Effect of flowing sodium on corrosion and tensile properties of AISI type 316LN stainless steel at 823K

Carburization behavior of AISI 316LN austenitic stainless steel – Experimental studies and modeling

“…Analysis of the high resolution spectrum for nickel revealed its presence only in the elemental form at a BE of 853 eV which is close to the value reported [17] for Ni 2p peak at 852.7 eV. XPS analysis confirmed the absence of ternary oxides of Na and Cr which are expected to form for lower oxygen concentrations [2]. The oxygen content in sodium was probably below the threshold level required for the formation of ternary compounds or they would have got removed during the cleaning process.…”

“…where [O] is the concentration of oxygen in sodium in wppm, R is the gas constant in JK À1 mol À1 and T is the temperature in K. From the above expression loss of material due to leaching at a temperature of 798 K was found to be 4.6 lm for 16,000 h. Similarly the thickness of the ferrite layer ('Y') in 316LN stainless steel at 798 K for 16,000 h was calculated as 11.4 lm using the following expression given in literature [13].…”

“…Even though width of the carburized zone has been predicted using the model, two other phenomena namely leaching and formation of degraded layer which affect the wall thickness of the exposed material has not been considered. For oxygen content in sodium in the range of 2-9 wppm the recommended expression for loss of the material due to leaching is [13] Sðlm=yearÞ ¼ 25 exp ð5:62 þ 3:45log 10 ½O À 75312=RTÞ ð 8Þ…”

“…When oxygen concentration is less than 10 wppm, chromium present in steel can combine with oxygen and sodium to form a ternary compound namely NaCrO 2 [2]. For higher oxygen concentrations formation of ternary compounds of other transition metals has been observed [3].…”

“…The authors have investigated in detail [13,14] the behavior of primary circuit materials in liquid sodium containing 25 wppm of carbon by employing a monometallic sodium loop called as the Mass Transfer Loop (MTL). To get further insight into the long term carburization/decarburization behavior of steels in the simulated environment of the secondary circuit of PFBR (comprising the IHX and steam generator) a bi-metallic (BIM) sodium loop was constructed.…”