Mechanistic interpretation on acidic stress-corrosion cracking of NiCrMoV steam turbine steel

Effect of Film-Forming Amines on the Acidic Stress-Corrosion Cracking Resistance of Steam Turbine Steel

“…At these regions, cracks were observed, as shown in Figure 8c. As can be seen in Figure 9, indeed, smaller secondary cracks were present close to the main crack that were not present in the rest of the gauge length [61]. This indicates that these cracks were formed because of strain localisation around the main crack at ultimate tensile strength (UTS) and not due to subcritical cracking [68,80].…”

“…A tempered martensitic microstructure with precipitates can be observed. Details on the microstructural characterisation of this steam turbine steel can be found elsewhere [60,61]. The film-forming amine oleyl propylene diamine (OLDA) was used as FFA in adsorption experiments on the steel samples, to form a hydrophobic and protective coating [42,46,58].…”

“…Steam turbine steel was machined into tensile samples with a geometry as shown in Figure 4 and a thickness of 1.5 mm [61]. The loading direction of the tensile samples is indicated with LD, whereas the normal direction (ND) is the direction perpendicular to the top surface (ND-plane), complemented with the transverse direction (TD) for sake of orthogonality.…”

“…Details on the in situ CERT set-up as well as on the method development can be found in previous work [68,69]. Tensile specimen geometry (mm) (thickness = 1.5 mm, TD = transverse direction, LD = loading direction) [61]. Adapted from [61], with permission from Elsevier, 2020.…”

“…Metals 2020, 10, x FOR PEER REVIEW 9 of 21 cracking [68,80]. Since these cracks are only present when having a combination of high local stresses and a corrosive environment, these cracks are presumably the result of SCC [61,68,69]. When examining the fracture surface of the non-coated NiCrMoV steel tested in acidic aqueous environment by SEM, both ductile regions and more brittle zones were observed, as shown in Figure 8 [61].…”