CORROSION COMMENTARY

A NEW ALLOY. FEW sections of the chemical industry face bigger corrosion troubles than fertiliser manufacture. In the past a somewhat negative policy has often been followed, letting corrosion have its fling and replacing a plant or new sections of it as and when necessary. This attitude is not as easy to justify today when plant costs are so much higher, and in some factories the development of new processes with greater corrosion risks has greatly accentuated the costs of non‐prevention. The production of high‐analysis phosphatic fertilisers, which involves producing and handling phosphoric acid, is a notable example. With ordinary superphosphate manufacture the main corrosion risk comes from sulphuric acid, but in making so‐called triple superphosphate, which enjoys a high demand from farmers, phosphoric acid is used instead of sulphuric acid to dissolve the mineral rock phosphate. Other modern processes are using nitric acid instead of sulphuric acid, producing an entirely new range of ‘nitro‐phosphates.’