Knowing how to clean stainless steel after welding is a vital skill all welders should master. Stainless steel welds tend to become tinted after the welding process and are prone to corrosion. To avoid this, cleaning stainless steel after welding involves removing the discoloration and finishing the weld. This article will let you know how to clean stainless steel welds.
Cleaning stainless steel after welding is vital because a colorful weld is below par. The alloys in the steel react, causing a rainbow appearance with hints of gold, blue, brown, or red in the weld. Although the weld may look attractive, the tinted weld surface is more liable to corrode.
What are the most effective ways to clean steel welds to avoid tinting? Although pickling paste is a tried and trusted method of cleaning stainless steel after welding, are there better ways? Please read on to find out.
Why Stainless Steel Tints After Welding
So, what causes stainless steel to tint as it cools after the welding process? Discoloration occurs when the alloys in steel react during the welding process. The level of tinting depends on the amount of heat used during welding, the alloys in the steel, and the welding speed.
Stainless steel contains iron, carbon, and chromium. It’s the last alloy—chromium—that gives stainless steel its durable, non-rusting properties.
Welding affects the structure of the steel, and a chemical reaction occurs. The chromium separates and comes to the surface. The result is that the outer layer of steel loses its transparency and a rainbow effect on the steel appears.
But is the change in color just a cosmetic issue? Or is the rainbow appearance something to be concerned about?
Reasons Why Stainless-Steel Welds Can Corrode
Steel welds with a rainbow effect are prone to corrosion because the weld is depleted of chromium. This means that unless you remove the oxidized layer, it’s impossible to restore the passive protection of stainless steel. Therefore, appropriate weld cleaning is crucial to prevent the steel from rusting.
So, the causes of stainless steel corrosion are due to oxygen in the air penetrating the oxidized weld. In time, the compromised weld can show signs of corrosion unless thorough cleaning is done.
How to Clean Stainless Steel After Welding
The different methods of cleaning stainless steel after welding include chemical pickling, electrochemical cleaning, and mechanical weld cleaning. Each of these weld-cleaning methods has its advantages and disadvantages. In addition, some types of stainless steel weld cleaning methods are better for different welds.
Here are the three primary methods of weld cleaning for stainless steel.
Chemical Pickling to Clean Stainless Steel Welds
To clean a stainless steel weld, you can apply a chemical pickling paste to the weld bead. You need a spray or brush to apply the chemical solution. The toxic acids interact with the metal to restore its passive protective layer. After that, you use a neutralizing agent to clean the surface.
The issue with using pickling paste for cleaning stainless steel welds is that it’s highly toxic. The combination of sulfur, hydrofluoric, and nitric acids can cause severe damage if mishandled. That is why only certified welders can use chemical cleaning on welds.
Chemical weld cleaning equipment required: Protective gear, pickling paste, a brush or spray bottle to apply the paste.
Pros of chemical weld cleaning: It’s relatively inexpensive and ideal for occasional use. You can use it for welded parts that can’t be submerged in a bath.
Cons of chemical weld cleaning: The pickling paste is highly corrosive, and the nasty acids can cause damage to the skin and internal organs. Therefore, great care is required in using strong acids. Additionally, the welding areas must be vented to prevent lung damage from inhaling toxic fumes.
Electrochemical Cleaning Process for Removing Heat Tints from Stainless Steel Welds
The electropolishing method is the most effective way to remove burn marks from stainless steel after welding. The electrochemical cleaning process involves submerging the welded piece in electrolytic cleaning fluid. Then an electrical current is passed through the solution to clean impurities from the weld. This restores a passive protective layer and removes discoloration to prevent corrosion.
Typically, most welders choose electrochemical cleaning on stainless steel after welding. This weld-cleaning method has fewer risks and is highly effective for eliminating impurities from metal surfaces.
Electrochemical weld cleaning equipment required: Electrolytic fluids and an electrochemical cleaning machine to submerge items in the electropolishing solution.
Pros of the electrochemical method: The process is safer than applying pickling paste and results in a bright, mirror finish.
Cons of chemical weld cleaning: Although it’s excellent for effective cleaning after welding, it’s expensive and unsuitable for large parts.
How to Remove Weld Burn Marks from Stainless Steel Using Mechanical Cleaning Methods
The mechanical method is the cheapest post-weld cleaning process to remove a heat tint from stainless steel. This cleaning process involves grinding the top layer of metal to remove rust and other slag particles. Then, using abrasives, a wire brush, or a grinder, you can safely remove any tinting or discoloration from the metal surface.
Typically, using mechanical methods for cleaning stainless steel is the least effective. This is because it’s rare to achieve a perfect surface, and it usually only improves the aesthetic appeal of a stainless steel weld.
Equipment to clean stainless steel welds mechanically: Any type of abrasive equipment—steel wool, wire brush, or angle grinder.
Pros of mechanical weld cleaning: You probably already have the necessary equipment, and it’s a low-cost cleaning method.
Cons of mechanical weld cleaning: The cleaning process is labor intensive, and it’s challenging to remove all impurities. Additionally, it can weaken the weld strength and may develop rust after a while.
Clean Stainless Steel After Welding — FAQs
Let’s discuss some of the most frequently asked questions about how to get polished, shiny stainless steel welds without a hint of tinting or burn marks.
Does Welding Ruin Stainless Steel?
Welding can affect the anti-corrosive properties of stainless steel. This is why it’s crucial to prevent damage to stainless steel surfaces after welding by cleaning the weld. This requires mechanical, chemical, or electrochemical cleaning to prevent contamination and re-passivate the stainless steel surface.
How do you Keep Stainless Steel from Rusting after Welding?
After welding stainless steel, it is crucial to remove heat tint and cross-contamination from the weld. You can achieve this by applying a solution like pickling paste or electropolishing to restore the steel’s anti0corrosive properties.
What Treatment is Recommended after Welding Stainless Steel?
Electrochemical cleaning is the safest and most effective method for cleaning stainless steel after welding. The process of cleaning welds uses a relatively safe acidic electrolyte solution and an electrical charge to remove contaminates from the weld bead. The result is excellent re-passivation of the stainless steel surface and a quality weld without the rainbow coloration.
Does Vinegar Remove Rust from Stainless Steel?
Vinegar is a simple DIY method to remove rust stains from stainless steel surfaces. However, the acidic solution is too weak to use for welding. Vinegar isn’t acidic enough to penetrate the metal surface and clean a stainless steel weld. You can, however, use vinegar to gently remove surface stains to keep stainless steel items looking good aesthetically.
Does Citric Acid Clean Stainless Steel?
You can use citric acid for cleaning stainless steel after welding. The acidic properties of citric acid work similarly to nitric acid to passivate welds and restore the integrity of stainless steel. However, before reaching for the kitchen cabinet, it’s good to remember that you need a professional citric-based formula designed for stainless steel weld cleaning.
What is Pickling Paste for Stainless Steel?
Pickling paste for stainless steel weld cleaning is a thick gel. It contains a toxic chemical formula containing nitric, hydrofluoric, and sulfuric acids. The chemical pickling paste is applied to stainless steel welds to remove heat marks from welded stainless steel.
What is the Difference Between Pickling and Passivation ?
Pickling stainless steel welds uses a highly toxic gel that removes the surface of the metal to treat impurities. This helps provide a sub-level change in the weld structure to ensure corrosion resistance and remove heat burns. On the other hand, passivation is less aggressive and doesn’t go beyond the metal’s surface.
Both passivation and pickling are suitable methods for increasing the durability of stainless steel welds.
Conclusion–How to Clean Stainless Steel After Welding
After welding, cleaning stainless steel is vital for achieving a highly polished look without discoloration on the metal. However, even more importantly, knowing how to clean a stainless steel weld is vital to ensure a highly corrosion-resistant weld that is strong and won’t crack. Therefore, the ability to weld, clean, and polish stainless steel is a crucial skill for any welder to master.