All-purpose weapon in the battle against corrosion

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A new challenge to material quality

The problem is a classic case of “either/or”. In practice, the proportion of oxidizing contaminants is frequently variable and the nature of the acid may change from reducing to oxidizing or vice versa. Plant operators face the same problem when process fluids with opposing properties must be processed in rapid succession.


New processes and product characteristics present a continuous stream of new challenges to material quality in plant engineering. To ensure that the field of plant operation both in and beyond the chemical industry retains its value and cost-effectiveness, a material would be needed that could outperform classic B and C alloys, by coping easily with these changes in fluid properties while also minimizing corrosion.

In fact, a material that is significantly more capable of handling both sets of requirements actually exists; this material combining the best of both worlds is a hybrid alloy.

In technology, “hybrid” – a term derived from the Greek for “mixed, of two origins” – is generally used to denote a system combining two technologies. The prefix “hybrid” indicates a whole that is composed of differing types or processes, with the special feature that each of the combined elements represent individual solutions in themselves – just as the materials listed in the example do for specific groups of process fluids – but, when combined, can create new and desirable properties: here, the capability of processing both reducing and oxidizing materials at high temperatures in one and the same installation.

The new hybrid material: the best of two worlds

The new hybrid material – a nickel-based alloy, for the reasons outlined above – is also manufactured by HAYNES. The HASTELLOY HYBRID-BC1 alloy was developed to fill precisely the gap described, for which no truly effective solution had yet been discovered.

A further example of the ability of a single process fluid to change characteristics can be seen in a series of tests using hydrochloric acid. In Figure 3 the x axis shows the corrosion rate in mm/year for a strongly reducing 2.5% solution of hydrochloric acid (HCl) at 121 °C. The Y axis shows the same HCl with the same parameters, but with one difference: purging with oxygen instead of nitrogen causes the acid to have a strongly oxidizing effect on the metal. In this case, HASTELLOY HYBRID-BC1 alloy (shown in the figure as a red dot) offers an excellent compromise by combining the strengths of alloys from the B and C families, thus significantly reducing the failure risk of both these classic material families in many cases.

Summary: HYBRID-BC1 alloy, featuring “hybrid” properties provided by its composition of 22% molybdenum and 15% chromium, is particularly recommended in cases where both reducing and oxidizing process fluids are used in installations. Today’s chemicals industry is subject to growing pressure; plants are required to perform a variety of chemical operations with varying process media, at ever-shortening process intervals and in batch sizes ranging from small to large.

As a result, the diverse extent of applications offered by the materials used to construct these installations is facing increasingly challenging requirements – which can be effectively fulfilled with the new alloy from HAYNES International. Once again, the Zapp Group is able to supply a material offering highly attractive future potential and filling a major market niche for which no ideal solution has previously been available.

* Reinhart Baden is Technical Customer Service SPECIALTY MATERIALS at Zapp Materials Engineering, Ratingen.