Enhancing Stainless Steel Fittings' Corrosion Resistance: Coating Techniques

Improving the corrosion resistance of stainless steel pipe products is a multifaceted process involving material selection, surface treatment, alloy addition, coating technology, design, manufacturing and maintenance.

I. Measures

(1) Balance between corrosion resistance and cost: 

Select the appropriate grade according to temperature, pressure, chemical medium, and application environment. 316 stainless steel has better corrosion resistance than 304 stainless steel due to its higher molybdenum content, and is particularly suitable for marine environments and chemical processing industries.

(2) Material machinability: Select materials that are easy to process and weld to reduce difficulties in the manufacturing process.

2. Surface treatment technology

(1) Pickling treatment: remove impurities such as oxide scale, welding slag and rust on the surface of stainless steel. After pickling and polishing, it should be thoroughly cleaned and dried to prevent residues from affecting corrosion resistance.

(2) Electrolytic polishing: a dense nickel film and chromium film are formed on the surface of stainless steel.

(3) Passivation treatment: a dense protective film is formed.

3. Adding alloying elements

(1) Select appropriate alloying elements such as chromium, nickel, molybdenum, etc., and accurately control the amount of alloying elements added according to the required corrosion resistance.

(2) Evenly distribute during the smelting process. Heat treatment may be required after adding alloying elements to optimize the microstructure and properties of the material.

4. Coating technology

(1) Surface pretreatment: Ensure that the surface before coating is clean, dry and free of oil.

(2) Select appropriate coating material and thickness: Select appropriate coating material according to the use environment, such as epoxy resin, polyurethane, etc., and apply the coating evenly by spraying, dipping or brushing.

(3) Curing conditions: Ensure that the coating cures at the appropriate temperature and time to form a solid protective layer.

5. Reasonable design and manufacturing

(1) Stress concentration: Avoid stress concentration areas during design, as these areas are prone to corrosion.

(2) Welding quality: Ensure welding quality, as welding areas are often weak links for corrosion.

(3) Surface roughness: Control surface roughness, as rough surfaces are prone to accumulation of corrosive substances.

II. Coating

1. Physical vapor deposition (PVD):

It usually used for tools and parts that require high hardness, wear resistance and corrosion resistance, such as cutting tools, molds, medical devices, etc.

(1) PVD coating has excellent wear resistance, corrosion resistance and heat resistance.

(2) It can prepare film layers with wear resistance, corrosion resistance, decorative, conductive, insulating and other properties.

(3) The processing temperature can be controlled below 500℃.

2. Chemical vapor deposition (CVD):

It mainly used for surface treatment of cemented carbide indexable cutting tools, and has important applications in aerospace, automobile manufacturing, mechanical engineering and other fields.

3. Electroplating:

It used to improve the wear resistance and decorative properties of stainless steel, such as kitchen utensils, bathroom accessories, etc., and is widely used in electronics, optics, machinery, construction, light industry, metallurgy, materials and other fields.

The electroplating layer can be metal or alloy, such as chromium, nickel, etc., to enhance its wear resistance and decorative properties.

4. Mirror treatment:

It widely used in architectural decoration, kitchenware, elevators and other fields.

(1) Through physical or chemical polishing, the stainless steel surface is polished to a mirror-like smoothness.

(2) Chemical polishing uses chemical solutions to react with the stainless steel surface to form a smooth and dense oxide film.

5. Sandblasting: burr removal and surface beautification of machined parts to improve the mechanical properties of parts.

(1) Using the power generated by air compression, metal particles or abrasives are sprayed at high speed onto the surface of stainless steel, changing its surface morphology through impact and grinding.

(2) Forming uniform silk texture, frosted texture or granular texture, giving stainless steel a unique frosted texture.

(3) Sandblasting is the most thorough, versatile, rapid and efficient cleaning method.

6. Chemical treatment: pickling passivation, electroplating, chemical solution, chemical oxidation.

7. Surface coloring: chemical oxidation coloring, electrochemical oxidation coloring, ion deposition oxide coloring and high temperature oxidation coloring, etc.

8. Surface brushing: A series of parallel lines are created on the surface of stainless steel by mechanical methods, forming straight lines, threads, ripples and other forms, which are widely used in architectural decoration, furniture, mechanical equipment and other fields.

9. Spraying

(1) Covering the surface of stainless steel with paint, lacquer or wax to form a protective layer.

(2) Common spraying methods include manual spraying, automatic spraying and electrostatic spraying.

10. Transparent nano coating: The coating is usually composed of nanoparticles and has high hardness, wear resistance and corrosion resistance.

Widely used in the automotive industry, electronic appliances, architectural decoration, medical equipment and other fields.