Water with a high alkalinity is more likely to be scale-forming even at a relatively low pH. In contrast, low alkalinity waters lack the buffering capacity to deal with acids, so they can easily become acidic and corrosive. Secondary Water Characteristics. Other chemicals and compounds found in water also influence the corrosion process. The most common of these are oxygen, carbon dioxide, and dissolved solids. Oxygen reacts with hydrogen gas at the cathode, causing depolarization and speeding up the corrosion.
As a result, water with a high D. Other oxidizing agents can perform the same function, although they are less common. Nitrates and chlorine are two other oxidizing agents found in water. Carbon dioxide in water also tends to cause corrosion. The carbon dioxide gas can combine with water to form carbonic acid, which lowers the pH of the water. As mentioned in the last section, a low pH promotes corrosion. Dissolved solids are typically present in water as ions.
These ions increase the electrical conductivity of the water, making the electrolyte more effective. Thus, they will increase the rate of corrosion. Physical Water Characteristics In addition to the chemical properties of water, physical characteristics will influence corrosion. The most important of these physical characteristics are temperature and velocity of flow.
Temperature speeds up the rate of corrosion just as it does most other reactions. However, the effect of temperature on corrosion can be more complex. A high water temperature reduces the solubility of calcium carbonate in water, which promotes scale formation and slows corrosion. Temperature also alters the form of corrosion. Pits and tubercles tend to form in cold water while hot water promotes uniform corrosion. Uniform corrosion spreading across the entire surface of a pipe is far less problematic than tuberculation, so high temperatures can actually seem to slow the corrosive process.
Acidic soils include highly organic soils, and soils where soluble salts are stripped out due to heavy rainfall. Soil pH can be determined by either colorimetic analysis or electometric analysis. Colorimetic measurement is simple and easily performed in the field. A sample of soil is mixed with water and a chemical, and the pH is determined by comparing the resulting color change with a color chart based on pH values. However, determination can sometimes be difficult because mixing the soil with water can turn the solution turbid resulting in interference with determination of the pH.
Electrometic analysis equipment can be used both in the laboratory as well as in the field. In the lab, the soil is normally air-dried, mixed with water, and then tested. The lab results generally correspond well with field measurements, except for some poorly aerated soils that have high concentrations of soluble sulfur in which case the lab results show lower pH values.
Also realize that the pH value of soil can change over time with variations in climate and other factors. So what does pH have to do with soil corrosion? That depends on the type of buried metal. When the pH is between about 4 and 10, soil corrosion is independent of pH. When the pH is greater than 10, the metal becomes passive and corrosion rates decrease with increasing pH. For example, placing reinforcing steel in concrete sound concrete pH is normally around 11 provides good protection of the steel.
Effects of high pH on corrosion. Low pH can cause so many adverse effects but what are all the possible effects of high pH? This question arises because of limits used for pH. There is always a limit to the upper side too. For example, pH should remain within 5.
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