Carbon steel erosion-corrosion

Wear owing to corrosion and/or erosion can be particularly dangerous. For example, as carbon steel corrodes, the reduced wall thickness can eventually lead to a stmctural failure. This problem can be compounded through erosive wear of the silo wall. 

Figure 11.10 Effect of pH of distilled water on erosion-corrosion of carbon steel at 122°F (50°C) (velocity, 39 ft/s, 12 m/s). (SOURCE M. G. Fontana and N. D. Greene, Corrosion Engineering, 2d ed., 1978, p. 75. Reprinted with permission from McGraw-Hill, Inc.)...

Tower shells may be ferrous, non-ferrous, stainless alloys or clad (such as monel-clad-steel). The trays are usually light gage metal consistent with the corrosion and erosion problems of the system. The velocity action of vapors flowing through holes and slots accentuates the erosion-corrosion problems, and often a carbon steel tower will use... 

Table 1.29 tabulates most known examples of erosion corrosion problems occuring in aqueous systems. Historically, erosion corrosion first became a problem with the copper alloy (70%Cu 29%Zn l%Sn) condensers of naval shipsErosion corrosion of copper alloys has been an ongoing problem since then. The other major problem areas are (a) power plants where steels are exposed to water or water/steam mixtures in the temperature range 90°-280°C (b) the oil and gas industry where steels are exposed to various liquid, gas, and sometimes solids combinations containing carbon dioxide. 

Since the formation nature and breakdown of protective surface films depends on both material and environmental parameters such influences on erosion corrosion will be discussed together. Particular attention will be paid to the copper/seawater and carbon steel/water (steam) systems. 

Basically there are two approaches to predicting the occurrence of erosion corrosion. Practical or experience based methods typified by Keller s approach for carbon steels in wet steam. Keller developed an equation that related the erosion corrosion rate as a function of temperature, steam quality, velocity and geometric factor. In recent years this approach has... 

Morpholine is still the standard by which other amines are compared for pH control, and AMP has commonly been employed to control carbon steel boiler tube erosion-corrosion problems in European gas-cooled reactor stations. 

Seawater-based utility systems for condenser and process cooling systems in power plants exhibit serious corrosion, erosion and fouling problems. Equipment made from carbon steel and even stainless steel shows sign of degradation from galvanic effect, corrosion, erosion and microbiological induced corrosion (MIC). Corrosion... 

One report stated thickness measurement a short distance away from the rupture showed the line was a nearly full design thickness. Investigators concluded the line failure was the result of the thinning of the Schedule 120 carbon steel 90-degree elbow due to long-term erosion/corrosion. [21] Another story stated the piping was originally or nominally 0.625 inches thick, but had worn down to 0.085 inches. [27] That represents an 86-percent wall loss. 

The corrosion rate of carbon steel increases with increase in velocity until a critical velocity is reached. This behavior is different from that of the carbon steel in fresh water where the corrosion rate decreases beyond a critical velocity due to the formation of a passive him. In seawater passive films are not formed because of the presence of high concentrations of chloride. The erosion corrosion occurs after critical velocity 20 m/s is reached. The maximum corrosion rate of 1,0/mm/yr is reached at velocities up to 4 m/s. 

Problems with steam can occur in let-down valves as a result of erosion-corrosion. To prevent attack, hard facing (e.g., stellite) is commonly used when the pressure drop exceeds 150 to 200 psi (1,035 to 1,380 kPa). This limit can be raised to 500 psi (3,450 kPa) for clean, dry steam. Corrosion-erosion also occurs in wet steam. Carbon steel is unsatisfactory in wet steam when pvx, the product of the pressure (psia), velocity (ft/s), and wetness (% water) exceeds 1 x 105. Resistance to wet steam is enhanced by increasing both the metal hardness and chromium content. 

High solids (carbonates and bicarbonates) BFW will result in significant formation of carbon dioxide. The resulting carbon dioxide-laden condensate causes erosion-corrosion attack on carbon steel. Failure occurs by deep pitting, furrowing, or channeling. Corrosion inhibitors can be added to minimize this attack. 

Investigators determined that a carbon steel section of 6-inch (150 mm) line was installed in an area in which specifications required corrosion-resistant 5-percent chromium—1/2-percent molybdenum (generally called 5-chrome) alloy piping. In a process plant like a fluid coker, the materials used are a mixture of carbon steel and other steel alloys. Apparently, the welder and the maintenance crew, who previously repaired this piping some time ago, were not aware of the piping specifications. Apparently, they did not realize that if a material like carbon steel was installed in an area requiring 5-chrome alloy piping, erosion or corrosion could cause failure. 

Linings to protect floors, vessels and other equipment subjected to corrosion, erosion, abrasion and/or thermal attack from chemical environments. The most common substrates for CRM linings are carbon steel and concrete, but other structural materials such as wood and plastics may also be effectively protected. CRM linings can provide any one or all of the following protection modes ... 

In sulfuric acid production, acid brick lining of membrane coated mild steel tanks and reaction vessels is considered the most durable and versatile construction material for the sulfuric acid plant. Such linings wiil reduce the steel shell temperature and prevent erosion of the normally protective iron sulfate film that forms in stagnant, concentrated (oxidizing) sulfuric acid. Dilute (red uC ing) sulfuric acid solutions are very corrosive to carbon steel, which must be protected by impermeable (e.g., elastomeric) membranes and acid brick lining systems. Such acid brick linings often employ membranes comprising a thin film of Teflon or Kynar sandwiched between layers of asphalt mastic. 

The low pressure and mild temperatures employed, along with the absence of either a corrosive or erosive environment, allow for the use of carbon-steel construction. 

A special example is described by Fontana and Greene [7.1] The erosion corrosion rate on carbon steel in water may be higher at pH = 7-9 than at pH = 6 as well as at pH =10. The reason is assumed to be that the oxide layer at pH =7-9 consists of granular Fc304, which is less erosion resistant than the Fe(OH)2 or Fe(OH)3 dominating at the lower and higher pH, respectively. Increased content of oxidizers may also decrease or increase erosion corrosion rate depending on whether passivation is obtained or not. The temperature is another important factor. It may affect the properties of the deposits in addition to the shear stress and mass transport (see next section and Section 6.2.2). 

Figure 15.4 Mapping electrochemical material loss against mechanical erosion rates for a nonpassivating surface carbon steel (AISI1020) along with two potentially passivating surfaces of nickel aluminum bronze (NAB) one that has been thermally sprayed by high-velocity oxy-fuel deposition as a coating on carbon steel ( j and another which has been cast (A.). These results were obtained from jet impingement erosion-corrosion tests. Reprinted from Ref. [7]. Copyright (2007) with permission from Elsevier.

Copper alloys (Admiralty, copper-nickel) and austenitic stainless steels are the most commonly used materials for feedwater heater tubing based upon their resistance to general and localized corrosion, erosion-corrosion, and SCC, and adequate heat transfer performance [1,2]. Carbon and low-alloy steels are most often used for the shells of such heaters for economy and availability. 

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