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DKL Engineering, Inc.
Handbook of Sulphuric Acid Manufacturing
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Corrosion
June 6, 2005
Introduction Carbon Steel Corrosion Charts 
Associated Links 
The moment process gases or liquids are introduced to the plant, corrosion begins and the plant starts its slow but sometimes fast decline. Selecting the correct materials of construction is the best method of slowing the progress of corrosion. In order to select the correct material the designer and operator of an acid plant must know how a particular material will withstand exposure to the process conditions.
Although the overall corrosion rate of carbon steel
in concentrated sulfuric acid service is low, some corrosion still occurs.
The reaction products from the corrosion process are iron sulfate and hydrogen
gas.
Fe + H_{2}SO_{4} > FeSO_{4} + H_{2}
This reaction can be considered as the sum of two different reactions occurring at different sites on the metal surface:
Fe > Fe++ + 2e (oxidation)
2H+ + 2e > H_{2} (reduction)
The iron sulphate film is relatively weak and can
be disturbed by high acid velocities or other disturbances in the liquid.
Hydrogen gas can be a problem with carbon steel in
sulphuric acid environments because it can literally scrub off the mechanically
weak iron sulphate film, which is the only thing protecting the steel from
attack.
During periods of normal flow, the gas bubbles are
very small and evenly distributed, and they are quickly carried downstream along
with the acid, generally without causing a problem to the pipe wall.
However, when acid flow stops, the gas bubbles accumulated along the pipe wall
in the upper half of the pipe. When the flow resumed, the hydrogen gas bubbles
are dislodged and rise to the very top of the pipe, scrubbing off the protective
film along the way. With the film gone along the top of the pipe, the surface
corroded very quickly until the iron sulphate film reforms.
Repeating this process over and over again results
in a pattern of curved grooves in the top half of the pipe, all radiating toward
a central longitudinal groove at the very top.
Although we're usually not privileged to see such an excellent example of hydrogen grooving, it's not an uncommon occurrence in sulfuric acid service, particularly under upset conditions. To guard against it, the usual recommendation is to use very thick steel, in recognition of the possibility of localized corrosion, and to keep the average velocity in pipes below 3 ft/sec to reduce the scrubbing effect of any hydrogen bubbles that do form.
Corrosion charts are one source of information that will help identify the correct material of construction for a particular application.
Material  Description  Source 
254 SMo  Isocorrosion Curves Corrosion Rate = 0.1 mm/y (4 mpy) 050% H_{2}SO_{4}, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Naturally Aerated, Corrosion Rate = 0.1 mm/y (4 mpy) 0100% H_{2}SO_{4}, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 0100% H_{2}SO_{4}, 200 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 
654 SMo UNS S32654,
Avesta Bulletin 9603 Avesta Sheffield Corrosion Handbook, Avesta Sheffield, 1994 
300 Series Stainless Steels  Isocorrosion Curves 0100% H_{2}SO_{4} 
? 
310M Stainless Steel  _{Type 310M Corrosion Rates in Strong Sulphuric Acid}  ? 
654 SMo UNS S32654 
Isocorrosion Curves Corrosion Rate = 0.1 mm/y (4 mpy) 050% H_{2}SO_{4}, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Naturally Aerated, Corrosion Rate = 0.1 mm/y (4 mpy) 0100% H_{2}SO_{4}, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 
654 SMo UNS S32654,
Avesta Bulletin 9603 Avesta Sheffield Corrosion Handbook, Avesta Sheffield, 1994 
904L  Isocorrosion Curves Corrosion Rate = 0.1 mm/y (4 mpy) 050% H_{2}SO_{4}, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Naturally Aerated, Corrosion Rate = 0.1 mm/y (4 mpy) 0100% H_{2}SO_{4}, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 0100% H_{2}SO_{4}, 200 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 
654 SMo UNS S32654,
Avesta Bulletin 9603 Avesta Sheffield Corrosion Handbook, Avesta Sheffield, 1994 
Alloy C22  Corrosion Rate  ? 
Alloy G30  Corrosion Rate  ? 
Carbon Steel  Isocorrosion Curves  ? 
Carpenter 20Cb3  Corrosion Rate in NonAerated H_{2}SO_{4}
at 80°C (176°F) Corrosion Rate versus Concentration in Boiling H_{2}SO_{4}, 050% H_{2}SO_{4} Isocorrosion Curves 0100% H_{2}SO_{4} Corrosion of Annealed 20Cb3 to Boiling H_{2}SO_{4} at Various Concentrations (5%, 10% and 25% H_{2}SO_{4}) 
20Cb3 Stainless Steel, Carpenter Technology Brochure 
Chlorimet 2  Isocorrosion Curves  The Duriron Company, Inc., Bulletin A/3g, April 1987 
Chlorimet 3  Isocorrosion Curves  The Duriron Company, Inc., Bulletin A/3g, April 1987 
Durimet 100  Isocorrosion Curves Corrosion Rate = 20 mpy 

Durimet 20  Isocorrosion Curves Corrosion in Sulphuric Acid Corrosion Rate = 20 mpy 
Durimet 20, Bulletin
A/1h, The Duriron Company, Inc., January 1985 Durimet 100, Bulletin A/7g, The Duriron Company, Inc., July 1987 
Duriron  Isocorrosion Curves  Duriron, Duchlor 51, Superchlor, Bulletin A/2g, The Duriron Company, Inc., March 1986 
Hastelloy B2  Isocorrosion Curves Sulphuric Acid Sulphuric Acid, 200 ppm Chlorides 
Hastelloy Alloy B2, Cabot Stellite Division, Brochure, 1977 
Hastelloy C276  Isocorrosion Curves Sulphuric Acid Sulphuric Acid, 2000 ppm Chlorides 
Hastelloy Alloy C276, Haynes International, Bulletin H2002B 
Hastelloy D205  Corrosion Rates Reagent Grade Sulphuric Acid at 93°C  Corrosion Rates 2060% H_{2}SO_{4} Commercial Grade Sulphuric Acid at 130°C  Corrosion Rates 9699% H_{2}SO_{4} 
Alfa Laval Brochure ? ? 
Hastelloy G  Corrosion Resistance in NonAerated Sulphuric Acid at 80°C (176°F)  Carpenter Alloys for Controlling Severe Corrosives, Carpenter Technology Corporation, 9/897.5M 
Inconel Alloy 686  General Corrosion Resistance Isocorrosion Curve, 20 mpy (0.51 mm/y) Isocorrosion Curves 
Magazine advertisement Special Metals Technical Brochure 
Lead  Isocorrosion Curve Corrosion Rate = 5 mpy 

Niobium  Isocorrosion Curve Corrosion Rate = 5 mpy 

Noridur 9.4460  Isocorrosion Curves Aerated, Velocity = 10 m/s, Corrosion Rate = 0.5 mm/y 
KSB, Klein, Schanzlin & Becker Aktiengesellschaft, I/1980 
SAF 2205 UNS S31803 
Isocorrosion Curves Deaerated H_{2}SO_{4}, Corrosion Rate = 0.1 mm/y (4 mpy) Corrosion Rate = 0.1 mm/y (4 mpy) Static Conditions, Corrosion Rate = 0.1 mm/y (4 mpy) 
Avesta Sheffield Corrosion
Handbook, Avesta Sheffield, 1994 Avesta 2205, UNS 31803, Avesta Bulletin 9060 Sandvik Steel, Bulletin S1875ENG, July 1992 
SAF 2204 UNS S32304 
Isocorrosion Curves Deaerated H_{2}SO_{4}, Corrosion Rate = 0.1 mm/y (4 mpy) 020% , Static Conditions, Corrosion Rate = 0.1 mm/y (4 mpy) 
Avesta Sheffield Corrosion
Handbook, Avesta Sheffield, 1994 Avesta SAF 2304, UNS S32304, Avesta Bulletin 9137 
Sandvik HT 9067  Isocorrosion Curves Corrosion Rate = 0.1 mm/y (4 mpy) 
Edmeston HT Alloy Brochure 
Sandvik SX  Corrosion Rates  Static
Conditions Isocorrosion Curves 80100% , Static Conditions, Corrosion Rate = 0.1 mm/y (4 mpy) Corrosion Rate = 0.1 mm/y (4 mpy) 
Monsanto EnviroChem System
Brochure Edmeston Materials System Engineering 
Sanicro 28  Isocorrosion Curves Naturally aerated, Corrosion Rate = 0.1 mm/y (4 mpy) Stagnant, Corrosion Rate = 0.1 mm/y (4 mpy) 
Avesta Sheffield Corrosion
Handbook, Avesta Sheffield, 1994 Sandvik Steel, Bulletin S1875ENG, July 1992 
Titanium  Isocorrosion Curves Deaerated H_{2}SO_{4}, Corrosion Rate = 0.1 mm/y (4 mpy) H_{2}SO_{4} with Copper Sulphate, Corrosion Rate = 0.1 mm/y (4 mpy) 
Avesta Sheffield Corrosion Handbook, Avesta Sheffield, 1994 
ZeCor  Isocorrosion Curve 1 mpy, 90100% H_{2}SO_{4} 
? 
Zeron 100  Isocorrosion Curves Figure 1: Corrosion Rate = 0.1 mm/y (4 mpy) Figure 2: 040% H_{2}SO_{4}, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 3: 060% H_{2}SO_{4}, 2000 mg/L Cl, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 4: 3070% H_{2}SO_{4}, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 5: 70100% H_{2}SO_{4}, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 6: 80100% H_{2}SO_{4}, Ferrous Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 7: Oleum, 30% SO_{3}, 70130°C 
The Performance of Zeron 100 Super Duplex Stainless Steels in Sulphuric Acid, Weir Materials & Foundries 
Zirconium  Isocorrosion Curve, Corrosion Rate = 5 mpy  Wah Chang Magazine Advertisement 