316 stainless steel pipe is widely used for its excellent corrosion resistance, high strength, and good processability. However, in some extreme operating conditions or where the purity of the medium is extremely high, the inherent properties of 316 stainless steel alone may not meet the requirements. In such cases, coating the inner wall of 316 stainless steel pipe is necessary to enhance its performance and expand its application range.

Surface Pretreatment
Before coating, surface pretreatment of the inner wall of 316 stainless steel pipe is crucial. First, mechanical cleaning, such as using a dedicated pipe cleaning brush or high-pressure water jet, removes impurities such as oil, rust, and welding slag from the inner wall. Chemical cleaning, using an appropriate acid or alkaline solution, further removes oxide films and residual impurities from the metal surface. Finally, surface roughening treatment, such as sandblasting or electrolytic etching, increases the surface roughness and improves adhesion between the coating and the substrate.

Coating
A variety of coating methods are available, depending on the coating material and application requirements. PTFE coatings are often applied by spraying. PTFE powder is mixed with a binder and evenly applied to the pipe's interior using a high-pressure spray gun. The coating is then cured by high-temperature sintering. Epoxy resin coatings can be applied by brush, roller, or high-pressure airless spray, creating a uniform coating on the pipe's interior. The coating is then cured at a specific temperature. Ceramic coatings are often applied using thermal spraying techniques, such as plasma spraying and supersonic flame spraying. Ceramic powder is heated to a molten or semi-molten state and then sprayed onto the pipe's interior at high speed, forming a dense ceramic coating.

Post-Processing
After coating, post-processing is required. To further enhance coating performance, heat treatment, such as high-temperature baking, can be performed to stabilize the coating's molecular structure and enhance its hardness and wear resistance. Coating quality is also tested. Visual inspection, coating thickness gauges, and adhesion tests are used to check whether the coating meets requirements for thickness, uniformity, and adhesion, ensuring the coating meets the desired standards.

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