A Comparative Study of Stress Corrosion Cracking of Steam Generator Tube Materials in Water at 315 C

Investigation of Carbide Precipitation Process and Chromium Depletion during Thermal Treatment of Alloy 690

“…[16][17][18][19] Sui and co-workers studied the SCC behavior of alloys 600 and 690 in the hydrogen/steam environment; [20] they found that the cracked alloy 600 and 690 materials contained very little GB precipitation, whereas the GBs in material that did not crack were covered by continuously distributed carbide. A similar result was found by De et al, [21] who suggested that a high density of intergranular chromium carbide could improve the intergranular SCC (IGSCC) resistance in primary water and certain caustic environments; meanwhile Yun et al [22] studied the effects of laser surface melting on the intergranular corrosion of the sensitized alloy 600 and found that the precipitation of GB chromium-rich carbides could enhance the intergranular corrosion resistance of this kind of alloy. Morever, Zagal investigated the hydrogen permeation behavior in alloy 690, because the severity of the IGSCC was significantly enhanced as hydrogen evolution (i.e., under cathodic conditions) when exposed to PWR environments, [23] and the testing results indicated that the presence of chromium-rich carbide led to a reduction in the effective hydrogen diffusivity and hindered the crack initiating or propagating.…”

“…[20] and [21], and the chromium concentration in the depleted zone also can be observed by substituting C i Cr ðtÞ into Eq. [19].…”

“…To better understand the fundamental features of the corrosion problems encountered in a high-temperature, aqueous environment associated with steam generators, many kinds of experiments were carried out, [6,16,[19][20][21] such as intergranular attack (IGA) in a certain solution, SCC in sodium thiosulfact (Na 2 S 2 O 3 ) with a small strain rate, etc.…”

The effect of grain boundary misorientation on the intergranular M23C6 carbide precipitation in thermally treated Alloy 690

“…Alloy 690, however, has been found to be immune to IGSCC in various environments [2,3]. Although no clear explanation exists for the improved IGSCC resistance in caustic and de-aerated neutral solutions, it is generally accepted that the precipitation of a high density of intergranular chromium carbides by thermal treatments improves the IGSCC resistance in primary water [4,5] and certain caustic environments [5,6]. Bruemmer et al [7,8] suggested that the intergranular carbides promote crack tip blunting, decrease the crack tip stress state, and therefore, increase the resistance to cracking.…”

Corrosion aspects of Ni–Cr–Fe based and Ni–Cu based steam generator tube materials

“…348 containing much lower amount of nickel with much higher amount of iron and slightly more chromium as compared to Alloy 600 was chosen as SG tubing for Kraft Werk Union (KWU) type PWRs and new Indian PHWRs systems due to its good SCC resistance in pure water and chloride solutions [4][5][6][7]13,15,16]. Investigation on Alloy 600 has been more extensive as compared to Alloy 800 mainly because of more use of Alloy 600 as well as its more corrosion problems in service [16].…”