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Influence of heat flux and surface temperature on the intergranular corrosion of stainless steel

The exposure tests followed by metallographic evaluation and the electrochemical reactivation measurements in double‐loop (DL‐EPR) modification were used for investigation of the influence of non‐boiling heat transfer on initiation and rate of propagation of intergranular corrosion (IGC) of sensitized austenitic stainless steel EN 1.4301 (AISI 304) in sulfuric acid solutions. The influence of heat flux and surface temperature was ascertained separately. The susceptibility to IGC and the rate of crack propagation increased with the surface temperature. Heat flux from metal to solution at constant surface temperature facilitated the IGC initiation, but at the same time it caused a drop of the corrosion attack depth in the metal. The increase of the heat flux by 10 kW m−2 in a range from 0 to 42 kW m−2 led to a drop of the maximum depth of cracks formed after subsequent bending the specimen, in average by 8%. The overall danger of corrosion was lower at positive heat flux between metal and solution than under isothermal conditions at constant surface temperature of the metal. The intensification of heat flux by 10 kW m−2 had the same effect on the IGC as a change of the surface temperature by less than 2 K. Therefore, the effect of the heat flux on IGC of the heat exchangers operating under non‐boiling conditions may be considered as relatively less important than the effect of the surface temperature.