Handbook Corrosion (1992) WW Part 6 potx

Lithium is somewhat more aggressive to plain carbon steels that sodium or sodium-potassium. As a result, low-alloy steels should not be considered for long-term use above 300 °C (570 °F). At higher temperatures, the ferritic stainless steels show better results at higher temperatures. Cadmium. Low-alloy steels exhibit good serviceability to 700 °C (1290 °F). Zinc. Most engineering metals and alloys show poor resistance to molten zinc, and carbon steels are no exception. Antimony. Low-carbon steels have poor resistance to attack by antimony. Mercury. Although plain carbon steels are virtually unattacked by mercury under nonflowing or isothermal conditions, the presence of either a temperature gradient or liquid flow can lead to drastic attack. The corrosion mechanism seems to be one of dissolution, with the rate of attack increasing rapidly with temperature above 500 °C (930 °F). Alloy additions of chromium, titanium, silicon, and molybdenum, alone or in combination, show resistance to 600 °C (1110 °F). Where applicable, the attack of ferrous alloys by mercury can be reduced to negligible amounts by the addition of 10 ppm Ti to the mercury; this raises the useful range of operating temperatures to 650 °C (1200 °F). Additions of metal with a higher affinity for oxygen than titanium, such as sodium or magnesium, may be required to prevent oxidation of the titanium and loss of the inhibitive action. Aluminum. Plain carbon steels are not satisfactory for long-term containment of molten aluminum. Gallium is one of the most aggressive of all liquid metals and cannot be contained by carbon or low-alloy steels at elevated temperatures. Indium. Carbon and low-alloy steels have poor resistance to molten indium. Lead, Bismuth, Tin, and Their Alloys. Low-alloy steels have good resistance to lead up to 600 °C (1110 °F), to bismuth up to 700 °C (1290 °F), and to tin only up to 150 °C (300 °F). The various alloys of lead, bismuth, and tin are more aggressive. Weathering Steels S.K. Coburn, Corrosion Consultants, Inc.; Yong-Wu Kim, Inland Steel Company The weathering steels had their origin in the early studies of D.M. Buck. After a decade of effort, Buck established the efficacy of copper as a means of enhancing the atmospheric-corrosion resistance of unpainted carbon steel in a variety of environments (Ref 50, 51, 52). While this work was going on, a large study was initiated in 1916 by the American Society for Testing and Materials (ASTM) to evaluate the atmospheric performance of a variety of ferrous materials. By 1929, United States Steel Corporation had initiated studies to enhance the performance of copper-bearing steel further through the addition of a number of alloying elements. By 1933, the first commercially available high-strength low-alloy steel was introduced into the railroad industry for coal hopper car use in the unpainted condition. These high-strength low-alloy steels were capable of resisting the leachates from sulfur-bearing coals better than the existing carbon and copper-bearing steel cars. Since that time, the original architectural grade has been covered by ASTM A 242 (Ref 53). When the heavier structural grades of high-strength low-alloy steels became available, they were covered by ASTM A 588 (Ref 54). Through the exposure of small test panels in various atmospheres, the performance of the steel composition as well as the aggressiveness of the particular location were both calibrated. Other characteristics of the high-strength low-alloy steels were studied, such as the ability to develop the protective oxide film under sheltered conditions in the atmosphere, in the soil, and immersed in freshwater and seawater. Studies were conducted on the staining characteristics and the ability to perform in contact with other materials. Finally, studies were performed to determine the manner in which protective coatings would function. Copper-Bearing Steel To appreciate the nature of the current composition of the weathering steels, it is useful to recall some of Buck's findings. In the early days, scrap steel was not in common use. Thus, Buck accidentally noticed that one test sheet outperformed the others. Upon examination, the copper level of this sheet was found to exceed the 0.01 to 0.02% common to the remainder of the test sheets. This finding resulted in Buck's initiating a series of studies to identify the minimum amount of copper (found to be 0.20%) necessary to effect an improvement in performance and to determine the relationship of the copper content to the sulfur content of the steel. From 1929 to 1933, much effort was expended toward developing compositions with superior atmospheric-corrosion resistance to the accepted 0.20% Cu-containing steels. High-Strength Low-Alloy Steels In 1962, the results of a comprehensive 15.5-year study were published in which some 270 different steels were exposed in three atmospheres beginning in the late 1940s (Ref 22). The sites were at Kearny, NJ (industrial); South Bend, PA (semirural); and Kure Beach, NC (250 m, or 800 ft, from the ocean). Table 5 lists the performance of 18 representative compositions in which the different levels of copper are combined with one of the four alloying elements (nickel, chromium, silicon, and phosphorus) to show their respective influences on corrosion in the industrial and marine sites. In addition, this group contains seven compositions in which one of the alloying elements is omitted, the purpose being to demonstrate how the remaining elements are capable of contributing to a satisfactory performance in the various atmospheres. Figures 6, 7, 8, 9, and 10 in the previous section, "Carbon Steels," in this article also show the effects of the above-mentioned alloying elements on steel corrosion. Table 5 Average reduction in thickness of steel specimens after 15.5-year exposure in different atmospheres Thickness reduction Composition, wt% Kearny, NJ (industrial) Kure Beach, NC, 250-m (800-ft) lot (moderate marine) Specimen No. Cu Ni Cr Si P m mils m mils 1 0.012 . . . . . . . . . . . . 731 28.8 1321 52.0 2 0.04 . . . . . . . . . . . . 223 8.8 363 14.3 3 0.24 . . . . . . . . . . . . 155 6.1 284 11.2 4 0.008 1 . . . . . . . . . 155 6.1 244 9.6 5 0.2 1 . . . . . . . . . 112 4.4 203 8.0 6 0.01 . . . 0.61 . . . . . . 1059 41.7 401 15.8 7 0.22 . . . 0.63 . . . . . . 117 4.6 229 9.0 8 0.01 . . . . . . 0.22 . . . 373 14.7 546 21.5 9 0.22 . . . . . . 0.20 . . . 152 6.0 251 9.9 10 0.02 . . . . . . . . . 0.06 198 7.8 358 14.1 11 0.21 . . . . . . . . . 0.06 124 4.9 231 9.1 12 . . . 1 1.2 0.5 0.12 66 2.6 99 3.9 13 0.21 . . . 1.2 0.62 0.11 48 1.9 84 3.3 14 0.2 1 . . . 0.16 0.11 84 3.3 145 5.7 15 0.18 1 1.3 . . . 0.09 48 1.9 97 3.8 16 0.22 1 1.3 0.46 . . . 48 1.9 94 3.7 17 0.21 1 1.2 0.48 0.06 48 1.9 84 3.3 18 0.21 1 1.2 0.18 0.10 48 1.9 97 3.8 Source: Ref 22 The significance of copper levels is shown in compositions 1, 2 and 3 in Table 5. Compositions 4 and 5 show how nickel can compensate for a low copper level. In contrast, compositions 6 and 7 show that chromium requires copper except in the marine environment. In compositions 8 and 9, silicon shows useful properties in the absence of copper. Phosphorus also contributes to this effect (compositions 10 and 11). Compositions 12 through 18 show the results of combining all of the alloying elements or omitting one of the elements. Additional research revealed that lower concentrations of the alloying elements were still effective. The current compositions of two of the major suppliers are shown in Table 6. Other proprietary compositions can be found in Ref 55. Table 6 Representative compositions of A588 high-strength low-alloy steel Composition, wt% (a) Proprietary grade C Mn P S Si Cu Ni Cr V USS COR-TEN 0.19 (a) 0.80-1.25 0.04 (a) 0.05 (a) 0.30-0.65 0.25-0.40 0.40 (a) 0.40-0.65 0.02-0.10 Mayari R 0.20 (a) 0.75-1.35 0.04 (a) 0.05 (a) 0.15-0.50 0.20-0.40 0.50 (a) 0.40-0.70 0.01-0.10 (a) Maximum. Corrosion Behavior Under Different Exposure Conditions The standard method for developing typical corrosion rates for comparative purposes is to expose 100- × 150-mm (4- × 6- in.) panels on test racks at an inclination of 30° from the horizontal facing south. An exposure rack with a sulfur dioxide candle in a louvered box is shown in Fig. 15. More detailed information on atmospheric-corrosion testing can be found in the article "Simulated Service Testing" in this Volume. Fig. 15 Typical exposure rack with sulfur dioxide candle in louvered box The panel performance is judged by the loss in weight sustained after varying exposure periods. The relationship between the loss in weight sustained by the skyward surface and the groundwater surface by exposing test panels in semirural South Bend, PA, and industrial Kearny, NJ, for 4 years was first reported in Ref 56. In this test, carbon steel, copper- bearing steel, and USS COR-TEN steel panels were exposed. In both environments, the contribution to the total weight loss of the test panels was essentially the same. The skyward surface that was washed by the rain and warmed by the wind and sun contributed 37% to the weight loss, while the groundward surface that was never washed by the rain nor dried as much by the sun contributed 63% to the weight loss. This is significant because the sheltered surface has a coarse granular oxide film due to the loosely attached initial oxide film that tends to retain dampness and to promote additional corrosion. Another study was conducted to compare the loss in weight between a vertical panel and an inclined panel in three different environments using copper-bearing steel and copper-free steel (Ref 57). It is apparent from the data discussed in Table 7 that a vertical surface that is only occasionally washed by rain is likely to corrode approximately 20 to 25% more than an inclined surface. Table 7 Relative corrosivity of panels in vertical and inclined positions in different environments Reduction in thickness after 2 years Copper-free Copper-bearing Location and environment Position m mils Ratio m mils Ratio Vertical 105 4.12 88 3.45 Kearny, NJ (industrial) Inclined 84 3.30 1.25 70 2.76 1.25 Vertical 116 4.55 102 4.02 Vandergrift, PA (industrial) Inclined 95 3.73 1.22 81 3.20 1.25 Vertical 57 2.26 55 2.18 South Bend, PA (semirural) Inclined 50 1.95 1.16 46 1.81 1.20 Source: Ref 57 Because some weathering steels are licensed in many countries in Europe and the Far East, comparisons sometimes are made in which it is stated that poor results may occur because of some reduced performance level or excessive time interval before the protective oxide coating has matured in these different countries. What is often overlooked is that most European countries are located in latitudes that range from the equivalent Canadian border to the Arctic Circle. The sun is lower and the hours of sunlight are fewer than in the continental United States; thus, the time of wetness is longer (Table 8). Table 8 Latitudes of North American and European countries Latitude U.S. Canadian (a) Italy France Germany England Scandinavia From 30° 45° 40° 45° 46° 52° 55° To 45° 55° 45° 50° 53° 57° 70° (a) Most densely populated area Characteristics of the Protective Oxide Film It is likely that rusting occurs more during the night when atmospheric moisture condenses on metal surfaces when the dew point is reached. On average, in the Midwest and middle Atlantic states up through Canada, a 5.5- to 8.3- °C (10- to 15- °F) drop in temperature when the daytime relative humidity is around 75% is sufficient to result in condensation at night. The moisture absorbs the gaseous contaminants of the local atmosphere and nucleates around a dust particle and thus brings an acidic droplet to the metal surface. The thin acidic moisture film is capable of solubilizing the steel and initiating the rusting or oxidizing process. By morning, the sun and the moving air dry the gelatinous ferric hydroxide compounds that form, and the oxide begins to consolidate itself on the surface. This alternate wetting and drying cycle produces the protective oxide film on weathering steel compositions, but it produces the more porous nonprotective oxide film on carbon steel. Repeated cycles of this type ultimately result in complete coverage of the surface and a slowing of the corrosion rate. This behavior can best be expressed by time/corrosion curves, as shown in Fig. 16. Fig. 16 Time/corrosion curves showing relative performance in a semi-industrial environment It should be noted that the formation of a protective rust film can result in a deceleration, although not necessarily a cessation, of corrosion. However, as the alloying increases, the quality of protection increases, as evident with the weathering steel composition. There are a number of ways of demonstrating this improving condition. A practical test is that demonstrated with rusted test panels that are evaluated for their wicking tendency after various exposure periods. Table 9 contains the results of a wicking test in which the edge of a test panel contacts the surface of a dish containing water. The height of wicking is an indication of the compactness of the protective oxide film. Table 9 Height of wicking of exposed steel panels USS COR-TEN steel Carbon steel Exposure period, years mm in. mm in. 0.5 25.4 1.0 48.0 1.89 1.0 19.0 0.75 41.5 1.63 2.0 1.6 0.063 31.7 1.25 4.0 1.6 0.063 14.2 0.56 It is easy to understand the sealing action that occurs as the oxide film ages by virtue of the behavior of a drop of water applied to the surface of a rusted test panel. The water droplet on a weathering steel panel retains its spherical form because of the sealed surface (Fig. 17). In contrast, the porous rust film on the carbon steel panel permits the droplet to wet out and penetrate the rust film. Fig. 17 Water droplet wetted out and penetrated carbon steel rust (left) but failed to penetrate sealed rust of weathering steel (right) As indicated earlier, the key to the development of the protective oxide film is the alternate wetting and drying cycle typified by the normal night and day exposure. Under conditions of long-term immersion in freshwater or seawater, the corrosion rate is the same as that for carbon steel about 0.13 mm/yr (5 mils/yr). Similarly, burial in soil having varying moisture levels will result in behavior similar to that of carbon steel. The lack of a drying cycle inhibits the formation of the characteristic oxide film. The implication then is to avoid features in any structure, such as pockets, that can retain water for lengthy periods and to paint any portion of a structure, such as a column, that will be in the soil subject to rain and snow drainage. To illustrate the results of constant dampness, a sheet of copper-bearing steel was exposed on a 30° test rack (Ref 26). The bottom of the sheet was turned up to serve as a trough to retain rainwater. The top of the sheet was turned down on the back of the rack to serve as a vertical wall facing north. The failure time in months in terms of severe rusting is shown in Table 10. It is clearly evident from the service life of the bottom and the sides of the trough that long-term dampness has a deleterious effect on the steel. It is also significant that the lack of the drying effect of the sun and the lack of the washing effect of the rain have combined to limit the service life of the vertical portion facing the north. The ideal exposure conditions are those in which the surface is washed frequently to remove contaminants and the sun is present to dry the surface. Table 10 Failure time for copper-bearing steel sheet Sheet face Months to severe rust Performance ratio Bottom of trough 25 1 Sides of trough 25 1 Vertical portion facing north 130 5.2 Inclined skyward surface facing south 170 6.8 Case Histories and Design Considerations Thus, from the data presented in this section, the working rules for creating optimum conditions for the formation of the protective oxide film have evolved. The following case histories illustrate both the violations of these rules and suggestions on how to avoid certain maintenance problems. Example 1: Assessing the Influence of Location. The Gulf Coast, where onshore breezes are the rule, experiences considerable penetration of salt air because there are no forested areas or concentration of tall buildings to provide a snow fence effect to deflect the incoming breezes upward. Thus, structures are prone to impact by salt-laden air, permitting a buildup of a salt residue that can inhibit formation of the characteristic oxide film. To assess a location properly, one should expose a small test rack for 18 to 24 months with panels of weathering steel and copper-bearing steel or carbon steel with less than 0.02% Cu. Two or three removals for weight loss determination will indicate whether a protective oxide is forming on the weathering steel. If proximity to the ocean is a question, then exposure of a chloride candle, either at ground level or preferably at an elevation comparable to the height of the structure, should be made, and the monthly chloride determinations should be performed for at least 12 months in order to assess the influence of the seasons. Example 2: Storage and Stacking of Weathering Steels. Electrical utilities store their tower angles at a central or regional location and along a power-line site. In either case, angles should be stored facedown rather than nesting faceup. This eliminates the possibility of retaining water in between nested members. They should be stored on small steel angles with one end of the bundles elevated to facilitate drainage. When angles or channels are nested so that they can retain water, a loose voluminous rust scale develops, as seen in Fig. 18. Fortunately, such a scale can be readily removed by hammering, brushing, or with a power-driven wire wheel. Fig. 18 View of loosely attached rust scale that formed among nested angles in a utility storage yard Large girders, H-beams, and channels are often nested for economical stacking. These should also be stacked with one end elevated and resting on steel angles. All configurations should facilitate drainage and minimize retention of rainwater. Draping with a cover cloth is preferred when space restrictions require that nesting be done. Before heavy girders and columns are erected, they should be inspected by hammering to ensure that a laminated sheet of rust has not formed during the storage period. If this inspection is not performed, the rusted slab will begin to delaminate once in place, and this will raise questions as to whether the steel is truly of the weathering composition. Example 3: Galvanic Corrosion Problems. Care must be exercised in preventing the mixing of carbon steel with a weathering steel stock. When a missing member is encountered, the erection crews may substitute a carbon steel member. This may go unnoticed for several years and then result in excessive deterioration, such as that shown in Fig. 19. Fig. 19 Results of mixing carbon steel angle in a weathering steel structure One of the more vivid examples of galvanically coupled metals is the use of the hanger pin detail shown in Fig. 20 to facilitate girder movement during expansion and contraction. In this case, a bronze washer is part of the assembly. When such a device is used in the snow-belt states, it can create a strong galvanic cell with the steel when deicing salt solution drains from the deck through the expansion joint and through the crevice created by the connection. The outcome can be corrosion of the steel, with the resulting rust formation freezing and therefore immobilizing the joint. The resulting corrosion is evident in Fig. 21. Fig. 20 Typical hanger pin assembly with bronze washer [...]... Research, Dec 1981 44 D.A Lewis, Some Aspects of the Corrosion of Steel in Concrete, in Proceedings of the First International 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 Congress on Metallic Corrosion, National Association of Corrosion Engineers, 1 961 , p 547-555 J Ishikawa, B Bresler, and I Cornet, Electrochemical Study of the Corrosion Behavior of Galvanized Steel in Concrete,... Society for Metals, 1942 36 C.P Larrabee, U.S Patent 2,315,1 56, 1943 37 J.T Crennell, in Corrosion, Vol 1, L.L Shreir, Ed., John Wiley & Sons, 1 963 , p 2.34 38 F.L LaQue, in The Corrosion Handbook, H.H Uhlig, Ed., John Wiley & Sons, 1948, p 391 39 K.H Logan, Corrosion by Soils, in The Corrosion Handbook, H.H Uhlig, Ed., John Wiley & Sons, 1948, p 4 46- 466 40 M Romanoff, "Underground Corrosion, " NBS Circular... Metallic Corrosion, National Association of Corrosion Engineers, 1972, p 59 860 1 "Solving Rebar Corrosion Problems in Concrete," Seminar, Chicago, Il, National Association of Corrosion Engineers, Sept 1982 M Hecht, W.C Schroeder, E.P Partridge, and S.F Whirl, Boiler Corrosion, in The Corrosion Handbook, H.H Uhlig, Ed., John Wiley & Sons, 1948, p 520-537 D.M Buck, Copper in Steel The Influence on Corrosion, ... Swelling of Zinc-Aluminum Alloys, Trans Am Inst Min Metall Eng., Vol 60 , 1923, p 7 96 H.H Lee, Galvanized Steel With Improved Resistance to Intergranular Corrosion, Proc Galvanized Committee, Vol 69 , 1977, p 17 H.H Uhlig, Corrosion and Corrosion Control, John Wiley & Sons, 1971, p 335 69 70 71 72 J.H Rigo, Corrosion, Vol 17 (No 5), 1 961 , p 245 J.E.O Mayne, Anti-corros., Oct 1973, p 3-8 N.C Fawcett, Polymer... First International Congress on Metallic Corrosion, Butterworths, 1 962 , p 2 76- 285 23 C.P Larrabee, Corrosion Resistance of High Strength Low Alloy Steels as Influenced by Composition and Environment, Corrosion, Vol 9 (No 8), 1953, p 259-271 24 R.A Legault and A.G Preban, Kinetics of the Atmospheric Corrosion of Low-Alloy Steels in an Industrial Environment, Corrosion, Vol 31 (No 4), 1975, p 117-122... an air-water environment (Ref 66 ) The adverse effect of intergranular corrosion of hot-dip galvanized steel was first observed in 1 963 , and was investigated at Inland Steel Company in 1972 (Ref 67 ) The observed effect associated with intergranular corrosion was termed delayed adhesion failure Delayed adhesion failure is a deterioration in coating adhesion due to selective corrosion at grain boundaries... STP 64 6, American Society for Testing and Materials, 1978 Metal Corrosion in the Atmosphere, STP 435, American Society for Testing and Materials, 1 968 W.H Ailor, Ed., Atmospheric Corrosion, Wiley-Interscience, 1982 Corrosiveness of Various Atmospheric Test Sites as Measured by Specimens of Zinc and Steel, in Metal Corrosion in the Atmosphere, STP 435, American Society for Testing and Materials, 1 968 ,... Fifth International Congress on Metallic Corrosion, National Association of Corrosion Engineers, 1972, p 775-779 L.L Shreir, Ed., Corrosion, Vol 1, John Wiley & Sons, 1 963 , p 3.8 P.R Grossman, Investigation of Atmospheric Exposure Factors That Determine Time-of-Wetness of Outdoor Structures, in Atmospheric Factors Affecting the Corrosion of Engineering Metals, STP 64 6, S.K Coburn, Ed., American Society... (No 1), 1 965 , p 16 K Tripathi, U.S Agninotui, and J.N Nanda, Br Corros J., Vol 7, 1972, p 212 H Guttman and J.P Sereda, Measurement of Atmospheric Factors Affecting the Corrosion of Metals, in Metal Corrosion in the Atmosphere, STP 435, American Society for Testing and Materials, 1 968 , p 3 26 V Kucera and J Gullmann, "Practical Experience With an Electrochemical Technique for Atmospheric Corrosion Monitoring,"... in Concrete, in Proceedings of the Fourth International Congress of Metallic Corrosion, National Association of Corrosion Engineers, 1972, p 5 56- 559 I Medgyesi, Problems Related to the Corrosion of Reinforcing Rods in Concrete, in Proceedings of the Fourth International Congress on Metallic Corrosion, National Association of Corrosion Engineers, 1972, p 591-593 B Heuze, Cathodic Protection for Reinforced . 223 8.8 363 14.3 3 0.24 . . . . . . . . . . . . 155 6. 1 284 11.2 4 0.008 1 . . . . . . . . . 155 6. 1 244 9 .6 5 0.2 1 . . . . . . . . . 112 4.4 203 8.0 6 0.01 . . . 0 .61 . 0.21 . . . . . . . . . 0. 06 124 4.9 231 9.1 12 . . . 1 1.2 0.5 0.12 66 2 .6 99 3.9 13 0.21 . . . 1.2 0 .62 0.11 48 1.9 84 3.3 14 0.2 1 . . . 0. 16 0.11 84 3.3 145 5.7. in. mm in. 0.5 25.4 1.0 48.0 1.89 1.0 19.0 0.75 41.5 1 .63 2.0 1 .6 0. 063 31.7 1.25 4.0 1 .6 0. 063 14.2 0. 56 It is easy to understand the sealing action that occurs as