CICIND Metallic Materials Manual - E
CICIND METALLIC MATERIALS MANUAL March 2003
CICIND documents are presented to the best of the knowledge of its members as guides only. CICIND is not, nor are any of its members, to be held responsible for any failure alleged or proved to be due to adherence to recommendations, or acceptance of information, published by the association in a Model Code or other publication or in any other way.
Copyright CICIND 2002 ISBN 1-902998-16-2 Office of the Secretary, 14 The Chestnuts, Beechwood Park, Hemel Hempstead, Herts. HP3 0DZ, UK Tel: +44 (0)1442 211204 Fax: +44 (0)1442 256155 e-mail:
[email protected]
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CICIND Metallic Materials Manual - E
CICIND Metallic Materials Manual - E
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CICIND METALLIC MATERIALS MANUAL
NOTE
THE DATA IN TABLES, DIAGRAMS AND DATA SHEETS ARE INTENDED AS GENERAL INFORMATION ONLY. FOR DESIGN PURPOSES IT IS IMPERATIVE THAT REFERENCE BE MADE TO APPROPRIATE MATERIALS STANDARDS AND SPECIFICATIONS; ALSO TO MATERIALS PRODUCERS AND APPROPRIATE NATIONAL DIRECTIVES
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CICIND Metallic Materials Manual - E
CICIND Metallic Materials Manual - E
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TABLE OF CONTENTS 1.
BACKGROUND .......................................................................................................................1–1 1.1 1.2 1.3 1.4 1.5
2.
General ................................................................................................................................................................1–1 Acknowledgements .............................................................................................................................................1–1 Layout of Manual ...............................................................................................................................................1–1 Units conversion..................................................................................................................................................1–1 Commonly Used Chemical Elements ................................................................................................................1–2
INTRODUCTION.....................................................................................................................2–1 2.1 Acid Dewpoint Corrosion...................................................................................................................................2–1 2.1.1 Dewpoint.......................................................................................................................................................2–1 2.2 Metallic Chimneys and Flues.............................................................................................................................2–2 2.2.1 Material Groups ...........................................................................................................................................2–3 2.2.2 Metallic Materials for Chimneys and Flues...............................................................................................2–3
3.
GUIDE TO MATERIAL SELECTION .................................................................................3–1 3.1 Criteria ................................................................................................................................................................3–1 3.1.1 Temperature .................................................................................................................................................3–1 3.1.2 Chemical Loadings ......................................................................................................................................3–1 3.1.3 Corrosion Allowance ...................................................................................................................................3–1
4.
METALLIC MATERIALS STRUCTURAL APPLICATIONS.........................................4–1 4.1 Structural Steels..................................................................................................................................................4–1 4.2 Weathering Steels ...............................................................................................................................................4–1 4.3 Stainless Steels, Nickel Base Alloys and Titanium ...........................................................................................4–2 4.3.1 Stainless Steels .............................................................................................................................................4–2 4.3.2 Nickel Alloys and Titanium .........................................................................................................................4–2 4.4 Chemical effects ..................................................................................................................................................4–3 4.5 Allowance for Corrosion ....................................................................................................................................4–3
5.
STAINLESS STEELS ............................................................................................................5–1 5.1 Introduction ........................................................................................................................................................5–1 5.2 Guidelines for Selection......................................................................................................................................5–1 5.3 Basic Grades of Stainless Steels .........................................................................................................................5–1 5.3.1 Austenitic Stainless Steels............................................................................................................................5–1 5.3.2 Ferritic Stainless Steels................................................................................................................................5–1 5.3.3 Duplex Stainless Steels ................................................................................................................................5–2 5.4 Material Selection ...............................................................................................................................................5–2 5.5 Corrosion Resistance ..........................................................................................................................................5–2 5.6 High-Temperature Corrosion Resistance.........................................................................................................5–4 5.7 High Performance Grades .................................................................................................................................5–4 5.7.1 Austenitic High Performance Stainless Steels............................................................................................5–5 5.7.2 Duplex High Performance Stainless Steels.................................................................................................5–5 5.7.3 Mechanical Properties .................................................................................................................................5–6 5.7.3.1. 5.7.3.2.
5.7.4 5.7.5
Physical Properties.......................................................................................................................................5–6 Corrosion Resistance of High Performance Stainless Steels in Flue Gas Environments.........................5–6
5.7.5.1. 5.7.5.2. 5.7.5.3. 5.7.5.4. 5.7.5.5.
5.8 5.9
6.
Austenitic Stainless Steels. .........................................................................................................................................5–6 Duplex Stainless Steels...............................................................................................................................................5–6
Resistance to Inorganic Acids.....................................................................................................................................5–6 Sulphurous Acid. ........................................................................................................................................................5–7 Chloride - and Other Halide Ion-Containing Aqueous Environments. .......................................................................5–7 Ranking of Individual Grades.....................................................................................................................................5–7 Acidic Environments Containing Halides - Flue Gas Condensates. ...........................................................................5–7
Corrosion Acceptance Tests...............................................................................................................................5–8 Potential substitution of super-austenitic stainless steel for nickel base alloys..............................................5–9
NICKEL ALLOYS ..................................................................................................................6–1 6.1 6.2
Effects of Alloying in Stainless Steels and Nickel Alloys .................................................................................6–1 Selection and Performance of Materials...........................................................................................................6–1
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7.
CICIND Metallic Materials Manual - E
TITANIUM ...............................................................................................................................7–1 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10
8.
Titanium Linings ................................................................................................................................................ 7–1 Definition of the Operating Environment ........................................................................................................ 7–1 Resistance of Titanium to hot concentrated reducing acids ........................................................................... 7–1 Resistance of Titanium to fluoride species ....................................................................................................... 7–1 Selection............................................................................................................................................................... 7–1 Design Stresses.................................................................................................................................................... 7–2 Physical Properties ............................................................................................................................................. 7–2 Product Form...................................................................................................................................................... 7–2 Installation .......................................................................................................................................................... 7–2 References ........................................................................................................................................................... 7–2
ELEVATED TEMPERATURE PROPERTIES....................................................................8–1 8.1 Introduction ........................................................................................................................................................ 8–1 8.2 Elevated Temperature Properties..................................................................................................................... 8–1 8.3 High Temperature Design Factors.................................................................................................................... 8–1 8.3.1 Service Life .................................................................................................................................................. 8–1 8.3.2 Allowable Deformation................................................................................................................................ 8–1 8.3.3 Environment ................................................................................................................................................ 8–1 8.3.4 Cost............................................................................................................................................................... 8–2 8.4 Criteria for Selection.......................................................................................................................................... 8–2 8.4.1 Short-Time Tensile Properties .................................................................................................................... 8–2 8.4.2 Creep ............................................................................................................................................................ 8–2 8.4.3 Creep-Rupture ............................................................................................................................................. 8–2 8.4.4 Thermal Stability ......................................................................................................................................... 8–3 8.4.5 Physical Properties ...................................................................................................................................... 8–3 8.4.6 Modulus of Elasticity................................................................................................................................... 8–3 8.5 Effect of Atmosphere.......................................................................................................................................... 8–3
9.
LOW TEMPERATURE PROPERTIES..............................................................................9–1
10. .......................................................................................................................................................10–1 11. .......................................................................................................................................................11–1 12. 12.1
USEFUL INFORMATION....................................................................................................12–1 Material Data Sheets ........................................................................................................................................ 12–1
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LIST OF TABLES Table 1-1 Commonly Used Elements...................................................................................................................................1–2 Table 3-1 Corrosion allowance for the sheet steel thickness for general structural steels and for creep-resistant steels .3–2 Table 3-2 Addition to sheet steel thickness when using rust-resistant steels subject to aggressive condensates .................3–2 Table 3-3 Steel yield strength values (fy,k) at temperature from prEN13084-7:2001 ..........................................................3–3 Table 4-1 Limits of exposure to acidic condensation ..........................................................................................................4–3 Table 4-2 External corrosion allowance (CE).....................................................................................................................4–4 Table 4-3 Internal corrosion allowance (CI).......................................................................................................................4–5 Table 4-4 Minimum strengths inN/mm2 ...............................................................................................................................4–6 Table 4-5 Impact values for nominal thickness 10-150mm ..................................................................................................4–6 Table 4-6 Indication of maximum temperatures commonly used for structural steels ........................................................4–6 Table 4-7 Suggested maximum service temperatures in air for stainless steels ..................................................................4–6 Table 4-8 Summary of data on corrosion resistance of carbon steel and A242 Type 1 HSLA steel in natural gas combustion products............................................................................4–7 Table 5-1 Austenitic Stainless Steels .................................................................................................................................5–10 Table 5-2 Guideline to relative corrosion resistance of basic stainless steels ..................................................................5–10 Table 5-3 Type 316 S31600 Steel Properties.....................................................................................................................5–11 Table 5-4 Type 316 S31600 Steel Properties....................................................................................................................5–12 Table 5-5 Type 317 Stainless Steel (S31700) Properties...................................................................................................5–13 Table 5-6 Type 410 Stainless Steel (S41000) Properties...................................................................................................5–14 Table 5-7 Type 410 Stainless Steel (S41000) Properties ..................................................................................................5–15 Table 5-8 Modulus of elasticity at various temperatures...................................................................................................5–16 Table 5-9 Modulus of rigidity at various temperatures .....................................................................................................5–16 Table 5-10 Poisson’s Ratio at various temperatures..........................................................................................................5–16 Table 5-11 Suggested suitability of linings for steel stacks to withstand chemical and temperature environments of flue gas........................................................................................................5–17 Table 5-12 Chemical Composition1 of wrought high-performance austenitic stainless steels (wt. pct)2............................5–18 Table 5-13 Chemical Composition1 of wrought high-performance duplex stainless steels (wt. pct)2 ................................5–19 Table 5-14 Minimum mechanical properties in basic ASTM specifications for high performance austenitic stainless steels ..................................................................................................................................5–19 Table 5-15 High performance austenitic stainless steels ASME allowable design stress values (ksi) ...............................5–20 Table 5-16 Minimum mechanical properties in basic ASTM specifications for high performance duplex stainless steels .......................................................................................................................................5–20 Table 5-17 High performance duplex stainless steels ASME allowable design stress values (ksi) ....................................5–21 Table 5-18 Ambient temperature physical properties of high performance austenitic stainless steels ..............................5–21 Table 5-19 Ambient temperature physical properties of high perfromance duplex stainless steels ...................................5–22 Table 6-1 Selection of nickel alloys in ascending order of PRENW....................................................................................6–2 Table 6-2 PRENW values for increasing alloy content .......................................................................................................6–2 Table 6-3 Limiting chemical composition for C276 ............................................................................................................6–2 Table 6-4 Physical properties of C276 at high temperatures ..............................................................................................6–3 Table 6-5 Physical properties for C276 ..............................................................................................................................6–3 Table 6-6 Typical room temperature tensile properties of annealed C276 material...........................................................6–4 Table 6-7 Guidelines for the selection of stainless steel and nickel alloy for FGD equipment ...........................................6–4 Table 6-8 Guidelines for material selection for FGD equipment - Temperature 50-65°C* ................................................6–4 Table 7-1 Composition of commonly used titanium alloys ..................................................................................................7–3 Table 7-2 Suitability of titanium alloys for different operating conditions..........................................................................7–3 Table 7-3 Titanium Alloy Design Stresses ...........................................................................................................................7–4 Table 7-4 Titanium Alloy Physical Properties.....................................................................................................................7–4 Table 8-1 Steel yield strength values (fy,k) at temperature from prEN13084-7:2001 ..........................................................8–5 Table 8-2 Short term tensile properties ...............................................................................................................................8–6 Table 8-3 Suggested maximum service temperatures in air .................................................................................................8–6 Table 8-4 Physical properties of Type 309 (S30900) ...........................................................................................................8–6 Table 8-5 Physical properties of Type 309 (S30900) ...........................................................................................................8–7 Table 8-6 Physical properties of Type 310 (S31000) ...........................................................................................................8–8 Table 8-7 Physical properties of Type 310 ...........................................................................................................................8–9 Table 8-8 Elevated temperature physical properties of high-performance austenitic stainless steels ...............................8–10 Table 8-9 Elevated temperature physical properties of high-performance duplex stainless steels ....................................8–11
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LIST OF FIGURES Figure 4-4 Comparison of corrosion rates under exposure to fuel-oil combustion-product gas ........................................4–8 Figure 5-1 Operating zones in a generic FGD system as defined in ASTM STP 837 ..........................................................5–8 Figure 5-2 Commonly used grades of stainless steel.........................................................................................................5–23 Figure 5-3 Corrosion rates for stainless steels in various gases.......................................................................................5–24 Figure 5-4 Solid solution strengthening effects by alloying in austenitic stainless steels ..................................................5–24 Figure 5-5 Effect of nitrogen on the strength and ductility of Type 304 stainless steel.....................................................5–25 Figure 5-6 Strengthening effect of nitrogen in high performance austenitic stainless steels as manifested in ASTM A240 minimum strength requirements.....................................................................5–25 Figure 5-7 High temperature strength of austenitic stainless steels...................................................................................5–26 Figure 5-8 High temperature strength of duplex high performance stainless steels ..........................................................5–26 Figure 5-9 Young's Modulus for a selection of standard and high performance stainless steels using four different techniques ............................................................................................................5–27 Figure 5-10 Thermal conductivity of high performance stainless steel structure types compared with Type 316 stainless steel ........................................................................................................5–27 Figure 5-11 Mean coefficient of thermal expansivity for different high performance stainless steel structure types compared with Type 316 stainless steel (from 20°C to T) ...................................................5–28 Figure 5-12 Corrosion in non-aerated sulphuric acid-chloride solutions - 0.1mm/yr (4mpy) isocorrosion curves ........5–28 Figure 5-13 Critical crevice and pitting corrosion temperatures for stainless steels and nickel alloys ...........................5–29 Figure 5-14 Critical pitting and crevice corrosion temperatures for austenitic stainless steel related to PRE number....5–29 Figure 5-15 Effect of pH and Cl ions on the localised attack of Type 316L stainless steel in SO2 scrubber environments......................................................................................................................5–30 Figure 5-16 Effect of pH and Cl ions on the localised attack of Type 317L stainless steel in SO2 scrubber environments ......................................................................................................................5–31 Figure 5-17 Approximate service limits for stainless steels and nickel-base alloys in flue gas condensates and acid brines at moderate temperatures [60-80°C](140-176°F) ..............................................................5–32 Figure 6-1 Adiabatic saturation curve showing H2SO4 concentration for various temperatures and operating conditions in FGD plant. ................................................................................................................6–5 Figure 6-2 Tensile properties of annealed plate C276 ........................................................................................................6–5 Figure 8-1 Schematic tensile rupture strength in 1000 hours ...........................................................................................8–12 Figure 8-2 Schematic Creep Curve ....................................................................................................................................8–12 Figure 8-3 Short time tensile strengths...............................................................................................................................8–13 Figure 8-4 Stress-rupture curves for several annealed stainless steels - 10,000hrs ..........................................................8–14 Figure 8-5 Stress rupture curves for several stainless steels - 100,000hrs .......................................................................8–14 Figure 8-6 Creep-rate curves for several stainless steels - 1% in 10,000hrs.....................................................................8–15 Figure 8-7 Creep-rate curves for several stainless steels - 1% in 100,000hrs ...................................................................8–15 Figure 8-8 Stress vs rupture-time and creep-rate curves for annealed Type 304 stainless steel........................................8–16 Figure 8-9 Stress vs rupture time and creep-rate curves for annealed Type 309 stainless steel........................................8–16 Figure 8-10 Stress vs rupture time and creep-rate curves for annealed Type 310 stainless steel......................................8–17 Figure 8-11 Stress vs rupture time and creep-rate curves for annealed Type 316 stainless steel......................................8–17 Figure 8-12 Stress vs rupture time and creep-rate curves for annealed Type 321 stainless steel.....................................8–18 Figure 8-13 Stress vs rupture time and creep-rate curves for annealed Type 347 stainless steel......................................8–18 Figure 8-14 Stress vs rupture time and creep-rate curves for annealed Type 410 stainless steel......................................8–19 Figure 8-15 Linear thermal expansion of stainless steels ..................................................................................................8–19 Figure 8-16 Thermal conductivity of stainless steels..........................................................................................................8–20 Figure 8-17 Tensile modulus for ferritic steels (alloy and stainless) .................................................................................8–20 Figure 8-18 Tensile modulus for austenitic stainless steels................................................................................................8–21 Figure 8-19 Comparative scaling behaviour of various steels during 1000-hr exposures in air at temperatures from 1100 to 1700°F (595 tp 925°C) ..................................................................................8–21 Figure 8-20 Corrosion rates for stainless steel in various gases .......................................................................................8–22 Figure 8-21 Effect of nickel on scaling resistance..............................................................................................................8–22
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CICIND Metallic Materials Manual - E
CICIND Metallic Materials Manual - E
1. 1.1
page 1–1
BACKGROUND
General
The Manual has been developed by the CICIND Metallic Materials Committee in order to meet a perceived need for ready reference to the properties and characteristics of metallic materials for use in all aspects of chimney design. Information is well documented but found in diverse locations. In order to facilitate access to information, material data sheets are included in Section 12. Where relevant, sources are referenced in the text, together with a bibliography for further reading. Material specifications are listed with full international designations where applicable, as well as national equivalents wherever possible. Great care was exercised in reproducing the information provided in this Manual to minimise errors. However, it is inevitable that occasional slips may occur and the user is cautioned to exercise care and judgement to interpret the data correctly. Please notify CICIND immediately if you become aware of any errors or omissions so that they may be corrected promptly. Also, we would be pleased to hear of additional sources of information or of additional subjects that may be usefully included in future revisions to the Manual.
1.2
Acknowledgements
The assistance of the Metallic Materials Producers in providing data and directly supporting the work of the Committee and of the Committee members with the encouragement of the CICIND Governing Body is gratefully acknowledged. The Committee Chairman particularly wishes to acknowledge the support of the Nickel Development Institute (NiDI) for whom he acts as a consultant. The Committee comprised: Chairman: W. Plant Members: M. Atkins, M. Beaumont, G. Berger, A. Bhomik, J. Bouten, J. DeMartino, F. Henseler, J. Lettner, W. Mathay, D. Peacock, G. Di Poi, S. Reid, D.T. Smith, J. Sowizal, J. Turner, H. van Koten, R. Warren, T. Warren In preparing this document, great reliance has been placed on published information from a number of sources. The organisations involved include CICIND members, material producers and trade organisations. All such contributions are gratefully acknowledged below.
1.3
Layout of Manual
This Metallic Materials Manual has been prepared in loose format because it is expected that it will be a ‘live’ document and will be updated as more information becomes available. Sections may be individually updated, or new sections, added without having to reprint the entire document. The sections are largely self-contained and, wherever possible, all the information necessary to understand the particular subject is contained within the sections. Figures and Tables for each section are generally included at the end of the section, although occasionally one is included in the main body of the section to facilitate understanding. All Figures and Tables are number sequentially and are listed in the Tables of Content, Tables and Figures at the front of the Manual. Additional supporting data are available in Section 12 from material provided by a selection of manufacturers. These additional data were current at the time of assembly but will, over time, become less up-to-date. Users of this manual are strongly encouraged to seek the most recent data from manufacturers before making final decisions as to material choice.
1.4
Units conversion
To be added
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1.5
Commonly Used Chemical Elements
The elements most commonly encountered in connection with metallic materials, their application and fabrication are given in Table 1-1 below. Name Aluminium Argon Barium Boron Bromine Cadmium Calcium Carbon Chlorine Chromium Cobalt Copper Fluorine Helium Hydrogen Iron Lead Magnesium Manganese Molybdenum Nickel Niobium [Columbium] Nitrogen Oxygen Palladium Phosphorus Potassium Ruthenium Silicon Sodium Sulphur Tin Titanium Tungsten Vanadium Zinc
Symbol Al A Ba B Br Cd Ca C Cl Cr Co Cu F He H Fe Pb Mg Mn Mo Ni Nb [Cb] N O Pd P K Ru Si Na S Sn Ti W V Zn
Table 1-1 Commonly Used Elements
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2.
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INTRODUCTION
Many gaseous products of combustion combined with water vapour form corrosive acids when condensed. Avoidance of condensation, permitting the use of inexpensive materials for containment of flue gases in ducts, flues or chimneys, may be achieved by maintaining high temperatures at the expense of low efficiency of fuel utilisation. Internal surface corrosion problems are magnified when system efficiencies demand lower gas discharge temperatures or flue gas treatment is required such as Flue Gas Desulphurisation or other wet scrubbing process. The external environment may also play a part in causing condensation to the exterior of a chimney. The use, therefore, of the lowest cost metallic material may not be the correct choice. Resisting corrosion is of increasing concern to the chimney designer.
2.1
Acid Dewpoint Corrosion
Dewpoint corrosion can occur when a gas is cooled below the saturation temperature associated with the concentration of condensable corrosive compounds it contains and the formation of acid with water vapour. The recommendation to avoid condensation in a system is to ensure the gas temperature is higher than that of the determined dewpoint temperature by a minimum of about 20°C. This is not always possible, so selection of a material to resist dewpoint corrosion must be considered. The use of corrosion resisting alloys (CRAs) may increase the first cost of the chimney. However, the overall cost of ownership will be significantly reduced by the longer chimney life, reduced maintenance and improved reliability and safety. Methods to establish a chimney’s life cycle cost are available.
2.1.1 Dewpoint Typical atmospheric water vapour levels are between 0.5% and 1%, resulting in a water dewpoint temperature of 0 - 10°C. In comparison, the water dewpoint in a combustion atmosphere containing about 10% moisture is approximately 40°C. Flue gases discharged by wet scrubbers are saturated. The dewpoint temperature is influenced by the presence of other condensable constituents such as sulphur trioxide, hydrogen chloride, traces of hydrogen fluoride, etc., the acidic condensate forming at higher temperatures than water vapour alone. As a flue gas generated by the combustion of a sulphurcontaining fossil fuel is cooled, the first temperature at which sulphuric acid occurs will depend primarily on the partial pressures of sulphur trioxide and water vapour, generally in the range 120-150 °C. At a lower temperature, however, higher than water dewpoint, hydrochloric acid will condense, together with other acid forming compounds with varying acid dewpoint. In the present context “acid dewpoint” refers to the sulphuric acid dewpoint temperature as this is the highest at which acid condensation commences. From Figure 2-1i at a dewpoint of 150°C., the sulphuric acid formed from combination of SO3 + H2O may have a concentration as high as 80%. Sulphuric acid is hygroscopic so that as the temperature falls water is absorbed, diluting the acid concentration. Chimney materials subject to acid dewpoint corrosion must be resistant to a wide range of acid concentrations at temperature.
i
Figure 2-1 Variation of condensed sulphuric acid concentration with temperature; water vapour content of gases approximately 8%
Dewpoint Corrosion: Mechanisms and Solution, Meadowcroft D.B. & Cox W.M., “Dewpoint corrosion”, 1985, Inst of Corr. Sci & Tech.
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2.1.2 Corrosion Most corrosion data published concerning the resistance of materials to sulphuric acid solutions were determined by immersion in bulk acid solutions. These do not relate quantitatively to corrosion resistance in thin film acid environments found on the inner surface of metallic chimneys or liners. In some solutions, such as sulphuric or hydrochloric acid at pH 100
Table 4-1 Limits of exposure to acidic condensation Notes to Table 4-1: 1) The operating hours in Table 4-1 are valid for an SO3 content of 15 ppm. For different values of SO3 content, the hours stated vary inversely with SO3 content. When the SO3 content is not known, chimney design should be based upon a minimum SO3 content equivalent to 2% of the SO2 content in the flue gas. 2) In assessing the number of hours during which a chimney is subject to chemical load, account should be taken of start-up and shut-down periods when the flue gas temperature is below its acid dew point. 3) While a steel chimney may generally be at a temperature above acid dew point, care should be taken to prevent small areas being subject to local cooling and therefore being at risk to localised acid corrosion. Local cooling may be due to: • air leaks • “cold spots” developed by flanges, spoilers or other attachments such as cladding supports • cooling through support points • downdraft effects at the top of the chimney 4) The presence of chlorides or fluorides in the flue gas condensate can radically increase corrosion rates. Estimation of the corrosion rate in these circumstances depends upon a number of complex factors and would require the advice of a corrosion expert in each individual case. However, in the absence of such advice, provided the concentrations of HCl < 30mg/m3 or HF < 5mg/m3 and if the operating time below acid dew point does not exceed 25 hours per year, the degree of chemical load may be regarded as “low”. See Figure 4-2. 5) Regardless of temperatures, chemical load shall be considered “high” if halogen concentrations exceed the following limits: • Hydrogen fluoride:
0.025% by weight (1300mg/m3 at 20 °C and 1 bar pressure).
• Elementary chlorine:
0.1% by weight (1300 mg/m3 at 20 °C and 1 bar pressure).
• Hydrogen chloride:
0.1% by weight (1300 mg/m3 at 20 °C and 1 bar pressure).
6) Saturated or condensing flue gas conditions downstream of a flue gas desulphurisation system shall always be considered as causing “high” chemical load.
4.5
Allowance for Corrosion
The allowances listed in Table 4-2 and Table 4-3 are for a 20 year lifetime of the chimney. For longer planned lifetimes, the corrosion allowances should be increased proportionally. For temporary chimneys, expected to be in service for less
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than one year, values of CE and CI = 0x are permissible, except in conditions of high chemical load, when a corrosion allowance of 3mm is required. For a free-standing chimney with steel liner(s), the internal corrosion allowance only applies to the internal face of the liner(s). The internal face of the outer shell requires no corrosion allowance, provided a weather-tight cover is fitted over the airspace(s) between the liner(s) and the outer shell.
(0.51 mm per yr)
Figure 4-2 Sulphuric acid saturation curve
Painted carbon steel
0mm
Painted carbon steel under insulation/cladding
1mm
Unprotected carbon steel
3mm
Unprotected stainless steel
0mm
Table 4-2 External corrosion allowance (CE) Note: The external corrosion allowances quoted in Table 4-2 are suitable for a normal environment. When a chimney is sited in an aggressive environment, caused by industrial pollution, nearby chimneys or close proximity to the sea, consideration should be given to increasing these allowances.
x
CE = external corrosion allowance, CI = internal corrosion allowance
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Usual temperature of metal in contact with flue gas
Chemical load per Table 3.1
Internal Corrosion Allowance
< 65°C
low
N/A - chemical load always high
medium
N/A - chemical load always high
high
Corrosion allowance inappropriate, use other material
low
1mm
medium
4mm
high
Corrosion allowance inappropriate, use other material
low
1mm
medium
2mm
high
Corrosion allowance inappropriate, use other material
65°C - 345°C
> 345°C
Table 4-3 Internal corrosion allowance (CI) See notes below Notes to Table 4-3: 1)
Provided acid concentration in the condensate is less than 5% and chloride concentration does not exceed 30mg/m3, high molybdenum stainless steel (such as ASTM Type 316L) is suitable within this temperature limit, using a corrosion allowance of 3mm for a 20 year life. These conditions are, however, unlikely to be met in a chimney downstream of a flue gas desulphurisation (FGD) system, generating condensing gases. In these circumstances great care is required in the protection of the gas face of the chimney or its liner, eg. by cladding with a suitable high nickel alloy or titanium or by the application of a suitable organic coating. For further guidance, see the CICIND Chimney Coatings Manual.
2)
In conditions of low chemical load, “Cor-TenTM” steel shows some improvement of corrosion resistance over carbon steel, especially when in contact with condensing acids (SO2/SO3) is intermittent or of short duration (eg. during repeated shut-downs).
3)
In these circumstances, ordinary stainless steels (including high molybdenum stainless steel) have little better corrosion resistance than carbon steel and are, therefore, not recommended. If carbon steel is used in chimneys subject to high chemical load, it will require protection by an appropriate coating. For further guidance, see the CICIND Chimney Coatings Manual.
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APPENDIX 4.1 STRUCTURAL STEELS GUIDANCE ON PROPERTIES FOR FLAT AND LONG PRODUCTS
Tensile strength, N/mm2
0.2% proof stress, N/mm2 Nominal thickness, mm Designation
< 16
16-40
40-63
63-80
80-100
