Corrosion rates carbon steel

Figure 5.2 Schematic of carbon steel corrosion rate versus exposure time in a typical oxygenated cooling water. Note how the average corrosion rate decreases with time and converges to CR at t (the minimum exposure time to get reproducible results).

Table 4.9 Selected inorganic salts highly corrosive to carbon steel (Corrosion rate >50 mpy)...

Comparison of sulfur levels vs carbon steel corrosion rates.21... 

Figure 1.12 Comparison of sulfur levels vs carbon steel corrosion rates.9 Petroleum Refining Process Corrosion, Crude Fractionation Units, and Utilities 21...

The mechanism of the main cathodic reaction in CO2 corrosion has briefly been dealt with in Section 6.5. The carbonic acid reacts with steel, and a layer of reaction products, to a large extent FcCOb, is formed on the steel surface. The deposit is cathodic relative to steel, and when small defects occur in the deposit layer, pitting corrosion is developed. The conditions may be particularly corrosive in the production tubing, which carries the oil/gas up from the well. In production tubing of carbon steel, corrosion rates in excess of 10 mm/year may occur under unfavourable conditions [8.27]. Various factors contribute to the high corrosivity ... 

Carbon steels corrode in aerated seawater conditions. Their corrosion rate decreases with time as protective barrier films are formed on the carbon steel surfaces. These protective films may be a rust layer, calcareous deposits, or biofouling. The corrosion rate of carbon steels increases in high velocity seawater because the protective barrier layer is either not allowed to form or is stripped away under the flow conditions. Also, the available oxygen at the metal surface is increased in flowing seawater, which promotes a higher carbon steel corrosion rate. 

RG. 5—The relationship of the organic nitrogen and organic sulfur content of crude oil on carbon steel corrosion rate in crude oil/brine mixtures [73. (4% NaCI brine at. 2 mPa CO2 pressure and 85 C.)... 

FIG. 8—Carbon steel corrosion rate on a iogarithmic scale for crude oil/brine mixtures using different crude oils with the same brine composition (4 % NaCI solution) [13. ... 

FIG. 10—The change in carbon steel corrosion rate of steel in crude oil/produced water mixtures with Increasing produced water content showing the three general types of behavior observed. 

FIG. 1—Relative carbon steel corrosion rate versus elapsed time. 

From this study, it can be seen that raising the chloride load has a mnch stronger effect on painted zinc-coated substrates than on painted carbon-steel snbstrates. It is known that for bare metals, the zinc corrosion rate is more directly dependent than the carbon steel corrosion rate on the amonnt of pollutant (NaCl in this case). This relationship may be the cause of the results in the table above. In addition, higher salt levels leave a heavier hygroscopic residue on the samples (see Section 7.2.3) this may have caused a thicker moisture film at RH levels above 76%. 

Third, the low volatility and low Br reserve required has tended to reduce actual rates of both copper and carbon steel corrosion. 

The passive film of galvanized rebars is stable even in mildly acidic environment, so that the zinc coating remains passive even when the concrete is carbonated. The corrosion rate of galvanized steel in carbonated concrete is approximately 0.5-0.8 pm/y, therefore a typical 80 pm galvanized coating would be expected to last over 100 y. [44]. The corrosion rate of galvanized bars remains negligible in carbonated concrete even if a low content of chloride is present. 

By bacterial manipulation, what is meant is that certain bacteria are used to slow down corrosion. For example, it has been reported " that carbon steel corrosion in presence of the biofihn of aerobic bacterium Pseudomonas fragi or the facultative anaerobe Escherichia coli had been slowed down by 2-fold to 10-fold. Another example is a biofilm-producing baclerinm, identified as Bacillus sp., that was able to reduce corrosion rates of mild steel by establishment of antimicrobial agent-producing biofllm, which inhibited the activity of SRB. 

FIGURE 9.5 Corrosion rate as a function of CO2 partial pressure at four different HjS levels at38°C for API grade X52 tube. (From C. de Waard and U. Lotz, Prediction of CO2 corrosion of carbon steel. Corrosion/93, paper 69. NACE, Houston, TX, 1993. With permission.)... 

Dugstad, A., Lunde, L., and Videm, K., "Influence of Alloying Elements upon the CO2 Corrosion Rate of Low Alloyed Carbon Steels," CORROSION/91, NACE Annual Conference 1991, Paper No. 473. 

General guidelines for acceptable uniform corrosion de-p>end upK>n the coupx>n met Jlurgy. Low-carbon steel (mild steel) corrosion rates less than 0.13 mm/y (5 mpy) are considered good, rates between 0.13 to 0.25 mm/y (5 to 10 mpy) are fair, and rates greater than 0.25 mm/y (10 mpy) are pKK>r. Copp>er-base alloys, such as admiralty and 90 10 copper nickel, should have rates under 0.013 mm/y (0.5 mpy). Above this value is considered excessive. General classification of corrosion rates is shown in Table 4. 

Zinc is more resistant to atmospheric corrosion than carbon steel. The rate of corrosion of zinc is influenced primarily by the time of wetness and the presence of pollution in the air, specifically CO2, SO, and Cl. ... 

Carbon steel corrosion by COj is directly dependent upon temperature. At temperatures below 60 °C scale provides little corrosion protection. In the temperature range of 60 to 100 °C, iron carbonate will form. The scale may result in lower than predicted corrosion rates, but severe pitting can (and usually does) occur. 

M. Foss, E. Gulbrandsen, J. Sjoblom 2008. Alteration of wettability of corroding carbon steel surface by carbon dioxide corrosion inhibitors - Effect on carbon dioxide corrosion rate and contact angle. Corrosion 64 (12), 905-919. 

The corrosion rate of steel in carbonic acid is faster than in hydrochloric acid Correlations are available to predict the rate of steel corrosion for different partial pressures of CO2 and different temperatures. At high temperatures the iron carbonate forms a film of protective scale on the steel s surface, but this is easily washed away at lower temperatures (again a corrosion nomogram is available to predict the impact of the scale on the corrosion rate at various CO2 partial pressures and temperatures). 

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