At one time one of the major factors in any material selection used to be initial cost with little thought given to maintenance and cost associated with lost production due to unscheduled equipment downtime. In today's economic environment, increased maintenance costs and downtime have placed a greater emphasis on the need for reliable, safe and
versatile performance of process equipment, thus requiring improved alloys. Today's industries not only demand functional and cost effective reliability in operation, but must also possess the necessary versatility to adopt to the changing corrosive environments, imposed by new processes, changing market needs, and lower quality feedstock. This situation will be made more difficult in the upcoming 21st century due to the need to comply with regulatory requirements of combating pollution. Hence, process machinery, components (vessels, reactors, heat exchangers, etc.) and other parts must be built of suitable materials of construction possessing adequate mechanical, metallurgical and corrosion resistance charaacteristics. This paper presents a chronology of the various corrosion resistant alloys of the "C" family of Ni-Cr-Mo alloys developed in the last 70 years with special emphasis on their applications, particularly alloy 59 (UNS N06059), in CPI and various other industries. Some standard corrosion resistance data comparing the various 'C' family alloys with alloy 59 is also presented along with a section on fabricability/weldability and corrosion resistance of alloy 59 weldments in comparison to the base metal. Keywords: Ni-Cr-Mo alloys, C-family alloys, Alloy 59, UNS N06059, CPI, Applications, Localized corrosion