1. Casing corrosion problem
With the rapid development and expansion of the petroleum industry, the obvious corrosion of oil and gas well casings, buried pipelines, storage tank floors, especially oil casings in oil fields has had a significant impact on the production, manufacturing, research, and development, supervision and environment of the oil fields. There is corrosion on both the inner and outer walls of the oil casing, among which internal corrosion is more obvious.In addition, in well sections where the well deviation changes greatly, the mechanical damage caused by the oil pipeline to the casing during operation accelerates the corrosion and holes of the casing; existing welding defects, gaps in the threads, etc. can easily cause the surface layer of the steel pipe to The difference in electrochemical properties also causes obvious corrosion damage. To solve the internal corrosion problem of oil casing, we usually add bactericides and corrosion inhibitors in the annular space of oil and gas wells, adjust the pH value, use closed oxygen isolation technology, and select low-strength oil casing in sulfur-containing oil fields.
2. Cathodic protection of OCTG casing
(1)What is cathodic protection?
Cathodic protection technology is a type of electrochemical protection technology. Its principle is to apply an external current to the surface of the corroded metal structure, and the protected structure becomes the cathode, thereby suppressing the electron migration that occurs in metal corrosion and avoiding or weakening the corrosion process. occur.(2) The significance of cathodic protection steel casing
To deal with the corrosion problem on the surface of the oil casing, cathodic protection technology should be used. At present, this has been recognized by people in the anti-corrosion industry at home and abroad. To avoid soil corrosion in underground steel buildings, cathodic protection is a more economical, scientific, reasonable, and very efficient technical measure. Cathodic protection is a safe, reliable, mature, and complete anti-corrosion technology application. It has the characteristics of strong maintenance capabilities, simple engineering construction, and low project investment. This technology is increasingly used in oil and gas, petrochemical, municipal engineering, and other sectors. The application of cathodic protection technology can not only prevent corrosion of newly built oil casings but is also very efficient for rebuilding old oil casings. It can extend the service life and reduce the number of replacements, and the economic benefits are undeniable.(3) Principle of cathodic protection metal bushing
The principle of cathodic protection is to add a large amount of electrons to the metal, so that the entire protected metal is in a state of excess electrons, so that all points on the metal surface reach the same negative potential, and the metal atoms are not easy to lose electrons and become ions and dissolve into the solution. There are two ways to achieve this purpose, namely, sacrificial anode cathodic protection and impressed current cathodic protection.(4) Method of cathodic protection casing
There are two ways to achieve corrosion protection of bushings, namely sacrificial anode cathodic protection and impressed current cathodic protection.①Sacrificial anode cathodic protection
It connects a metal with a more negative potential to the protected metal and puts it in the same electrolyte so that the electrons on the metal are transferred to the protected metal so that the entire protected metal is at the same potential, which is more negative. This method is simple and easy to implement, does not require an external power supply, and rarely causes corrosion interference. It is widely used to protect small (current is generally less than 1 amp) or metal structures in low soil resistivity environments (soil resistivity is less than 100 ohm.m)—for example, urban pipe networks, small storage tanks, etc.
②Impressed current cathodic protection
This is done by adding an external DC power supply and an auxiliary anode to force the current to flow from the soil to the protected metal, lowering the potential of the protected metal structure to the surrounding environment. This method is mainly used to protect large metal structures or metal structures in soil with high soil resistivity.Related Reading:
