Common surface treatment processes for oil casing pipe

Surface treatment of oil casing pipe is a key link to improve its corrosion resistance, wear resistance and service life. The following are the commonly used treatment processes in the industry:

Coating treatment (most mainstream process):

1. Galvanizing (Zn Coating)

Features: Through hot-dip galvanizing or electrogalvanizing process, a zinc protective layer is formed, and the sacrificial anode protects the steel pipe matrix.
Advantages: Low cost, mature process, suitable for general corrosive environment (such as fresh water, weak alkaline environment).

Limitations: Easy to fail at high temperature (>60℃) or high chloride ion environment.

2. Zinc-aluminum alloy coating (Zn-Al Coating)

Common types: Galvalume (55%Al-Zn), Galfan (5%Al-Zn).
Advantages: Corrosion resistance is 2-5 times higher than that of pure zinc coating, and high temperature resistance is better (up to 300℃).

3. Epoxy coating (FBE/Fusion Bonded Epoxy)

Process: Electrostatic spraying followed by high temperature curing to form a dense polymer film.
Application: Mainly used for casing outer wall corrosion protection, especially suitable for offshore platforms and high saline-alkali formations.

FBE coating is widely used in industry due to its excellent adhesion, impact resistance and cathodic stripping resistance. The process involves heating the pipe surface and applying epoxy powder, which melts and fuses to form a protective layer. FBE coating effectively prevents corrosion caused by water, soil and other corrosive agents.

Chemical conversion treatment:

1. Phosphating
Function: Generate a phosphate film layer to improve surface adhesion (commonly used for pretreatment before plating or painting).

2. Passivation
Applicable materials: stainless steel casing (such as 13Cr, Super 13Cr).

Principle: Remove surface free iron by pickling to form a chromium oxide passivation film.

Pickling: Chemical or electrolytic methods are used to remove scale, rust and old coatings on the surface of steel. Chemical pickling can effectively remove these impurities, and sometimes it is even used as a supplementary treatment after sandblasting. Although chemical cleaning can improve the cleanliness and roughness of the surface, the anchor pattern it produces is shallow and may cause a certain degree of pollution to the environment.

Mechanical strengthening treatment:

1. Shot Peening
Purpose: By impacting the surface with high-speed projectiles, a compressive stress layer is introduced to improve fatigue resistance.

Use a high-power motor to drive the spray (blasting) blade to rotate at high speed, so that abrasives such as steel sand, steel shot, wire segments and minerals are strongly sprayed (blasted) on the surface of the steel pipe under strong centrifugal force. This process can not only completely remove rust, oxides and dirt, but also achieve the required uniform roughness of the steel pipe through the violent impact and friction of the abrasive. Shot blasting (sand) rust removal is suitable for the treatment of the inner surface of the pipe, while shot blasting (sand) rust removal is more used for the outer surface of the pipe.

2. Special treatment of threads
Copper plating/tin plating: improve thread air tightness and prevent sticking (such as VAM TOP, FOX and other high-end buckle types).
PTFE spraying: polytetrafluoroethylene coating to reduce friction coefficient.

Special treatment for special environments:

1. Nickel-based alloy cladding
Application: used in extreme corrosive environments (such as high-temperature and high-pressure wells containing H₂S/CO₂).

2. Ceramic coating
Scenario: shale gas well fracturing section casing, resisting high-speed sand erosion.

Trends in the oil pipeline surface treatment industry:

Currently, it is more inclined to composite treatment (such as "zinc-aluminum coating + FBE" double protection) and develop intelligent coatings (such as self-healing coatings). For deep wells and ultra-deep wells, the surface treatment cost may account for 15%-30% of the total casing cost, but it can significantly reduce the subsequent maintenance costs.

Read more: Types of drilling casing pipe or Anti-corrosion measures for well casing pipe