More than other metals, stainless steel is used in many applications that require high levels of cleanliness and sanitation. Hospital equipment, medical tools, food service equipment, and restaurant kitchens are only a few common uses for stainless tubular steel products.
Corroded stainless steel will not meet those high standards of cleanliness. Even in non-sanitary work and rough industries, such as structural and industrial applications, corrosion means a metal can't do its intended job properly. Corroded structural steel has a much higher chance of failure than a clean, protected tube.
So, no matter your industry, you can either have your manufacturer take steps to prevent corrosion during the manufacturing process. If the corrosion process has already begun, you can remove the corrosion and then take preventative measures. Either way, corrosion should be dealt with as soon as possible to prevent damage and disasters.
Prevention
Generally, stainless steels will not break down in indoor environments, as they are strictly climate controlled. However, other steels and other environments always require preventative measures. If you want to make sure your stainless steel is highly protected, you should look into corrosion prevention at the beginning of the manufacturing process.
Choosing the Right Alloy for Your Application
Sometimes, corrosion can be completely avoided by choosing the right steel alloy for your project.
High chromium & molybdenum steels, such as 316 and 317, are the most resilient option for outdoor & marine environments. 304 is fine for mild exterior applications. 430 can hold up to a somewhat stressful indoor environment, such as shopping malls where the outside gets tracked inside.
However, the more chromium in the steel, the more expensive it will be. You'll have to balance the price of a durable steel alloy against the risks of frequent tubing failure.
Passivation
Passivation, in theory, occurs naturally on the surface of the steel. A protective film is created when the metal is exposed to the atmosphere, though it's often exposed to contaminants before the film can build up.
To ensure full passivation coverage, manufacturers can synthetically activate the process with a special acid bath. Depending on the steel, it may be submerged in nitric acid, nitric acid with sodium dichromate, or citric acid.
Coating
Coating your tubular steel can prevent and decrease the rate of corrosion. Powder coating and traditional paints are both viable, though powder coating lasts longer and is more durable overall.
Cathodic Protection
In infrastructure applications, steel structures can be protected with the help of a sacrificial metal and, in some cases, an electric current.
Galvanization is a simple version of cathodic protection. The steel is covered in a zinc coating, which will corrode in place of the steel. Even if a small bit of steel becomes exposed, the zinc will still take the brunt of the corrosion. This phenomenon is called preferential corrosion.
Heavy duty forms of cathodic protection involve the sacrificial metal (zinc or other anode) and an electric current. The current creates a more noticeable difference between the charges of the base metal and the sacrificial metal, forcing the sacrificial metal to take the brunt of any corrosion that occurs. This extreme type of protection is usually reserved for extremely harsh applications, such as marine and offshore environments.
Jacketing
Jacketing places a physical "jacket" around the steel tubing to protect against corrosion. Instead of galvanization or a coating that adheres to the metal's surface, the jacket is wrapped around the steel rather than bonded to it.
Plastic or Rubber Connectors
We talked about bimetallic corrosion in Part 1. This type of corrosion can be avoided by using non-metal connectors, such as nuts and washers, when you need to connect two different types of metal.
Removal
Abrasive Blasting
Abrasive blasting is a cost-effective corrosion removal method for industrial parts and large order sizes. There are different blasting materials (glass beads, metal shot, sand, water, etc.) that are effective for both industrial and more delicate products. Blasting is often a precursor to powder coating or painting.
Chemicals
There are certain chemicals, such as naval jelly and oxide cleaners, that remove rust without damaging the metal's surface. For large orders, this removal method may not be the most cost effective.
Pickling (Descaling)
The descaling or pickling process is very similar to the passivation process we outlined above. The biggest difference is when you do it (before or after corrosion occurs).
The pickling acid you use will depend on the type of steel you have. Different steels build up scaling with different chemical compositions, and different steels react differently to each pickling acid. The most common acids are nitric, hydrofluoric, sulphuric, and hydrochloric.
Cleaning
Once you've removed the corrosion from your tubular steel products, they need to be thoroughly cleaned before a protectant can be applied. Cleaning removes any chance of debris (stencil marks, fingerprints, lubricants, etc.) getting stuck between the metal and its protective coating.
Most manufacturers will use alkaline, electrolytic, or solvent cleaners. After cleaning, the metal is taken to be galvanized, passivated, or whichever preventative method you choose.
Home Cleaning and Protection
If you're looking at a small spot of corrosion (or you don't have the budget for industrial cleaning), there are ways to remove it on your own. When scrubbing steel, most experts recommend a wire brush to remove large debris, then fine sandpaper for getting the difficult areas without scratching the metal's surface.
Once you've scrubbed the corroded area, you can clean the area further with naval jelly (which dissolves rust) or another rust removal chemical.
There are a number of industrial-strength rust removal chemicals available through Amazon and other online retailers. You can find a variety of cleaners that cover all needs - even organic cleaners for the environmentally conscious. You can even create your own at home with baking soda and water. Most industrial cleaners contain oxalic acid, which is tough on rust and stains and easy on the steel itself.
When cleaning corrosion from steel, be as thorough as you possibly can. Metal corrosion is like having a cavity - if you don't get it all, it'll come back and cause problems very quickly.
After you've removed all traces of corrosion, you can apply a protectant of your choice. There are plenty of polishes, sprays, paints, and primers available online.
Interested in Tubular Steel Cleaning Services?
If you've got some tubular steel products that aren't looking so good, we provide bead blasting as well as powder coating and other finishing services. The larger your order, the more cost-effective our industrial services will be.
