Refining oil and gas is an extensive process with many byproducts and cyclical processes designed to optimize efficiency and make use of as many of the compounds and chemicals involved as possible.
Unfortunately, many of those processes create or involve the use of highly-corrosive compounds. As such, stainless steel is a critical component in the design and safe operation of many oil and gas processing systems.
In this guide, we’ll look at established uses for stainless steel and prevailing considerations for choosing the ideal stainless steel materials for a range of oil and gas industry processes.
Corrosives Encountered in Refining Processes
Processing oil and gas often involves dealing with impurities, breaking down compounds into their base elements, and operating at a wide range of temperatures — some of them very high.
The following are some of the most common corrosive compounds encountered in the various processes employed across 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.
- Naphthenic Acid: A group of organic acids typically found in Western and Mid-East US crude oils.
- Polythionic Acid: Typically created while equipment is not in operation, these acids are the result of sulphides, moisture, and oxygen interacting.
- Chlorides: Often found in catalysts, cooling waters, and crude oil, salts can increase corrosion resistance. Examples of chlorides include magnesium chloride and calcium chloride.
- Carbon Dioxide: A byproduct of hydrogen plants and catalytic cracking processes, carbon dioxide can create carbonic acid when combined with moisture.
- 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.
- 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.
- 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.
- Phenols: Often encountered in processes involving sour water strippers.
- 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: 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 that few other metals can match. While carbon steel is suitable for some low-temperature, -pressure, or -corrosion situations, the variety of stainless steel alloys available ensures there is an option to provide protection against even the most corrosive oil and gas refinement processes.
Oil and Gas Processing Applications for Stainless Steel
With an understanding of traditional corrosion factors and risks, we can look at how stainless steel offers ways to mitigate risks and provide long-lasting protection and performance. The following applications are some of the most popular uses for stainless steel in the oil and gas industry.
Corrosion concerns related to crude distillation include elevated temperature sulphidation and attack by naphthenic acid corrosion.
Typically uses types 304, 316, 405, and 410. 304 is excellent between 260-399C (500-750F) while 400-series stainless steels offer resistance at higher ranges, up to 343-371C (650-700F.) 304 also provides excellent naphthenic acid corrosion resistance.
For situations requiring increased resistance, type 329, 6X, 29-4, and 26-1 steels are possible alternatives.
Areas where stainless steel is often used in the crude distillation process include:
- Preheat trains and transfer lines leaving the preheat furnaces
- Atmospheric fractionators
- Column inlet nozzles and flash sections
- Draw lines or side cuts
- Heat exchanger tubes
- Vacuum flasher towers, furnaces, and bottom lines
- Stabilizer reboilers
- Overhead condensers
Fluid Catalytic Cracking
Corrosion concerns related to fluid catalytic cracking include high-temperature carburization of steel, oxidation, and sulphidation.
Typical types of steel used include types 304, 321, 347, 405, and 410. Austenitic grades are often ideal choices.
For processes involving high cyanide levels, types 316, 317, 6X, and 29-4 can provide increased resistance.
Areas where stainless steel is often used in the fluid catalytic cracking process include:
- Air distribution and injection systems
- Regenerator plenums
- Overflow valves
- Feed nozzles and transfer lines
- Reactor liners
- Shed and fractionating trays
- Overhead condensers
- Fittings, pumps, and valves
Corrosion concerns related to delayed coking often revolve around embrittlement. However, ammonia, cyanide, and hydrogen sulphide are often fractions of the coking process.
For high-temperature uses (those exceeding 371C or 700F,) type 304 or 316 are good starting points. For lower-temperature processes, types 410 and 405 are common.
High cyanide processes can see additional resistance using 6X or 29-4 alloys.
Areas where stainless steel is often used in the delayed coking process include:
- Coke drum pumps, heaters, and transfer piping
- Furnaces and transfer lines
- Recycle heat exchangers
- Steam and gas oil strippers
- Overhead condensers
Corrosion concerns related to hydrotreating often revolve around exposure to ammonia, ammonium hydrosulphide, hydrogen sulphide, and polythionic acids as well as embrittlement due to high temperatures and pressures.
Types used often include 304, 308, 321, 347, 405, 410, and 430.
Areas where stainless steel are often used in the hydrotreating process include:
- Feed-effluent heat exchangers
- Hot piping and heater tubes
- Reactor piping
- High- and low-pressure reactors
- Bed supports, distributor trays, thermowells, and scale baskets
- Tube sheets and vessel nozzles
- U-bend style heat exchangers
- Fractionators and fractionator feed exchangers
- Air, gas, and naphtha coolers
Corrosion concerns related to catalytic reforming often include the formation of ammonium chloride and pitting corrosion from cooling water.
Types used often include 304, 316, 329, 6X, and 29-4.
Areas where stainless steel is often used in the catalytic reforming process include:
- Reactor internals, such as shrouds, thermowells, catalyst support devices, and screens
- Reformate coolers
- Trays, downcomers, and beams in the stabilizer
Corrosion concerns related to hydrocracking often involve embrittlement and polythionic stress-corrosion cracking. However, the presence of hydrogen in many processes can also pose corrosion risks depending on the compounds created or processed.
Types used often include 304, 321, 347, 410, 430, 18-2, and 26-1 as well as precipitation hardening and austenitic steels.
Areas where stainless steel is often used in the hydrocracking process include:
- Heat exchangers
- Feed effluent exchangers
- Feed piping
- Feed heaters
- Reactor shell clads or overlays
- Reactor nozzles, bed supports, catalyst screens, thermowells (and sheathes), and gasketing
- Stabilizer feed heaters
- Air cooler components
- Stabilizer and fractionator internal components
Corrosion concerns related to hydrogen plants often involve high temperatures and pressures as well as frequent exposure to carbonic acid.
Types used often include 304, 304L, 310, 330, 410, 430, and cast grade ACI HK-40.
Areas where stainless steel is often used in the hydrogen plants include:
- Steam superheater components
- Vertical reformers
- Catalyst-filled tubing
- Tubing pigtails and sub-headers
- Shift gas piping
- Solvent boilers
- Knockout pots
- Intermediate air coolers
- Tower shells
Corrosion concerns related to gas plants often relate to ammonia, chlorides, hydrogen cyanide, hydrogen sulphide, and water with hydrogen blistering and sulphide cracking being predominant risks.
Types used often include 304, 304L, 316, 316L, 329, 405, 410, 26-1, 29-4, 29-4-2, 6X, and Nitronic 50. Austenitic grades often work well for linings thanks to their increased hydrogen sulphide resistance.
Areas where stainless steel is often used in gas plants include:
- Compressor inter- and after-cooler tubing and shells
- Depentanizer columns, preheaters, and reboilers
- Depropanizer trays
- Bebutanizer trays
- Reboiler tubing
Corrosion concerns related to amine plants often relate to hydrogen sulphides and carbonic acid.
Types used often include 304, 316, 329, 410, 430, and 20Cb-3.
Areas where stainless steel is often used in amine plants include:
- Rich/lean exchangers
- Regenerator boilers
- Pre-coat filter elements
- Reclaimer tubing
- Overhead gas coolers
Sulphuric Acid Alkylation
Corrosion concerns related to sulphuric acid alkylation often related to the sulphuric acid used in the process.
Types used often include 316, 316L, and 20Cb-3
Areas where stainless steel is often used in the sulphuric acid alkylation process include:
- Feed piping
- Caustic wash systems
- Water-wash vessels
- Overhead accumulators
- Rerun columns
- Reboiler tubing
- Condenser tubing and linings
- Fractionation tray parts
- Valve and pump trim and seals
Sour Water Strippers
Corrosion concerns related to sour water strippers vary based on the waste-water treated. However, common corrosion factors include hydrogen sulphide and cyanides.
Types used often include 304, 316, 410, 20Cb-3, 29-4, 29-4-2, 6X, and Nitronic 50.
Areas where stainless steel is often used in sour water strippers include:
- Towers and acid mixing columns
- Tower trays
- Overhead exchangers and air coolers
- Reflux drums, lines, pumps, and control valves
- Effluent coolers
- Reboiler shells and tubing
- Stainless steel offers a wide range of alloys and characteristics to provide benefits to the vast range of processes used in modern oil and gas industry.
- Matching alloys to the specific corrosive compounds and conditions of a process will ensure long-lasting performance and safe operation.
- Common corrosion agents include sulphur, naphthenic acid, polythionic acid, chlorides, carbon dioxide, ammonia, cyanides, hydrogen chloride, sulphuric acid, hydrogen, phenols, oxygen, carbon.
- Popular grades and types of steel used in the gas and oil industry include 304, 304L, 308, 310, 316, 317, 321, 329, 330, 347, 405, 410, 430, 18-2, 20Cb-3, 29-4, 29-4-2, 26-1, 6X, Nitronic 50, ACI HK-40.
Unified Alloys is a leading provider of stainless steel materials and components to major gas and oil industry throughout Canada and the rest of North America. Our extensive selection and decades of experience mean we can help you find the ideal product or solution, whether you’re designing new facilities or maintaining or retrofitting existing equipment. Call today to speak with one of our expert sales analysts.
- Nickel Institute: The Role of Stainless Steels in Petroleum Refining
- Parker: Beyond Stainless Steel: Corrosion Resistant Alloys in the Oil and Gas Industry
- Northern Weldarc Ltd: Uses of Steel in Oil and Gas Industry
- TWI Global: Welding New Stainless Steels For The Oil And Gas Industry
- Stainless Steel World: Overview Of Typical Applications For Stainless Steels
- One Petro: Application Limits of Stainless Steels in the Petroleum Industry
- Northwestern University: Materials Of Crude Oil Materials Of Crude Oil Refining: Corrosion Problems And Prevention
- ASM International: Corrosion in Petroleum Refining and Petrochemical Operations
- Chron: The Types of Metals Used in the Oil & Gas Industry
- Materials Performance: Stress Cracking of Duplex Stainless Steel in Refining