Ammonia induced corrosion of copper effet tubes at Pleystowe Mill

The majority of evaporator tubes now found in the Australian sugar industry are of stainless steel. Previously, the tube material was 70/30 brass but these are susceptible to failure due to stress corrosion cracking. When it came to replace brass tubes in a No. 4 vessel in a quad set in 1982, Pleystowe mill staff selected tubes made of copper, mainly because copper showed a cost saving over stainless steel, and would not be susceptible to stress corrosion cracking. This paper details the tube corrosion problems experienced and the subsequent investigations and equipment modifications made in an attempt to overcome the problem.