Corrosion rate of steel

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). 

Hence, copper heat exchanger tubes handling acetic acid can he more seriously corroded at low temperatures than at high temperatures. Sulfuric acid at room temperature is handled routinely in carbon steel drums and tanks when water concentration is low, but it becomes extremely corrosive as water concentration increases. As ferric-ion concentration increases during acid cleaning of industrial systems, the corrosion rate of steel increases rapidly. 

Table 2.5. Corrosion Rates of Steel and Zinc Panels Exposed for Two Years (11]...

Tables 2.3 through 2.5 give general corrosion-resistance ratings of different materials. Table 2.3 lists various metals and Table 2.4 gives ratings for various nonmetals. Table 2.5 gives typical corrosion rates of steel and zinc panels exposed to the atmosphere in various locations about the U.S. Figure 2.1 also illustrates relative corrosion rates of steel and zinc in major areas of the world.

Figure 3.3. Effect of temperature on corrosion rates of steels in crude oil containing sulfur [121.

Corrosion rates of steel and zinc panels exposed for two years. .. 35... 

It is also of interest to note that Wranglen considers that the decrease in the corrosion rate of steel in the atmosphere and the pitting rate in acid and neutral solution brought about by small alloying additions of copper is due to the formation of CU2S, which reduces the activity of the HS and Scions to a very low value so that they do not catalyse anodic dissolution, and a similar mechanism was put forward by Fyfe etal. to explain the corrosion resistance of copper-containing steels when exposed to industrial atmospheres. 

Despite these results it should not be assumed that corrosion rates of steel will necessarily be low in all comparatively non-polluted desert environments. In regions such as the Arabian Gulf, considerable variations in corrosion rates may occur between inland and coastal sites. This arises not only... 

The corrosion curves in Fig. 3.4 were obtained some years ago. Corrosion is markedly influenced by the pattern of pollution, which is changing in the United Kingdom, and consequently the long-term corrosion rates may change. There is some evidence based on more recent tests to indicate that in many industrial environments the corrosion rate of steel over periods of 15 years will drop to a greater extent than is shown in Fig. 3.4. 

Table 3.42 Corrosion rate of steels and irons in the atmosphere (g m d )...

Most of the published evidence suggests that marine fouling cover— particularly where it is continuous and well established — reduces corrosion rates of steels . Indeed, 35%o seawater is by no means the most corrosive of saline environments towards steel. Brackish water, as found in estuarine or certain other coastal areas, is considerably more aggressive towards steel, and careful design measures should be taken to ensure that effective corrosion control is achieved in such circumstances. 

The majority of the applications of anodic protection involve the manufacture, storage and transport of sulphuric acid, more of which is produced world-wide than any other chemical. Oleum is 100% sulphuric acid containing additional dissolved sulphur trioxide. The corrosion rate of steel in 77-100% sulphuric acid is 500-1 000 my" at 24°C and up to 5 000 my at 100°C which indicates the necessity for additional protection. 

Oxygen infiltration coupled with (steam volatile) carbon dioxide produces enhanced condensate line corrosion. The corrosion rate of steel in the system is particularly high when both gases are present. 

In another study, polyaspartic acid was examined as a corrosion inhibitor for steel as a function of pH and temperature [1629]. At low to neutral pH values, polyaspartic acid increases the corrosion rate of steel. At pH values above 10, polyaspartic acid is a reasonably robust corrosion inhibitor. 

The lower values of Chloride deposition are reported for the storehouses, where coincidently, there are reported the lower weight losses. Under heat trap conditions there is a given increase in Chloride deposition, that is why corrosion rate of steel is higher than in storehouses. 

Changes of corrosion rate of steel as function of distance to the shoreline are lower respecting Veracruz. It is in perfect agreement with the influence of Chloride deposition. In the case of Puerto Morelos and Puerto Progreso it is also reported a significantly higher corrosion rate respecting Campeche. 

It is veiy well known that in tropical climate there are two main seasons, rainy season and dry season. Under this conditions, the acceleration caused by chlorides should be higher in the dry season (winter period) and lower in the rainy season. As an example, on Table VII presents statistical parameters calculated for corrosion rate of steel at Viriato coastal stations for periods of six months corresponding to the wet season (may to October) and dry season (november to april). All steel samples were exposed for a six months period corresponding, starting on may or on november. Data correspond to the period may/1987 to November/1991. 

Table VII. Average corrosion rate of steel, standard deviation, average Chloride deposition rate, standard deviation and aerage TOW-... 

The corrosion rate of steel increases proportionally with temperature up to about 180°F (80°C) in open air systems. At higher temperatures, oxygen is driven from the system and corrosion rates decline significantly. The effect of dissolved oxygen on the rate of mild steel corrosion is shown in FIGURE 6-13. 

NOTE The general corrosion rate of steel in an untreated cooling water system is typically 35 to 40 mpy, so a good chemical treatment program can be expected to reduce this general rate of corrosion by some 90 to 95%. 

The overall corrosion rates obtained for periods 1-40 yr range from 0.02 to 0.37 mm/yr with an average value of 1 mm/yr. The corrosion rate of steel was found to decrease with time as is evident from the data obtained by Southwell and Alexander.10... 

Some data on the corrosion rates of steel coated with zinc in soils are given in Table 4.80. The factors identified to cause corrosion in soils are (i) poorly aerated soils (ii) high concentrations of chlorides and sulfates causing pitting (iii) mud, clay and peat are more corrosive than sand. 

Simulated laboratory corrosion rates of steel/Al in solutions of interest both with added copper and without copper ... 

The corrosion resistance of steel can be greatly increased by alloying with chromium to form the stainless steels. Figure 12 shows the effect of increasing chromium content on the corrosion rate of steel. At 12-14% Cr there is a dramatic decrease in corrosion rate. The corrosion resistance is due to the formation of a thin adherent layer of chromium oxide on the steel surface [23]. The steel will remain stainless provided the oxide layer remains intact or can be rapidly repaired, i.e. the steel is exposed to oxidising conditions. The precipitation of chromium carbide at grain boundaries will cause disruption of this oxide film (See Sect. 3.2.5) and hence localised corrosion. Precipitation of chromium carbide can be reduced by alloying with elements which form carbides more readily than chromium, e.g. titanium, niobium, and tantalum. 

Fig. 12. Effect of alloying with chromium on the corrosion rate of steel. References pp. 277-279...

Corrosion rates of steel in a crude unit secondary tower overhead. 19... 

Corrosion rate of steel vs temperature of atmospheric tower sour condensate water. 19... 

Figure 1.7 Corrosion rate of steel vs temperature Figure 1.8 Effect of pH on corrosion rate of iron of atmospheric tower sour condensate in solution of the same H2S activity.7...

The effect ofpH is specific to the particular metal or alloy involved as described in chapter 10. Steel is a common material of construction and Fig. 10.4 describes the corrosion rate of steel in relation to pH. Minimum corrosion occurs at a pH of about 12. At higher pH the corrosion rate increases and soluble reaction products are formed. In the pH range 6.5 - 9.5 the corrosion rate is almost constant. The rate increases for lowvalues (< 4.0). 

For example, the corrosion rate of steel in 0.01 % Na2Cr207 is <0.0001-in. penetration per year (i.p.y.), but on addition of NaCl to make a 3.5% solution, the rate increases to 0.0017 i.p.y., which is still a low rate. In absence of dichromate, the rate is 0.024 i.p.y. Halide ions catalyze reduction of dichromates probably by introducing imperfections in the adsorbed film (through competitive adsorption), at which areas metal ions not only enter solution but also HjO+ can discharge and hydrogen atoms can adsorb. It is probably the adsorbed hydrogen atoms that reduce adsorbed chromate, or dichromate. The situation is similar to that described by Langmuir... 

The authors have studied the effect of polymer powders and films on corrosion rate of steels and their physical-chemical properties in aqua solutions of electrolytes. The experimental method was as follows. 

Fig. 2.42. The range of compositions of PE + mineral oilMO + oil-soluble Cl film materials promoting the required deformation, strength and anticorrosion characteristics. Isolines (1) breaking stress at tension Of, = 10 MPa (2) relative elongation at rupture e = 500% (3) corrosion rate of steel beneath the film in 1 N aqua solution of Na2S04, i = 0.1 mg/(m -h). Arrows indicate desired alterations of film properties...

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