Passivation with Passion – Handheld Laser Welding and Cleaning Systems for Stainless Steel Passivation

Stainless Steel Passivation and Welding

Stainless steel, discovered in 1913, contains chromium that forms a thin chromium oxide layer on the surface, providing corrosion resistance. Passivation processes typically involve using nitric acid or citric acid to either create or facilitate the formation of this layer. Thorough cleaning is crucial to ensure contaminants, such as oils, spatter, or grease, do not interfere with the passivation process.

During stainless steel welding, heat input causes the material's color to change, indicating the formation of a heat affected zone. Depletion of chromium in this zone prevents the formation of the chromium oxide layer, requiring the removal of the oxidized layer to allow passivation to occur. Laser technology is now being used as a non-contact process to complement these methods and provide a cost-effective alternative.

Laser Cleaning: A Safer and More Precise Alternative for Post-Weld Passivation

Traditionally, pickling using strong acid solutions or mechanical methods like grinding and abrasive blasting have been employed for post-weld passivation. However, these methods have drawbacks such as toxicity, surface damage, and process variability. Laser cleaning with handheld laser devices offers an alternative approach that is repeatable, not affected by chemical degradation, and provides precise cleaning without line-of-sight limitations.

Laser cleaning involves rapidly scanning the laser beam over the joint surface, effectively removing oxidation from the weld joint. With handheld laser devices, the welding nozzle can be quickly exchanged for a laser cleaning nozzle, enabling cleaning up to 15mm wide. Tool-less tip exchange and preset cleaning parameters ensure consistent and reliable cleaning of various joint configurations. Laser cleaning also eliminates the need for hazardous chemicals and minimizes the use of abrasive media.

Sturbridge Metallurgical Services Test Conditions

The above image shows the comparison between two sides of a stainless steel coupon. The right side shows the piece after welding while the left side shows the piece after it was welded and laser cleaned.

Courtesy Sturbridge Metallurgical Services Inc.