APPLICATIONS OF ALLOY 59 (UNS N06059) AND ALLOY 31 (UNS N08031) IN MITIGATING CORROSION PROBLEMS IN CPI AND PETROCHEMICAL INDUSTRIES

摘要

CPI & Petrochemicals constitute a huge, complex and highly diverse industry which forms an integral part of the US economy. It covers converting various raw materials (about 10 of them), the most important ones being organic in nature such as oil, natural gas and coal whilst others are inorganic in nature such as ores / elements taken from the earth (phosphates, sulfur, potash etc), air ( nitrogen, oxygen) and water (chlorine, hydrogen). Conversion of these base materials produce about 300 different "intermediates" which then go into production of about 30.000 plus consumer products. The first stage in petrochemical industry is conversion of raw materials into base chemicals (such as syn-gas, ammonia, methanol etc.), lower alkenes such as ethane, propane, butadiene and aromatics such as benzene, toluene, xylenes. The second stage of petrochemical industry consists of various chemical operations with the aim of introducing various hetero-atoms (oxygen, chlorine, fluorine, sulfur etc) into the molecules of base chemicals. This leads to the formation of chemical "intermediates", such as acetic acid, formaldehyde, acetaldehyde and monomers like acrylonitrile, terephthalic acid etc. The third and final step consists of a number of steps to produce consumer goods such as plastics, synthetic fibers, elastomers, insecticides, fertilizers, vitamins, pharmaceuticals, detergents etc. Greater details on these are presented in open literature. Corrosion is an ever-present entity in all these three stages operating 24 hours a day, seven days a week and 365 days a year. Hence suitable materials of construction (MOC) have to be selected to mitigate I minimize I control corrosion. Principal materials of construction typically are carbon & low alloy Cr-Mo steels, standard stainless steels, duplex stainless steels, copper & aluminum alloys, nickel alloys &titanium. In specific cases zirconium and tantalum have also been used. Other corrosion mligation technologies such as electrochemical protection, non-metallics, coatings and paints and use of inhibitor technology also play a major role in combating corrosion. This paper concentrates on presenting the metallurgy, corrosion resistance characteristics of two alloys and their many diverse applications in the industry. One of the alloy belongs to the high performance Ni-Cr-Mo alloy family, alloy 59 ( UNS N06059) whereas the other belongs to the advanced high Cr 6 percent Mo alloy family, alloy 31 ( UNS N08031).