The process of applying a protective coating to steel pipes to make them corrosion-resistant. Different anti-corrosion processes are selected depending on the usage environment (buried, overhead, subsea, transported medium).
The process of applying a protective coating to steel pipes to make them corrosion-resistant. Different anti-corrosion processes are selected depending on the usage environment (buried, overhead, subsea, transported medium).
A. External Anti-corrosion Processing Methods
1. Three-layer polyethylene anti-corrosion (3PE)
Currently the absolute mainstream and highest standard for external anti-corrosion of buried pipelines.
Processing flow: Steel pipe surface treatment (sandblasting) → Heating → Epoxy powder coating (bottom layer, providing adhesion and chemical corrosion protection) → Adhesive layer extrusion winding (middle layer, bonding) → Polyethylene layer extrusion winding (outermost layer, providing mechanical protection and isolation).
Features: Combines the adhesiveness and corrosion resistance of epoxy with the mechanical properties of polyethylene, resulting in an extremely long corrosion resistance life (up to 50 years or more).
2. Fusion-bonded epoxy powder anti-corrosion (FBE)
Processing flow: Steel pipe preheating → Electrostatic spraying of epoxy powder → Powder melts, flows, and cures on the pipe wall to form a continuous coating.
Features: Extremely strong adhesion, good chemical corrosion resistance, thin coating, but weak resistance to mechanical impact and scratches. Commonly used for pipelines operating at high temperatures or as a base layer for 3PE.
3. Double-layer epoxy anti-corrosion (2FBE)
Processing: A thicker modified epoxy coating is applied over the FBE coating.
Features: More resistant to mechanical damage than single-layer FBE, commonly used in harsh environments such as directional drilling crossings and rocky areas.
4. Epoxy coal tar pitch anti-corrosion
Processing: After rust removal from the steel pipe, epoxy coal tar pitch-impregnated fiberglass cloth is brushed or wrapped around it, in multiple layers (often "three layers of cloth and five layers of oil" or more).
Features: Lower cost, simpler construction, but poorer environmental performance and lower performance than 3PE. Currently mainly used for small-diameter pipelines or repair joints.
5. Polyurea/polyurethane coating
Processing: Using specialized spraying equipment, the two-component material is sprayed onto the pipe wall at high speed, allowing for rapid reaction and curing.
Features: The coating is tough, wear-resistant, and has good weather resistance. It is commonly used in overhead pipelines, crossing sections, joints, and marine environments.
6. Galvanizing
Processing flow: Hot-dip galvanizing or electro-galvanizing.
Features: Provides cathodic protection (sacrificial anode), but the zinc layer is relatively thin. It is mostly used for low-pressure, exposed pipelines, such as fire pipes and guardrails.
B. Internal Anti-corrosion Processing Methods
1. Liquid Epoxy Coating Internal Anti-corrosion
Processing flow: Sandblasting the inner wall of the steel pipe to remove rust → Centrifugal spraying or spraying with a spray rod inserted into the pipe → Curing.
Features: Smooth and drag-reducing, preventing corrosion and scaling on the inner wall of the pipeline. It is the most commonly used internal anti-corrosion method for transporting water, oil, gas, and chemical media.
2. Cement Mortar Lining
Processing flow: Cement mortar is evenly applied to the inner wall of the steel pipe using a centrifuge.
Features: Mainly used for water pipelines. It is inexpensive, can maintain water quality for a long time, and prevents scaling, but it is not resistant to acid and high-speed fluid erosion. 3. Plastic/Epoxy Resin Lining
Processing Flow: A pre-made plastic pipe (such as HDPE) is inserted into the steel pipe, or coated using a rotary sintering process.
Features: Used for conveying highly corrosive media, such as slurries and acidic wastewater.
For a standard buried 3PE anti-corrosion steel pipe, the complete processing sequence is typically:
Steel pipe inspection → Surface pretreatment (sandblasting to Sa2.5 grade) → Preheating → Epoxy powder coating → Adhesive/polyethylene side winding → Cooling → EDM pinhole inspection → Coating thickness inspection → Pipe end treatment (reserving welding sections) → Marking and finished product protection → Shipment.
Shengtian Group supplies various
anti-corrosion steel pipes. If you have any needs in this area, please feel free to email us: stcompany@stpipefitting.cn
