|
Knowledge for
the Sulphuric Acid Industry
Introduction
General
Definitions
Instrumentation
Plant Safety
Metallurgial
Processes
Metallurgical
Sulphur Burning
Acid Regeneration
Lead Chamber
Technology
Gas Cleaning
Contact
Strong Acid
Acid Storage
Loading/Unloading
Transportation
Sulphur Systems
Liquid SO2
Boiler Feed Water
Steam Systems
Cooling Water
Effluent Treatment
Utilities
Construction
Maintenance
Inspection
Analytical Procedures
Materials of Construction
Corrosion
Properties
Vendor Data
Google Search
| |
Corrosion
June 6, 2005
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.
Back to top
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.
Back to top
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 C-22 |
Corrosion Rate |
? |
| Alloy G-30 |
Corrosion Rate |
? |
| 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 C-276 |
Isocorrosion Curves
Sulphuric Acid
Sulphuric Acid, 2000 ppm Chlorides |
Hastelloy Alloy C-276, Haynes
International, Bulletin H-2002B |
| 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 |
| 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 |
| 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 |
| 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 |
| 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 |
| ZeCor |
Isocorrosion Curve
1 mpy, 90-100% H2SO4 |
? |
| 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 |
Back to top
|
