Processing oil and natural gas typically involves dealing with impurities, breaking down compounds into their basic elements, and operating over a wide range of temperatures, some of them very high. Below are some of the most common corrosive compounds encountered in a variety of processes in the oil and gas industry.
Sulphur: Present in raw crude, sulphur combines with other elements to form sulphides, sulphuric acids, polythionic acids, and other aggressive compounds. Sulphur can also cause sulphidation of metals at high temperatures.
Phenols: Often encountered in processes involving sour water strippers.
Naphthenic Acid: A group of organic acids typically found in Western and Mid-East US crude oils.
Chlorides: Often found in catalysts, cooling waters, and crude oil, salts can increase corrosion resistance. Examples of chlorides include magnesium chloride and calcium chloride.
Polythionic Acid: Typically created while equipment is not in operation, these acids are the result of sulphides, moisture, and oxygen interacting.
Cyanides: Responsible for increasing corrosion rates, cyanides often form during the cracking process of feedstocks high in nitrogen.
Hydrogen Chloride: The result of hydrolysis of magnesium chloride and calcium chloride, hydrogen chloride is found in many vapour streams. Once condensed, it converts to hydrochloric acid -- a highly aggressive corrosion agent.
Ammonia: Often the start of forming other corrosive substances -- such as ammonium chloride -- ammonia is a common result of hydrogen interacting with the nitrogen in feedstocks.
Sulphuric Acid: Formed when sulphur trioxide, water, and oxygen combine, this aggressive compound also serves as a process catalyst in alkylation plants.
Hydrogen: While not directly corrosive, hydrogen is a factor in steel embrittlement and interacts readily with other compounds to create corrosive agents.
Oxygen: Like hydrogen, oxygen is not a direct threat. In fact, oxygen is a critical component in refreshing stainless steel’s passivation layer. However, it’s also used in a number of processes that can cause oxidation or scaling.
Carbon Dioxide: A byproduct of hydrogen plants and catalytic cracking processes, carbon dioxide can create carbonic acid when combined with moisture.
Carbon: Also not directly corrosive. However, can lead to carburization at higher temperatures, causing steel embrittlement and reducing corrosion resistance allowing other corrosive compounds to initiate attacks.This puts stainless steel in a position unmatched by other metals. Although carbon steel is suitable for some low temperature, high pressure, or corrosion conditions, the variety of stainless steel alloys ensures protection during the purification of the most corrosive oil and gas.