A lot of DIY welding enthusiasts and professionals who work with stainless steel know that the metal gets tinted during the heating and welding process. This can diminish the aesthetic look of their finished project and make it look amateurish.
This is why many welders want to know how to clean stainless steel after welding?
The best way to clean stainless steel after welding is through a process called electropolishing. This process involves the oxidation of an acidic electrolyte on a metal surface with the help of electricity.
Electropolishing not only clears the surface from stains, but it also helps the metal become properly passivated. This covers the surface with an iron-free chromium oxide layer and gives it the shine that stainless steel is famous for.
What Are Heat Tints and Corrosion
Most metals, including stainless steel, have an oxide layer at the surface. Heat tinting causes this naturally occurring oxide layer to become thicker which causes discoloration. The temper colors are a direct result of light interference effects as light bounces off the metal surface.
Light reflected from the oxide film’s normal surface and that which is reflected from the oxide metal interface created by welding cause a variety of colors depending on the oxide layer thickness.
In the welding industry, various terms are used to describe this phenomenon, such as discoloration, oxide scale, and rainbow effect. All these terms are talking about the same thing, a change in the color of the top layer of stainless steel. It usually occurs around the weld bead and within the surrounding zone that has been affected by the heat.
Corrosion is a natural, oxidation process. When you prepare a metal surface for welding, it becomes exposed to a variety of atmospheric elements like oxygen and humidity, which creates the perfect condition for rusting.
This is why it is important to clean and polish your welding projects before and after the welding job. This helps preserve the surface, strength, and shape of steel structures. The increased durability and attractive appearance of finished steel projects are additional benefits of the cleaning process.
Types of Weld Cleaning
There are three main types of cleaning used for stainless steel after welding; mechanical, chemical and electrochemical. Brushing is used to prepare the surface and remove particles after cleaning.
Mechanical Weld Cleaning
Mechanical weld cleaning is a common and low cost method used for cleaning stainless steel. It involves grinding machines and abrasives to clean the top layer of metal surfaces where rust and other slag particles can form.
Mechanical welding consumes a lot of time and rarely achieves 100% clean results with necessary aesthetic value. It is only good for surface areas that are easy to reach.
Chemical Weld Cleaning
Chemical cleaning is the most commonly used method for metal cleaning. It involves using a chemical pickling paste for cleaning after a welding job. The paste is applied to the affected areas using a brush or spray and left on the surface for some time to interact with the metal. It is later removed and the surface is neutralized with a neutralizing agent.
This process is quite effective for cleaning steel after fabrication but welders don’t like it for a couple of reasons.
First, chemical pickling paste contains a variety of toxic acids, including hydrofluoric, nitric, and sulfur acids. These chemicals are quite dangerous for the human body and they can cause serious, long-term damage to the skin and internal organs if they are consumed or breathed in.
Second, only a certified operator is allowed to use chemical pickling paste. The operator’s whole body must be fully covered so that there is no chance of contact with the acids. This is why pickling is generally only used in commercial workshops and automated sites.
Electrochemical Weld Cleaning
Electrochemical weld cleaning, also known as electropolishing, is considered the most effective method of cleaning stainless steel. It is faster, safer and preferred by welders, compared to the other two methods. It doesn’t pose any major health risks for the welder.
Apart from post-welding cleaning, the process is also quite effective for removing rust, cross-contamination and other kinds of impurities from metal surfaces.
Electrochemical Cleaning Process
The process of electrolytic cleaning is extremely simple.
The welded metal piece is submerged in a mild electrolytic cleaning fluid. An electric circuit is formed by passing current (AC/DC)) through the electrolytic solution. This process helps clear impurities from the weld, removing discoloration and creating a desired level of passivation.
Different Types of Electrochemical Cleaning
There are two types of electrochemical cleaning that are used in welding. Both follow the same underlying principle of moving electricity through the weld to remove discoloration.
The first involves a manual application of electrolytic liquids to the workpiece using a carbon brush. Electricity is moved through the metal which reacts with the electrolytic liquid and creates a uniform, clean surface.
The second method involves using special electrolytic baths where metal parts are immersed in electrolytic fluids. When electricity passes through this mixture, it creates a chemical reaction that removes welding contamination or rust from the surface.
Benefits of Electrochemical Cleaning
You can use both electrochemical methods to clean stainless steel after welding. Each of them offers various benefits for welders.
Flexibility and Ease of Application
Electrochemical cleaning is easy to perform anywhere because the equipment is quite portable and easy to move around. You can perform manual electrochemical weld cleaning with the brush on site, off site and anywhere in between.
Electrochemical cleaning is also effective for all types of welding joints, including under-welds and surface joints.
Electrolytic fluids do not contain hazardous chemicals like pickling paste. It only contains a mild phosphoric acid that you would also find in common soft drinks. The main interactive agent is electricity rather than the electrolytic chemical itself.
This makes electropolishing very safe, and it can be used by both DIY hobbyists and professionals. Although you do require some protective equipment, like gloves and apron to keep yourself clean, highly protective suits are not necessary for electrolytic cleaning.
Speed of Application
The electrochemical weld cleaning process doesn’t take a lot of time. If you have the equipment prepared, it takes half an hour to get the whole workpiece cleaned, from end to end.
Good electropolishing apparatus will clean and passivate a metal surface at the same time and you don’t need to carry out any repetitive tasks.
Optimal Corrosion Resistance
Mechanical and even chemical cleaning does not protect against future corrosion for the metal. Welding equipment research suggests that the electrochemical process provides the best corrosion resistance compared to other cleaning methods due to its passivation effect.
Electrochemical Weld Cleaning for Stainless Steel
Electrochemical weld cleaning is particularly effective for cleaning welds created with stainless steel. Most welders choose to work with stainless steel due to its better durability, maintainability, appearance, and higher resistance to corrosion. They want a good way to clean welds after fabrication to maintain these fine qualities of steel.
If you compare stainless steel to other steel alloys, it has a unique ability to fight corrosion and preserve the structural integrity of the metal. However, it is still far from being completely rust-resistant. If you don’t clean the surface properly after you finish the welding job, even stainless steel can lose its structural integrity and become exposed to rust.
Most types of stainless steel are equipped with a passive surface layer to remedy this. This layer separates the iron base underneath from interacting with moisture in the environment. This is what prevents corrosion and rust from forming on steel surfaces. When you clean the stainless steel surface after welding, you should also ensure that the surface layer is repaired.
The electrochemical cleaning process carries out surface passivation at the same time as cleaning which means you will effectively finish both processes at the same time.
With electrochemical cleaning, you will be able to successfully remove different types of weld contamination – heat tints, discoloration, and rust, etc – and protect the surface from future corrosion at the same time.
How do you remove discoloration from stainless steel?
During the welding process, stainless steel is heated to a very high temperature that turns the metals into different colors like gold, red, purple, blue, or brown – depending on the temperature. While these colors may look pretty, they reduce the composition and oxidation properties of stainless steel.
Various methods can be used to remove discoloration from stainless steel after welding. The most common among them are electrochemical cleaning, chemical pickling, mechanical grinding, and brushing.
What is the best cleaner for stainless steel?
Electrochemical cleaning is considered the most effective method for cleaning heating tints and discoloration because it successfully removes oxides from the surface and restores the anti-corrosive, passive layer that keeps the metal protected.