When it comes to achieving optimal performance from SilcoTek’s high-performance CVD coatings, every step of the process matters - from design and fabrication to final installation. Welded assemblies, in particular, present unique considerations when preparing parts for coating. In this post, we’ll walk through best practices and technical tips to ensure your welded components are coating-ready.
1. Welding, Brazing, and Soldering & Coating Compatibility
Welding, brazing, and soldering are common methods for joining parts, but not all joining techniques or filler materials are ideal for coating afterwards.
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Heat Resistance: SilcoTek's CVD process requires high temperatures (up to 450°C), which most welded assemblies and braze joints can tolerate. However, it's crucial to ensure that welds are free of low-melting-point materials or weak joints that could deform during processing. Because soldering processes are typically performed at lower temperatures, it is important to identify if your soldering materials have a lower melting point than our coating process. The lower application temperature of solder means that the joint will likely fail when exposed to elevated process temperatures. The resulting joint failure may also contaminate the process and result in compromised coating quality. Because of this, soldered parts are not recommended for coating.
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Avoid Contaminants: Filler metals and welding fluxes can introduce impurities. These residues may inhibit coating adhesion or performance. Post-weld cleaning and passivation are critical steps. If possible, use high-purity, low-contamination welding techniques such as:
2. Design and Fabrication Tips for Welded Assemblies
When designing welded parts that will be coated, keep these best practices in mind:
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Minimize Complex Geometries at Welds: While SilcoTek’s coatings are conformal and can handle intricate surfaces, smoother transitions and fewer recessed weld areas help improve coating uniformity and consistency.
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Surface Prep Is Critical: A clean, metallic surface improves coating adhesion and functional performance. Before coating, ensure joined areas are free of:
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Know Your Materials: SilcoTek coatings adhere best to metallic surfaces like stainless steel, titanium, and alloys. Verify braze and material compatibility early in the design phase.
3. Post-Weld and Pre-Coating Cleaning
Weld discoloration and oxidation must be removed prior to coating. Recommended practices include:
If uncertain, SilcoTek’s technical team can advise on cleaning protocols or perform in-house surface prep.
4. Visual and Performance Expectations After Coating
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Aesthetic Differences: Welded areas may appear slightly hazier or matte after coating. This is typically due to microstructural differences or surface roughness around the weld. It’s cosmetic and does not affect performance.
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Function First: SilcoTek coatings provide outstanding corrosion resistance, inertness, and thermal stability - even on complex welded geometries - so performance remains consistent across the part.
5. Installation Tips for Welded and Coated Assemblies
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Avoid excessive mechanical stress on coated welds during installation.
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Do not use leak detection sprays that could damage the coating.
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For fittings and valves, always follow manufacturer torque specs to prevent microcracking of the coating near weld seams.
6. Can You Weld After Coating?
In short, it should be avoided. SilcoTek coatings are applied through a high-temperature chemical vapor deposition (CVD) process that forms a durable, conformal layer on the surface of the part. While these coatings offer excellent corrosion resistance and chemical inertness, they are not designed to withstand the intense, localized heat of welding operations after application.
Why Welding After Coating Is Not Recommended:
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Thermal Degradation: Welding temperatures can exceed 3,000°C at the arc, far above the thermal stability limits of SilcoTek coatings (typically 450°C or below). This will destroy the coating in and around the weld zone. The extreme temperature associated with welding will remove the SilcoTek coating approximately 2-4 mm in all directions from the heat affected zone.
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Contamination Risk: Heat from welding can burn the coating, releasing particulates or residues that may contaminate the weld joint and adjacent surfaces.
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Delamination: Localized expansion and contraction during welding can cause the coating to crack, flake, or delaminate from the base material.
If Welding After Coating Is Unavoidable:
In rare cases where post-coating welding is necessary:
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Limit heat input and avoid prolonged arc time.
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Mask or fixture the coated areas to minimize heat exposure.
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Be prepared to strip and re-coat the entire part or at least the affected area afterward. SilcoTek can reprocess most substrates, but you should consult our technical team first to assess feasibility and cost.
Final Thoughts
Welded parts can be excellent candidates for SilcoTek coatings, provided they’re fabricated with coating compatibility in mind. By choosing appropriate welding or brazing methods, ensuring proper surface preparation, and understanding coating behavior, you can unlock the full performance potential of your coated assemblies.
Have questions about your joined parts? Please contact our team for more information!
