Corrosion
March 29, 2024

Introduction Carbon Steel Corrosion Charts

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Introduction

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.

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Carbon Steel

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 + H₂SO₄ -> FeSO₄ + H₂

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- -> H₂ (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.

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Corrosion Charts

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) 0-50% H2SO4, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Naturally Aerated, Corrosion Rate = 0.1 mm/y (4 mpy) 0-100% H2SO4, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 0-100% H2SO4, 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 0-100% H2SO4	?
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) 0-50% H2SO4, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Naturally Aerated, Corrosion Rate = 0.1 mm/y (4 mpy) 0-100% H2SO4, 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) 0-50% H2SO4, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Naturally Aerated, Corrosion Rate = 0.1 mm/y (4 mpy) 0-100% H2SO4, 2000 ppm Chloride Ions, Corrosion Rate = 0.1 mm/y (4 mpy) 0-100% H2SO4, 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 625	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief Alloy 625
Alloy C-22	Corrosion Rate	? Haynes International Corrosion Resistant Tech Brief C-22 Alloy
Alloy G-30	Corrosion Rate	? Haynes International Corrosion Resistant Tech Brief G-30 Alloy
Alloy G35	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief G-35 Alloy
Carbon Steel	Isocorrosion Curves	?
Carpenter 20Cb-3	Corrosion Rate in Non-Aerated H2SO4 at 80°C (176°F) Corrosion Rate versus Concentration in Boiling H2SO4, 0-50% H2SO4 Isocorrosion Curves 0-100% H2SO4 Corrosion of Annealed 20Cb-3 to Boiling H2SO4 at Various Concentrations (5%, 10% and 25% H2SO4)	20Cb-3 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 B-2, Cabot Stellite Division, Brochure, 1977
Hastelloy B3	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief B-3 Alloy
Hastelloy C-4	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief C-4 Alloy
Hastelloy C-276	Isocorrosion Curves Sulphuric Acid Sulphuric Acid, 2000 ppm Chlorides	Hastelloy Alloy C-276, Haynes International, Bulletin H-2002B Haynes International Corrosion Resistant Tech Brief C-276 Alloy
Hastelloy D-205	Corrosion Rates Reagent Grade Sulphuric Acid at 93°C - Corrosion Rates 20-60% H2SO4 Commercial Grade Sulphuric Acid at 130°C - Corrosion Rates 96-99% H2SO4	Alfa Laval Brochure ? ?
Hastelloy G	Corrosion Resistance in Non-Aerated Sulphuric Acid at 80°C (176°F)	Carpenter Alloys for Controlling Severe Corrosives, Carpenter Technology Corporation, 9/89-7.5M
Hastelloy Hybrid-BC1	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief Hybrid-BC1 Alloy
HR-235 Alloy	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief HR-235 Alloy
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 H2SO4, 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 S-1875-ENG, July 1992
SAF 2204 UNS S32304	Isocorrosion Curves Deaerated H2SO4, Corrosion Rate = 0.1 mm/y (4 mpy) 0-20% , 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
SAF 3006	Isocorrosion Curve Naturally aerated sulphuric acid 0.1 mm/year (4 mpy) in stagnant test solution	Alleima SAF3006 Tube an Pipe, Seamless, Datasheet
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 80-100% , Static Conditions, Corrosion Rate = 0.1 mm/y (4 mpy) Corrosion Rate = 0.1 mm/y (4 mpy)	Monsanto Enviro-Chem System Brochure Edmeston Materials System Engineering Stainless Steel World (November 2009)
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 S-1875-ENG, July 1992
SARAMET	Isocorrosion Curves	Stainless Steel World (November 2009)
Titanium	Isocorrosion Curves Deaerated H2SO4, Corrosion Rate = 0.1 mm/y (4 mpy) H2SO4 with Copper Sulphate, Corrosion Rate = 0.1 mm/y (4 mpy)	Avesta Sheffield Corrosion Handbook, Avesta Sheffield, 1994
Ultimet Alloy	Isocorrosion Curve Chart	Haynes International Corrosion Resistant Tech Brief ULTIMET Alloy
ZeCor	Isocorrosion Curve 1 mpy, 90-100% H2SO4	? Stainless Steel World (November 2009)
Zeron 100	Isocorrosion Curves Figure 1: Corrosion Rate = 0.1 mm/y (4 mpy) Figure 2: 0-40% H2SO4, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 3: 0-60% H2SO4, 2000 mg/L Cl, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 4: 30-70% H2SO4, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 5: 70-100% H2SO4, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 6: 80-100% H2SO4, Ferrous Ions, Corrosion Rate = 0.1 mm/y (4 mpy) Figure 7: Oleum, 30% SO3, 70-130°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

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