in Fig.4.…”

Type IV creep crack initiation and propagation in mod.9Cr-1Mo steel welds

“…They then surround the grain, resulting in the formation of defects (voids) of the order of the grain size, which connect with adjacent defects (voids), to form micro-cracks. The increase in the number density of grain size defects (voids) is used as an index of actual creep damage [7]. A damage-mechanics approach [8][9][10][11] seems to be appropriate for simulating the failure process from microscopic damage of the FGHAZ to final fracture of a welded joint.…”