Handbook Corrosion (1992) WW Part 14 pdf

Classifiers blades . . . Ni-Hard type 4 Ore chutes Impact, gouging, abrasion, pH 6-8 Ni-Hard, nickel-containing manganese steel Scrapers Impact loading, gouging, abrasion Cast ASTM A579 steel, Ni-Hard cast iron, hard cast irons Wire rope Corrosive-abrasive, pH 2-12 Kevlar, steel wire rope Piping Corrosive-abrasive Type 316 stainless steel, CN-7M, Ni-Hard cast irons, rubber covered fiberglass- reinforced plastic Scrubbers Off-gas products High-grade nickel alloys Chain conveyors Corrosive-abrasive Plated (nickel, cadmium, or zinc) steels References 1. G.R. Hoey and W. Dingley, Corrosion Control in Canadian Sulfide Ore Mines and Mills, Can. M in. Metall. Bull., Vol 64, May 1971, p 1-8 2. G.J. Biefer, Corrosion Fatigue of Structural Metals in Mine Shaft Waters, Can. Min. Metall. Bull., Vol 58, June 1967, p 675-681 3. N.S. Rawat, Corrosivity of Underground Mine Atmospheres and Mine Waters: A Re view and Preliminary Study, Br. Corros. J., Vol 11 (No. 2), 1976, p 86-91 4. I. Iwasaki, K.A. Natarajan, S.C. Riemer, and J.N. Orlich, Corrosion and Abrasive Wear in Ore Grinding, in Wear of Materials 1985, American Society of Mechanical Engineers, 1985, p 509-518 5. T.P. Beckwith, Jr., The Bacterial Corrosion of Iron and Steel, J. Am. Water Works Assoc., Vol 33 (No. 1), June 1941, p 147-165 6. B. Intorre, E. Kaup, J. Hardman, P. Lanik, H. Feiler, S. Zostak, and W.E. Rinne, Complete Water Reuse Industrial Opportunity, in Proceedings of the National Conference, American Institute of Chemical Engineers, 1973, p 88 7. F.N. Speller, Corrosion: Causes and Prevention, McGraw-Hill, 1951, p 208 8. S.L. Pohlman and R.V. Olson, "Corrosion and Material Problem in the Copper Production Industry," Paper 229, presented at Corrosion/84, National Association of Corrosion Engineers, 1984 9. K. Adam, K.A. Natarajan, S.C. Riemer, and I. Iwasaki, Electrochemical Aspects of Grinding Media Mineral Interaction in Sulfide Ore Grinding, Corrosion, Vol 42 (No. 8), 1980, p 440-446 Wire Rope Mine shaft depths of 1830 m (6000 ft) are not uncommon; gold mines in South Africa approach depths of 2285 m (7500 ft) (Ref 10). The hoisting equipment used in these mines, especially ropes, on which lives of personnel depend, is subjected to the corrosive environment of the mines. Although wear is also a factor, corrosion is perhaps the most serious aspect of mine safety. Corrosion is difficult to evaluate and is a more serious cause of degradation than abrasion (Ref 11). If corrosion is evident, the remaining strength cannot be calculated with safety, nor is there any reasonable way to determine whether or not the rope is safe except by the judgement of the inspector. Statistical analysis from the results of rope tests on mine-hoist wire ropes has shown that 66% of the ropes exhibited the greatest strength loss in the half of the ropes nearest the conveyance (Ref 12). This is the portion of the rope that is in contact with the shaft environment during most of its service life. Replacement of hoist rope is a routine procedure in most mines and is suggested every 18 to 36 months, depending on the mine environment and use (Ref 1, 13). Some regulatory agencies will not allow the use of a shaft rope on which marked corrosion is evident (Ref 11). Adequate service life of hoist rope is economically desirable. Therefore, the composition of present-day hoist rope has been extensively studied. Carbon steel strand wire has competition from such substitute materials as stainless steel (Ref 14) and synthetic fibers (Ref 15). Austenitic stainless steel rope (15.5 to 18.5% Cr and 11 to 13% Ni) is available and has endurance strength of 72 to 83% of that of carbon steel wire. Much can be said for synthetic fiber rope construction. For example, Aramid fiber rope has exceptional strength-to-weight ratios, outstanding tension-tension-fatigue performance (Ref 15), and excellent corrosion resistance. Roof Bolts Roof bolts are extensively used for roof support in underground mines. More than 120 million roof bolts are used per year in the United States mining industry (Ref 11). Roof bolts made of low-carbon steel in a number of design variations are subject to corrosion attack in the mine environment. In sulfide mines, the roof bolts have been reported to fail within 1 year by breaking at a distance of approximately 355 mm (14 in.) inside the drill hole (Ref 1). This roof bolt failure has been related to stress-corrosion cracking. Roof falls are associated with such roof bolt failures. Pump and Piping Systems Corrosion in pump and piping systems is well known in the mining and mineral-processing industries. The first indication of pump corrosion is that the pump no longer meets the flow demands of capacity and head requirements. Also, the external surfaces are corroded and encrusted with corrosion product. Because recognition of corrosion type is so important in diagnosing corrosion problems and their prevention and because published information on case histories is scarce, corrosion types will be discussed and illustrated in the following sections in this article. Uniform Corrosion. The most common form of pump corrosion is characterized by uniform attack on the entire exposed surface. Figure 1 shows uniform corrosion on a stainless steel pump impeller that was exposed to 50% phosphoric acid (H 3 PO 4 ) and 10% gypsum pumping fluid for approximately 1 year. Figure 2 shows uniform corrosion due to potash brine on a cast (hard) iron pump runner. Fig. 1 Uniform corrosion of ACI CD- 4MCu cast stainless steel pump impeller after 1 year in an environment containing 50% H 3 PO 4 and 10% gypsum. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Fig. 2 Uniform corrosion of an abrasion-resistant iron pump runner that contacted potash brine slurry. (a) End view. (b) Side view. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Pitting corrosion on an Alloy Casting Institute (ACI) CF-8M stainless steel casting pump case is illustrated in Fig. 3. This pump case, which was exposed to low pH and high Cl - concentration, failed after approximately 3 years of service. Fig. 3 Pitting corrosion of an ACI CF- 8M stainless steel pump case used to pump a nickel plating solution with a high concentration of Cl - and a high operating temp erature. This damage occurred during 3 years of service. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Erosion-corrosion of an ACI CN-7M stainless steel cast impeller after exposure to hot concentrated H 2 SO 4 with solids present is shown in Fig. 4. Erosion-corrosion is evident in Fig. 5, which shows that the erosion-corrosion damage increased on the portion of the impeller that had the greatest fluid velocity. This impeller, cast from an abrasion-resistant while iron, was used to pump fluids containing 30% solid (iron ore tailings) at a pH of 11.2. Fig. 4 Erosion-corrosion of ACI CN-7M stainless steel pump components that pumped hot H 2 SO 4 with some solids present. Note the grooves, gullies, waves, and valleys common to erosion-corrosion damage. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Fig. 5 Erosion-corrosion of an abrasion- resistant iron pump runner used to pump 30% iron tailings in a fluid with a pH of 11.2. This runner had a service life of approximately 3 months. Note that most of the damage is on the outer peripheral area of the runner where fluid velocity is the highest. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Crevice Corrosion. Figure 6 shows crevice corrosion on an ACI CF-8M cast stainless steel pump case that was gasket sealed on the discharge flange. Attack is evident in the region where the gasket was placed. It is important to design mining and milling equipment for easy drainage and cleaning in order to prevent the buildup of stagnant water that will produce concentration cells and lead to crevice corrosion and pitting. Figure 7 illustrates both poor and improved design for avoidance of localized attack. More information on proper design is available in the article “Designing to Minimize Corrosion” in Corrosion: Fundamentals, Testing, and Protection, Volume 13A of ASM Handbook. Fig. 6 Crevice corrosion at the intake flange of an ACI CF- 8M stainless steel pump case. Notice that the corrosion damage occurred under the gasket. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Fig. 7 Poor and improved engineering design to avoid crevice corrosion. Source: Ref 16 Intergranular corrosion is common to stainless steel pump castings. Figure 8 shows the excessively attacked grain boundaries. A quick test to identify this type of corrosion is to peen the pump casting with a small hammer. Loss of acoustical properties is evidence of intergranular grain-boundary attack, especially in sensitized stainless steel castings. A form of intergranular corrosion associated with weld deposits that is commonly called weld decay is shown in Fig. 9, which illustrates a field-weld repair of an ACI CN-7M stainless steel impeller that was not postweld heat treated (solution annealed and quenched) to restore corrosion resistance. This weld-repaired casting was exposed to a phosphoric anhydride (P 2 O 5 ) solution at 80 °C (175 °F). It is evident that the weld decay occurred in the heat-affected zone of the weld deposit. Fig. 8 Intergranular corrosion of an ACI CN-7M stainless steel pump component that contacted HCl-Cl 2 gas fumes. Note the grain-boundary attack. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Fig. 9 Weld decay of an ACI CN-7M stainless steel pump impeller that was field weld re paired with no postweld heat treatment. The pump service was P 2 O 5 solution at 80 °C (175 °F). (a) Overall view of impeller. (b) Closeup view of the weld repair and the associated weld decay, which occurred adjacent to the weld deposit. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Dealloying. Figure 10 shows selective leaching (dealloying) of a high-nickel cast iron. The physical dimension of the pump component remained constant, while porous, selectively leached regions grew into the casting. This porous layer consists of residual graphite contained in the cast iron and corrosion product. This pump component was exposed to fluosilicic acid (H 2 SiF 6 ) and failed after 12 days of service. Fig. 10 Selective leaching of a cast iron pump impeller after 12 days of service in H 2 SiF 6 . Section through the impeller shows the selectively leached layer, which contains graphite and corrosion product. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Galvanic corrosion between two stainless steels is illustrated in Fig. 11. These AISI type 304 stainless steel stud bolts held together an Alloy 20 (ACI CN-7M) pump housing. The bolts became anodic to the housing in 45% H 2 SO 4 and subsequently failed. Table 4 lists various combinations of pump an valve trim materials and indicates the combination that may be susceptible to galvanic attack. Table 4 Galvanic compatibility of materials used for pump components Trim Body material Brass or bronze Nickel- copper alloy Type 316 Cast iron Protected Protected Protected Austenitic nickel cast iron Protected Protected Protected M or G bronze 70-30 copper nickel May vary (a) Protected Protected Nickel-copper alloy Unsatisfactory Neutral May vary (b) Alloy 20 Unsatisfactory Neutral May vary (b) (a) Bronze trim commonly used. Trim may become anodic to body if velocity and turbulence keep stable protective film from forming on seat. (b) Type 316 is so close to nickel- copper alloy in potential that it does not receive enough cathodic protection to protect it from pitting under low-velocity and crevice conditions. Fig. 11 Galvanic corrosion of AISI type 304 stainless steel stud bolts that fastened two Alloy 20 (ACI CN- 7M) pump components. The pump was pumping 45% H 2 SO 4 at 95 °C (200 °F). The stud bolts were anodic to the Alloy 20 pump housings. Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Cavitation is a familiar term within the industry. The causes are also familiar; principally, there is a lack of net positive suction head, which is the suction pressure that should be available to the pump for correct performance. Cavitation usually manifest itself by another familiar pump characteristic noise. The buildup and subsequent collapse of bubbles on the impeller create the familiar popcorn noise. The effects of cavitation (the violent collapse of bubbles) are illustrated in Fig. 12 and 13. Plastic and metal impellers have been found to be susceptible to cavitation damage. A contributing cause of cavitation has been found to be plugged filters on the intake (suction)side of the pump, coupled with the marginal net positive suction head available to the pump. Table 5 lists engineering materials based on their resistance to cavitation damage. Table 5 Rating of materials for cavitation resistance Most resistant Stellites 17Cr-7Ni stainless steel welding rod 18-8 stainless steel welding rod Bronze welding rod (Cu-10Al-1.5Fe) 25Cr-20Ni weld Eutectic-Xyron 2-24 weld Ampco bronze casting 18-8 cast stainless steel Nickel-aluminum bronze, cast 13% Cr cast iron Manganese bronze, cast 18-8 stainless steel spray metallizing Cast steel Bronze Rubber Cast iron Aluminum Least resistant Source: Ref 17 Fig. 12 Cavitation damage of phenolic plastic pump impeller. Note the craterlike depression on the damaged surface caused by the collapse of bubbles on the impeller surface. Courtesy of A.R. Wilfley & So ns, Inc., Pump Division Fig. 13 Cavitation damage of an ACI CN-7M stainless steel pump impeller that pumped NH 4 NO 3 solution a t 140 °C (280 °F). Courtesy of A.R. Wilfley & Sons, Inc., Pump Division Figure 12 shows the craterlike damage caused by cavitation on a plastic impeller. Figure 13 shows cavitation damage on an ACI CN-7M stainless steel impeller that pumped hot ammonium nitrate (NH 4 NO 3 ); the pumping installation had a total lack of a net positive suction head. Erosion-Corrosion. During mill processing, fluids are pumped containing particulates that are usually carried in a corrosive medium. Pumping this slurry promotes erosion-corrosion in piping, tanks, and pumps. Erosion-corrosion is a function of the fluid velocity and the nature of the particulates and fluid. The following procedures can be used to reduce erosion-corrosion or to increase the service lives of piping and pumping systems: • Increase the thickness of pipes • Use larger inside diameter pipes to reduce fluid velocity for the transport of a specific fluid volume • Streamline bends in piping to ensure laminar flow • Use nonmetallic ferrules inserted in the inlet ends of pipes • Design for easy replacement of parts that experience severe erosion-corrosion • Use coatings that produce an erosion-corrosion resistant barrier, such as rubber coatings (Ref 18) Material selection is an important consideration for erosion-corrosion resistance. Alloy hardness has also been shown to be a factor in erosion-corrosion resistance. Generally, soft alloys are more susceptible to erosion-corrosion than their harder counterparts, but the relative hardness properties of the alloy can be misleading, because the hardening mechanism affects resistance to erosion-corrosion (Ref 8). For example solid-solution hardening has been found to offer greater resistance than that provided by conventional heat treatment. One example of this is the cast precipitation-hardening alloy ACI CD-4MCu, which outperforms Alloy 20 (CN-7M) and austenitic stainless steels in many applications. Economics often enters into material selection. Cast iron is relatively more economical and frequently exhibits better erosion-corrosion resistance than cast steel. High-silicon cast iron (14.5% Si) has been found to be an economical selection. Active-passive materials, such as stainless steels and titanium, owe their corrosion resistance to their developing a protective passive oxide film. This protective film, however, can be continuously damaged by erosive-abrasive processes. Selection of passive alloys should be based only on experience and/or laboratory test results. Joints must be reliable. Welded pipe, such as carbon steel or stainless steel, is free of flanges but is costly to install. Nonwelded joints are susceptible to crevice corrosion; therefore, stainless steel, in particular, will not attain its expected service life. References cited in this section 8. S.L. Pohlman and R.V. Olson, "Corrosion and Material Problem in the Copper Production Industry," Paper 229, presented at Corrosion/84, National Association of Corrosion Engineers, 1984 16. R.F. Steigerwald, Corrosion Principles for the Mining Engineer, in Symposium Materials for Mining Industry, AMAX Molybdenum, Inc. 1974 17. M.G. Fontana and N.D. Greene, Corrosion Engineering, McGraw-Hill, 1967 18. L.D. Eccleston, Protective Coatings in the Mining Industry, Can. Min. Metall. Bull., Vol 72 (No. 3), 1979, p 170-173 Tanks Most tanks are made from low-carbon steel for economic considerations. The most common corrosion protection for these tanks is the use of coatings and linings. Cathodic protection can also be used and in commonly employed in conjunction with a coating (Ref 18). Coating materials can be classified as cement, epoxy, epoxy-phenolic, neoprene, latex, sprayed polyresin coating, polyesters and vinyl esters (heavy coatings), and baked phenolic. Steel tanks are also lined with natural rubber, synthetic elastomers, rubber-backed polypropylene, and glass. Glass lining would require an oven bake. Stainless steel and titanium alloys have also been used for tanks. Their use depends on their specific corrosion resistance to the solution. Selection of an alloy type becomes a question of economics. Reactor Vessels A variety of materials are used, depending on the corrosivity of the media being contained. With neutral or alkaline pH, carbon steels are often used. With increasing corrosivity, consideration is first given the austenitic stainless steels, then iron-nickel-chromium superalloys, and finally nickel-base superalloys. For special environments, copper, copper-nickel, and nickel-copper (Monel-type) alloys are used (Ref 19). Titanium is known to have excellent corrosion resistance in some of the most aggressive solutions. Cyclic Loading Machinery The mining and mineral industry use large numbers of rotary and cyclic loaded equipment. This equipment is subject to fatigue and corrosion fatigue. Table 6 illustrates the significant reduction of fatigue strength of various materials that were tested in mine water and compared to fatigue strength in air. This problem can be reduced by designing heavier sections into the part to reduce load and by applying protective coatings (Ref 18). Table 6 Fatigue and corrosion fatigue strengths of various alloys at 10 7 cycles Corrosion fatigue strength Fatigue strength In Levack water In Helen water In Leitch water Metal MPa ksi MPa ksi MPa ksi MPa ksi T1 tool steel 414 60 131 19 145 21 152 22 Abrasion-resistant steel 307 44.5 152 22 145 21 124 18 Low-carbon steel 214 31 152 22 159 23 138 20 Stelcoloy-G steel 269 39 138 20 114 16.5 124 18 Aluminum alloy 6061-T6 107 15.5 69 10 107 15.5 55 8 References 1. G.R. Hoey and W. Dingley, Corrosion Control in Canadian Sulfide Ore Mines and Mills, Can. Min. Metall. Bull., Vol 64, May 1971, p 1-8 2. G.J. Biefer, Corrosion Fatigue of Structural Metals in Mine Shaft Waters, Can. Min. Metall. Bull., Vol 58, June 1967, p 675-681 3. N.S. Rawat, Corrosivity of Underground Mine Atmospheres and Mine Waters: A Review and Preliminary Study, Br. Corros. J., Vol 11 (No. 2), 1976, p 86-91 4. I. Iwasaki, K.A. Natarajan, S.C. Riemer, and J.N. Orlich, Corrosion and Abrasive Wear in Ore Grinding, in Wear of Materials 1985, American Society of Mechanical Engineers, 1985, p 509-518 5. T.P. Beckwith, Jr., The Bacterial Corrosion of Iron and Steel, J. Am. Water Works Assoc., Vol 33 (No. 1), June 1941, p 147-165 6. B. I ntorre, E. Kaup, J. Hardman, P. Lanik, H. Feiler, S. Zostak, and W.E. Rinne, Complete Water Reuse Industrial Opportunity, in Proceedings of the National Conference, American Institute of Chemical Engineers, 1973, p 88 7. F.N. Speller, Corrosion: Causes and Prevention, McGraw-Hill, 1951, p 208 8. S.L. Pohlman and R.V. Olson, "Corrosion and Material Problem in the Copper Production Industry," Paper 229, presented at Corrosion/84, National Association of Corrosion Engineers, 1984 9. K. Adam, K.A. Natarajan, S.C. Riemer, and I. Iwasaki, Electrochemical Aspects of Grinding Media Mineral Interaction in Sulfide Ore Grinding, Corrosion, Vol 42 (No. 8), 1980, p 440-446 10. S.A. Bryson, Repair Work and Fabrication in Gold Mining Environments, FWP J., Vol 24 (No. 2), 1984, p 35-48 11. J.M. Karhnak, "Corrosion and Wear Problems Associated With the Mining and Mineral Processing Industry," Paper 230, presented at Corrosion/84, National Association of Corrosion Engineers, 1984 12. R.L. Jentgen, R.C. Rice, and G.L. An derson, Preliminary Statistical Analysis of Data From Ontario Special Rope Tests on Mine-Hoist Wire Ropes, Can. Min. Metall. Bull., Vol 77 (No. 11), 1984, p 50-54 13. H. Precek and J. Zeigler, Ropes for Use at Great Depths in Mining, Wire Ind., Vol 52 (No. 8), 1985, p 486- 487 14. H. Hartmann, Hauling Ropes for Shaft Installations Under Extreme Corrosive Conditions, Wire Ind., Vol 46 (No. 3), 1979, p 179 15. N. O'Hear, Developments in Aramid Fibre Ropes, Wire Ind., Vol 49 (No. 11), 1982, p 845-850 16. R.F. Steigerwald, Corrosion Principles for the Mining Engineer, in Symposium Materials for Mining Industry, AMAX Molybdenum, Inc. 1974 17. M.G. Fontana and N.D. Greene, Corrosion Engineering, McGraw-Hill, 1967 18. L.D. Eccleston, Protective Coatings in the Mining Industry, Can. Min. Metall. Bull., Vol 72 (No. 3), 1979, p 170-173 19. A.I. Asphahani and P. Crook, "Corrosion and Wear of High Performance Alloys in the Mining Industry," Paper 228, presented at Corrosion/84, National Association of Corrosion Engineers, 1984 Corrosion in Structures John E. Slater, Invetech, Inc. Introduction THE PREVENTION of metallic corrosion in structures, particularly the consideration of its effects in initial design and fabrication or later during in-service inspection and retrofit, is vital in ensuring the expected longevity of the structure. Indeed, in many cases, structures may have to last well beyond their originally anticipated lifetimes for example, the extended lives of structures in Europe that contain metal, some of which date back many hundreds of years. In considering the ramifications of corrosion and its prevention in different types of structures, it is useful to group such structures into various categories. Thus, the modern high rise whether an office building, an apartment building, a condominium structure, or a special-purpose building such as hospital poses particular problems related to the corrosion of major structural components (which may be either totally metallic or may contain metallic material) and creates the necessity for corrosion considerations in any connector assembly used to tie the curtain-wall system on the building back to the structural frame or to the backup wall system. In low-rise structures, similar concerns exist, but may be less critical when the structure is only a few stories high. Under such circumstances, the possibility of danger to people and property resulting from failure of, for example, curtain- wall tie systems may be less. Nevertheless, failure of metallic materials within structure may lead to unsightliness or to possible lack of weathertight behavior. Both may require extensive reworking of the structure to reestablish adequate building performance. Parking structures are frequently of conventionally reinforced concrete or prestressed/posttensioned construction. Where such structures are in the snow belt areas of the country or where chloride may intrude because of the proximity of marine environments, the reinforcement may be at risk from corrosion. Stadiums are another example in which either steel-frame or concrete-frame approaches can be used. In these cases, certain approaches may be needed to ensure structural integrity, particularly in view of the safety of the many thousands of people who may visit the structure and fill it to capacity. Bridges have received much attention with regard to corrosion. This has been particularly prevalent in the snow belt states, where deicing salt application has led to significant premature deterioration of decks and supporting structures. However, supporting structures have also suffered damage because of saline water intrusion, particularly in the splash zone of reinforced concrete structures. Also, the use of the weathering steels can be a problem in such structures, especially where design or construction practice does not adequately account for the particular limitations in the use of this type of steel. [...]... delineated, with particular attention paid to the different problems as they relate to different structures in which the metallic material may exist General Considerations in the Corrosion of Structures Corrosion of Steel in the Atmosphere Atmospheric corrosion is discussed at length elsewhere (see the article Corrosion of Carbon Steels” in this Volume and “Atmospheric Corrosion in Corrosion: Fundamentals,... Marine Marine Corrosion rate m/yr mils/yr 0.76 0.03 4.6 0.18 13 0.5 14. 5 0.57 14. 5 0.57 19.5 0.77 20 0.8 22.8 0.89 23 0.9 23 0.9 28 1.1 28 1.1 30 1.2 33 1.3 33 1.3 38 1.5 38 1.5 46 1.8 48 1.9 51 2.0 51 2.0 61 2.4 79 3.1 84 3.3 94 3.7 132 5.2 147 5.8 165 6.5 295 11.6 442 17.4 500 19.7 533 21.0 686 27.0 1070 42.0 Source: Ref 1 Corrosion in marine environments is a specialized subset of atmospheric corrosion. .. should resist the onslaught of the Cl- Fig 16 Corrosion and resulting masonry cracking on anchor embedded in high-bond mortar See also Fig 17 Fig 17 Corrosion and resulting masonry cracking on an anchor embedded in high-bond mortar See also Fig 16 Corrosion of Posttensioning and Prestressing Structures Unlike other cases of corrosion of steel in structures, the corrosion of posttensioning structures can... the level of the anchorages, leading to some serve corrosion This was particularly true on the gripping wedges, as illustrated in Fig 18 Fig 18 Corrosion of posttensioning anchorage Note severe corrosion at the two wedge halves Several of the anchorages were sufficiently corroded such that alternative anchorages had to be installed In others, the corrosion was slowed by the injection of water-displacing... article (see the article "Marine Corrosion" in this Volume) The dramatic increase in the corrosion rates of steel in marine locations is indicated in Table 1 Specialized environments exist in which specific pollutants are present as a function of the particular use or location of the structure Therefore, chemical plant and refinery buildings and structures may be particularly vulnerable to certain... Calculation of the Pilling-Bedworth ratio (see the article “Gaseous Corrosion Mechanisms” in Corrosion: Fundamentals, Testing, and Protection, Volume 13A of ASM Handbook) allows the magnitude of the volume expansion to be assessed, but this is typically found to be a factor of between 2 and 10, depending on the exact nature of the corrosion product The effect on high-strength prestressing steel may... can lead to accelerated corrosion Examples of details to avoid, as well as more corrosion- resistant details, are shown in Fig 4 Although some of these discrepancies can be mitigated by other corrosion protection methods, the selection of weathering steels makes adherence to good design and fabrication detailing mandatory Fig 4 Design and fabrication details to be considered in corrosion prevention (a)... therefore low corrosion rates, occurs on the zinc in the pH range of about 6 to 12.5 Figure 8 shows the influence of pH on the corrosion rate of zinc It is interesting that the pH of concrete or mortar in the noncarbonated state is typically about 12.5, which is the minimum on the pH versus corrosion rate curve for zinc This observation is supported by laboratory studies evaluating the corrosion rate... crevices formed by the flattened channel One effect of this corrosion was the interaction with low cyclic stresses imposed on the tie due to movements between the stud and the wall, leading to cracking of the tie This was particularly prevalent where corrosion had reduced the tie thickness to a fraction of its original dimension (Fig 15) Fig 15 Severe corrosion and cracking (arrows) on wall tie This problem... steel Corrosion occurs by a typical aqueous corrosion mechanism during the time that this film is present on the steel surface The thinner the film, the easier the diffusion of oxygen through the film that drives the corrosion reaction The presence of agents in the atmosphere that can dissolve in the liquid film and promote or inhibit its production by changing the dew point can markedly influence the corrosion . tool steel 414 60 131 19 145 21 152 22 Abrasion-resistant steel 307 44.5 152 22 145 21 124 18 Low-carbon steel 214 31 152 22 159 23 138 20 Stelcoloy-G steel 269 39 138 20 114 16.5 124. available in the article “Designing to Minimize Corrosion in Corrosion: Fundamentals, Testing, and Protection, Volume 13A of ASM Handbook. Fig. 6 Crevice corrosion at the intake flange of an ACI. Crook, " ;Corrosion and Wear of High Performance Alloys in the Mining Industry," Paper 228, presented at Corrosion/ 84, National Association of Corrosion Engineers, 1984 Corrosion in