ZERON 100 Selected to Replace C-276 Heat Exchanger Tubes

A Spanish hydrometallurgical plant was using C-276 heat exchanger tubing to heat a raffinate solution.  The tubes had steam on the outside at 155°C (inlet) to 100°C (outlet) and raffinate on the inside at 70°C (inlet) to 87°C (outlet).  The raffinate composition was:

Chloride 0.2g/L
Copper 13g/L
Iron 50g/L
Sulphuric Acid 66.5g/L
Zinc 4.9g/L
Arsenic 0.4g/L

The tubes had suffered numerous leaks after 8 months service and the corrosion took the form of pitting of both the seam weld and parent metal (Figures 1 and 2). The reason for the corrosion was that the high concentration of iron and copper made the solution very oxidizing and under these conditions C-276 can go transpassive, when pitting initiates because of the presence of chloride.

Rolled Alloys suggested replacement with ZERON 100 superduplex stainless steel, which has excellent corrosion resistance in raffinates and has a good track record in the copper and nickel hydrometallurgical processing industry.  As ZERON 100 has a much lower nickel content than C-276 it also offered a very cost effective solution to the problem.

C-276
FIGURE 1 Perforation on seam weld of
C-276 heat exchanger tube.

FIGURE 2 Pitting of both parent metal
and seam weld.

ROGER FRANCIS

Corrosion Services Manager