A New Ni-Mo-Cr Alloy for the Most Aggressive Media

摘要

The Ni-Cr-Mo (C-type alloys) are vital to chemical processing industries. This family of alloys is particularly known for its corrosion resistance in hydrochloric and sulfuric acids, at moderate concentrations and temperatures, where some standard stainless steels might not perform well, especially when chlorides are present. Also, the Ni-Cr-Mo alloys possess an excellent resistance to chloride salt solutions which can induce pitting, crevice and stress corrosion cracking. Despite the versatility of Ni-Cr-Mo alloys, there has always been a need for materials with even higher corrosion resistance to hydrochloric and sulfuric acids. Nevertheless, with increasing HCI and H-2SO-4 concentration and temperature, these alloys are prone to some corrosion problems. The Ni-Mo (B-type) and Zirconium alloys are often considered in these cases; however, both systems have significant drawbacks with these two mineral acids and small quantities of oxidizing species can lead to very severe corrosion on these alloys. Therefore, an alloy with improved resistance to hydrochloric and sulfuric acids, relative to the Ni-Cr-Mo alloys and without the drawbacks associated with the Ni-Mo and zirconium alloys was developed. The new material, named HASTELLOY~R HYBRID-BC1~R alloy, falls within the Ni-Mo-Cr system and it fills the gap between the C-type and B-type alloys. This paper will provide detailed comparative corrosion data between the HYBRID-BC1~R alloy and several other Ni-Cr-Mo and Ni-Mo materials in a variety of chemicals, mainly in hydrochloric and sulfuric acids. It was found that the corrosion behavior of the new alloy in these two acids approaches the performance of the B-type alloys, and far exceeds that of the C-type alloys. In addition, the HYBRID-BC1~R alloy exhibited much better tolerance to dissolved oxygen in hot dilute HCI and H2SO4, and also to ferric ions contained in hydrochloric and sulfuric acids.