Steel pipelines will be corroded and damaged by the environment in the air or buried underground. In order to prevent corrosion and damage of steel pipelines, anti-corrosion layers and cathodic protection methods are usually used to protect the pipelines. The function of the external anti-corrosion layer is to isolate and insulate the surface of the steel pipe from the surrounding environment to achieve the purpose of inhibiting corrosion. Cathodic protection works by reducing the corrosion potential. That is, when a buried steel pipe is exposed and corroded, the corrosion electrons are first provided by the cathodic protection current instead of the iron in the steel pipe. In this way, the purpose of electrochemical protection is achieved. Regarding the role of external anti-corrosion layer protection and cathodic protection, most experts believe that external anti-corrosion layer protection is the main one, accounting for 99%, and cathodic protection is auxiliary.
When the outer anti-corrosion layer of buried pipelines is full of holes, cathodic protection will not be able to play its role and may even have negative effects, such as cathodic stripping.
Introduction to several commonly used pipeline anti-corrosion methods in oil fields
Petroleum asphalt anti-corrosion layer:
The petroleum asphalt anti-corrosion layer is an external anti-corrosion layer for buried pipelines made of petroleum asphalt-impregnated glass fiber cloth wrapped around it. It is the most commonly used pipeline covering material. Its advantages are wide sources of raw materials, mature technology and low price. Its disadvantage is water absorption. It is large, resistant to temperature differences, easy to age, has poor resistance to bacteria, and is easily damaged by the roots of reeds and other plants.
Fusion bonded epoxy powder anti-corrosion layer
Fused epoxy powder (FBE) is a one-component coating composed of epoxy resin, curing agent, filler and pigment. The FBE anti-corrosion layer has strong adhesion to the steel pipe, superior corrosion resistance and good mechanical properties. The disadvantages are high water absorption, limited impact resistance, high rust removal quality requirements, and high cost.
Epoxy coal pitch anti-corrosion layer:
Epoxy coal tar pitch coating is a two-component curing coating composed of epoxy resin, coal tar pitch, curing agent, filler, etc. It has been used in my country since the 1970s, and the operating temperature is - 20 ~ 100 ℃. Its performance is between coal tar enamel, sintered epoxy powder and polyethylene, and it is widely used in petroleum and water supply projects in my country. Due to environmental protection requirements, its application has been inhibited to a certain extent in recent years.
3PE anti-corrosion layer
The 3PE anti-corrosion layer, first developed and launched by Germany in the 1980s, combines the anti-corrosion properties of sintered epoxy powder with the mechanical scratch protection properties of polyethylene to make its performance more complete. Its composition is: epoxy Powder coating primer + copolymer adhesive layer + polyethylene outer protective layer.
The advantages of this anti-corrosion layer are high insulation resistance, strong adhesion, good mechanical properties such as impact resistance and wear resistance, resistance to plant root penetration, and good chemical stability. Therefore, it is suitable for pipelines in various environments with harsh laying and construction conditions. However, the price of this anti-corrosion layer is high, and it has high requirements on the surface treatment and coating process of steel pipes. The patching of the anti-corrosion layer is difficult, and the construction process needs to be strictly controlled to ensure its quality.
Polyethylene adhesive tape anti-corrosion layer
The main advantages of polyethylene adhesive tape are high insulation resistance, good resistance to stray current and easy construction. The disadvantage is that it has poor soil stress resistance. This anti-corrosion layer is suitable for pipeline repair and pipe fitting anti-corrosion.
