May 27, 2022
We've spoken before about why it's so beneficial to call out ZRC by name in your specification sheets. While this is important to do for a variety of projects, this is particularly needed for your upcoming welding jobs. ZRC is ideal for welding and metal fabrication applications. Engineers and architects are setting up the entire project for success when they say “Just ZRC it!”
Why Welding Jobs Require Rust Protection
ZRC is something every welder should have in their bag or tool belt. This is because welding requires a barrier of protection. You see, dissimilar metals will always rust if you don’t treat it with something. The process of rust begins nearly immediately, as soon as oxygen, moisture, or humidity is present. Rust is the result of corrosion caused by oxidation in metal. The oxidation process eats away at the metal and creates visible rust on the metal's surface. The exact way the rust takes over your metal structure varies slightly, though, based on exactly what you're welding.
Welding Regular Steel
The lifespan of an uncoated metal that is susceptible to rust is significantly shorter than one that is coated with a zinc coating, either hot-dipped galvanized or coated with a cold galvanizing compound. This is particularly true if the metal has been welded together.
When you’re welding two pieces of metal with a welding rod and heat, you’re actually melting a little bit of the surface of the metals and mixing it with your rod. Depending on the exact material of your welding rod, this can make the welding area more anodic than the rest of the area.
During the process of corrosion, two reactions take place. One is the anodic reaction, mentioned above, in which metal atoms are ionized and pass into solution, leaving their electrons within the original metal surface. The opposite reaction is cathodic, meaning the free electrons within the metal are taken up by chemical species such as O2 and H2O in reduction reactions. In other words, when two dissimilar metals are touching one another, the less noble of the two metals will corrode to the cathode.
Let's say that you have zinc and steel in direct contact with one another. In this scenario, zinc is less noble and will become anodic and corrode to the steel. The less noble metal will always corrode first, in fact.
Welding Hot-Dipped Galvanized Steel
The above scenario described welding two regular pieces of metal. When you weld hot-dipped galvanized steel, the process isn't totally dissimilar. You have all the same problems, with another one added on.
You see, hot-dipped galvanized steel is called such because it has a layer of zinc protection. This form of metal is already protected from rust, right? This is not the case if it has been welded. When you weld metal like this, you’re melting off the very zinc layer which is protecting the steel. You’re also essentially oxygenating the steel. You still have zinc on the sides that haven’t been burnt off, though, and this creates a potential for it to rust severely and quickly. It directs all the rust to that one area, the weld!
In order to avoid this, you must regalvanize the areas where the zinc has been removed and welded together. Clearly, it makes sense to coat the weld with a ZRC product so that zinc protects the entire structure.
Welding Stress Fractures and Cracks
There is one other potential risk to keep in mind when welding. As you’re welding, if the metals get stressed on some way, it can cause stress fractures, cracks, nodules, and notches. These already-damaged areas will corrode. You can fix it after the project is finished; you need to relieve the stresses. This often isn't done, though, and so a ZRC product can be applied afterwards.
Changes to ASTM-A780
If you don’t take any methods to protect the metal, then the welds will rust. This has been known for many years, going all the way back to the 1950s.
The American Society for Testing and Materials (ASTM) wrote ASTM - A780 as guidance for use of zinc coating in the corrosion resistance of welds. Since the early 90's, they specified a zinc rich coating had to be a minimum of 92% zinc in the film in order for it to meet the industry standard. ZRC has met this since the 1960's!
Back in the early 2000's, the committee changed the specifications to now allow coating with less zinc. Due to industry lobbying, they announced that in addition to greater than 92%, just 65-69% zinc provided a barrier protection that was good enough in the short-term. Cheaper barrier paints could now be used, but at what long-term cost? Every day we encounter situations where inadequate protection was used to coat welds with disastrous results. Once the damage is done there's no turning back.
It is important to note that this newer standard allows use of a simple barrier coat. However, once it’s broken, like from heavy rain and years of weatherization, rust begins. In order to get something that is going to work well to protect the steel from rusting for decades to come, you must go with the higher 92% rating. The other option is nothing more than cheap, short-term barrier protection. Doesn't it make good sense to only use a repair product that will give the same protection as the original hot-dip galvanizing?
ZRC Galvilite® For Welding Jobs
Oxygen starts the corrosion process, and once it begins it doesn't stop on its own. The best way to halt it is to use a product like ZRC that will cover the surrounding area. An area of a metal structure that has been welded will always rust without a ZRC product. Your only real question is, which one? One we encourage you to pay special attention to is ZRC Galvilite®. It was designed specifically for field and shop repair of hot-dip galvanization. It is manufactured with the highest purity ASTM D520 Type III zinc dust. It meets VOC standards in all 50 states and exceeds galvanizing repair specifications.
ASTM may have decided that short-term protection that breaks down quickly is good enough, but we didn't. We stand by the older standards of exceeding 92% zinc for our products. This is one reason our Galvilite product is very important for those in the welding and metal fabrication industry. As soon as you make a weld, protect it with ZRC!
