Corrosion is a natural process, in which a metal gradually is destructed by a chemical or electrochemical process while contacted with its environment. Typical sources of corrosion are pH, CO2, H2S, chlorides, oxygen and bacteria. Oil or gas are called “sour” when the concentration of hydrosulfides, H2S, is higher than usually. Oxygen is extremely problematic on injection wells, EOR. Already very low concentrations cause high corrosion rates. In this case oxygen scavangers are used.
Bacteria can grow inside pipes and tanks under anaerobic conditions, which generates high concentrations of H2S. Pitting is a result of this and can get severe. Bacteria build-up mostly happens in low velocity applications. Other contributing factors for corrosion are temperature, abrasion, pressure, velocity and the presence of solids.
We know the following common types of corrosion:
1. Local corrosion: pitting, crevice corrosion, filiform corrosion
2. Galvanic corrosion
3. General attack corrosion
4. Flow-assisted corrosion, FAC
5. Intergranular corrosion
6. De-alloying
7. Environmental cracking: stress, fatigue, H2-induced, liquid metal embrittlement
8. Fretting corrosion
9. High temperature corrosion
For controlling corrosion the following measures are important to regard:
● Be specific in selecting the right material. Metallurgic specialists define which metals are best to use.
● Also coating and painting are relevant topics to choose well.
● Adjusting production to increase or decrease the velocity in a pipe.
● In case particles are present in the fluid, a decrease may be better for the lifetime of instruments and pipes.
● Controlling the pH, reducing the chloride quantity, eliminating oxygen and bacteria and reducing the rate of metal oxidation with chemical injections.
● Effective and best composition of the chemicals to regulate the pressure in the pipeline or vessel where the fluid needs to go in.
article source: https://www.control-lines.com/news/infrastructure-protection-injecting-chemicals-to-inhibit-corrosion/
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