Corrosivity of final evaporator condensates at four Australian sugar factories

Recent studies of steam-efficient evaporator stations in Australian factories show that sucrose degradation and the subsequent formation of acids in the juice produces final evaporator condensates of low pH (sometimes less than 5). Using corrosion coupons, the corrosivity of final condensates was investigated at four factories for four materials commonly used in the construction of evaporators and the ancillary pipework. On-line measurements of pH and instantaneous corrosion rates were also made. The two steam-efficient factories had very high corrosion rates for the carbon-steel coupons (pipework and tube-plate materials), while the factory with no vapour bleed (low steam-efficiency configuration) had much lower corrosion rates for these materials. One factory with a relatively low pH of condensate, but with low pH not as a consequence of sucrose degradation, showed intermediate corrosion rates. For all four factories, 304 stainless-steel coupons showed extremely low corrosion rates. The results demonstrate the need for steam efficient factories to determine appropriate solutions to extend the service lives of the evaporator vessels. Such solutions may include operational changes, design changes to evaporators and/or the use of alternative materials such as 304 stainless steel for vessel construction.