Corrosion leaking of preheater weldment in alumina factories

Abstract

Stress corrosion cracking (SCC) and anticorrosion measures of TU42C weld-joint were studied by constant load experiments and pickling experiments. The results show that in 40% (mass fraction) NaOH solution at 110 °C, caustic SCC occurs in TU42C weld-joints at the applied potential of −1 020 mV(vs SCE) for 3 d while at the potential of −950 mV(vs SCE) for 10 d. All the cracks are intergranular. In the 10% sulfuric acid, the cracks have the most negative self-corrosion potential −432.5 mV(vs SCE) and are active to be further corroded by the acid. Because of the same corrosion behaviour as the lab weldment, preheater’s cracking in alumina factories is attributed to the combining actions of previous caustic SCC in Bayer solutions and continuous acid corrosion by pickling with the addition of RD. The following measures are effective to prevent the corrosion failure of preheater, such as post-weld heat treatment at 620 °C to relax the residual weld stress, addition of CC3 and L826 as the corrosion inhibitors to improve the pickling and cleaning by the high pressure water instead of by pickling.

Keywords

stress corrosion cracking / constant load experiment / pickling / corrosion inhibitor / postweld heat treatment