Steels corrosion rate

Steel is an acceptable material of constmction for handling solutions of up to 50% NaOH below 40°C. Above 40°C the steel corrosion rate increases rapidly and iron is picked up in the solution. Materials for handling 50% NaOH are lined steel for tank cars and lined or unlined steel for tanks and piping. 

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).

Access of oxygen to steel surfaces during corrosion influences the wastage process in nonoxidizing acids. Fluid velocity can influence the amount of oxygen reaching the metal surface and, therefore, the corrosion rate. In deaerated acid solutions, steel corrosion rate is constant with fluid velocity. If dissolved oxygen is present, however, the corrosion rate is proportional to fluid velocity. 

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

Changes in steel corrosion rate for different exposure conditions and types of atmosphere are better explained based on average deposition rate of Chlorides, as can be observed on figure 5. It can be note that Chloride deposition is higher in coastal stations, as it should be expected, and it is in agreement with a higher weight lost for these stations. 

Steel corrosion rate at Campeche, Veracruz, Puerto Progreso and Puerto Morelos (flat specimens)... 

The value of steel corrosion rate ratio for Viriato and Quivican stations at six months of exposure (1154.67/108.37 = 10.65) is between Cl-DR and chloride concentration in corrosion products ratio and is higher than sulfate. There should be rapid changes in chloride concentrations due to liquid precipitations and arrival of aerosol particles. Changes in sulfate concentration should be lower than for chloride. The corrosion rate in coastal zones should depend mainly on a sum of time of wetness at different chloride and sulfate concentrations. 

Stainless steel -corrosion rates m acid [SULFAMIC ACID AND SULFAMATES] (Vol 23)... 

A disbanded mill scale can also result in a situation where the rinse water can flow and fill the gap between the mill scale and the steel substrate through the cracks/pores in the mill scale. This will result in an occluded cell situation where the chemistry of the electrolyte within the occluded cell, usually at a lower pH, will be very different from that of the bulk rinse water. This can result in the corrosion of the steel substrate. The presence of chloride will significantly increase the steel corrosion rate, as chlorides can readily migrate to the occluded region where they can lower the water pH quite readily and can increase the rate of the balancing cathodic reaction. The observation that trace levels of chloride were found within a corrosion perforation supports this discussion. 

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...

Bronze, Zinc, Aluminum, and Galvanized Steel Corrosion Rates as a Function of Space and Time over the United States... 

A pseudo steel corrosion rate was calculated by dividing steel corrosion by (0.312+0.8% ) exp(-0.702Q). This value was... 

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 ... 

The steel corrosion rate in concrete will be higher in the presence of chloride ions, which reduce the anodic polarization and enhance the conductivity of the paste [226]. Other factors are influencing also concrete resistivity, namely the low w/c ratio, low humidity and temperature decrease, all result in resistivity increase. Therefore, in dry concrete or immersed in water, its corrosion is negligible. 

By its very nature, the lASAP release rate model is sensitive to the chosen corrosion or degradation rates for the steel components and for the barrier materials. Although an extensive literature study was undertaken and advice sought from materials specialists from the contributing countries, in order to provide the best estimates, nevertheless, steel corrosion rates in the ocean can have a wide spread of values and barrier effectiveness is not well defined. 

For weathering steels corrosion product accumulated with time leading to the retardation of corrosion rate with time, whereas for mild steel corrosion rate increased with time. 

As is well known, one of the most important problems regarding steel-reinforced concrete structures is their low resistance to degradation phenomena that limits their service life and increases their maintenance cost. Under normal service conditions, the corrosion of steels embedded in concrete takes place at a very low rate due to the alkaline pH that can be found inside the concrete, but several chemical processes, due to external conditions, can modify the passive state of steel reinforcements, leading to an increase in the steel corrosion rate. For instance, the attack produced by the ingress of chloride ions into concrete causes both the breaking of the passive oxide layer of the steel surface, and a progressive acidification of the environment inside the pit. As a consequence, the corrosion rate increases inside the pit due to the low pH solution created (Garces et al., 2011). 

Location Distance from Ocesm (m) Steel Corrosion Rate 2-yr. test Mpy mm/y ... 

Tidal—The tidal zone is an environment where metals are alternately submerged in seawater and exposed to the splash/spray zone as the tide fluctuates. In the submerged condition, metals are exposed to well-aerated seawater and biofouling does occur [11,121. A continuous cover of biofouling organisms protects some metal surfaces such as steel, while the presence of biofouling on stainless steel surfaces can accelerate localized corrosion. Steel is influenced by tidal flow, where increased movement due to tidal action causes an increased steel corrosion rate [121. Curve (b) in Fig. 1 shows that steel corrosion at exposed coating defect sites is as severe in the tidal zone as it is in the splash/spray zone. 

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. 

ScuUy, J. R. and Bundy, K. J., The Use of Electrochemical Techiiiques for Measurement of Pipe Steel Corrosion Rates in Soil Environments, Corrosion 83, NACE International, Houston, TX, 1983, Paper 253. 

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. 

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. 

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

---