Not much upsets a professional welder. They’re a tough breed. And if one was to get a little dewy-eyed behind that mask we’d never know. But what we do know is, nothing sends a chill down a welder’s spine like seeing cracks in the welds they’ve so painstakingly made.
Weld cracks are frustrating for the welder and welding engineer. On metal fabrication jobs where welding must be done to code, there’s often no option but to start again. Even if it is possible to rework the joint and save the material, cracks waste the time of everyone involved. That’s why the whole team here puts a lot of effort into crack prevention and maintaining weld quality.
The only way to prevent weld cracks is to understand, and then eliminate, the factors that cause them. Here’s what we know and what we do.
Types of Cracks
Cracks that have formed in welds are described in many different terms. The first division or classification is whether they are hot cracks or cold cracks.
Hot cracks are formed while the weld and material are cooling. Cracks that occur later are called cold cracks.
Hot cracks are almost always caused by problems with how the weld is being made. They might be due to how the weld is designed, poor preparation, incorrect fit-up, or technique. Cold cracks may result from how the weld was made, but they can have other causes. Fatigue and high stresses are two examples and their root cause goes back to the design. Corrosion is another contributing factor in cold cracks.
When cracks occur in the weld itself they’re usually longitudinal or centerline cracks. These run along the weld bead or filet. Transverse cracks, running across the bead, are less common and may result from overloading or fatigue.
Welding can also create cracks in the heat-affected zone (HAZ) of the base metal. These are usually hot cracks because they show up as the joint cools. They may however take some time to occur, making them technically cold cracks.
The Causes of Weld Cracks
A crack is a region where the metal has been torn apart. This happens when the stresses acting on the joint are greater than the strength of either the base metal or the weld metal. You might think that means every crack results from poor design because the strength of metals is well known and readily available, but that overlooks the impact of heat.
When you make a weld you melt the base materials and the filler you’re adding to the joint. When the base metals are the same alloy the weld pool is similar too, although the filler might change its composition a little. If you’re welding different grades or specifications, the weld pool becomes an alloy of both, potentially with different properties. These properties include strength and coefficient of thermal expansion.
Each piece being welded expands as it heats up, and shrinks as it cools back down. However, at some point, the weld pool solidifies, which locks the pieces being welded into place. It doesn’t stop them shrinking though. That continues, which puts stress into the joint.
Another cause of cracking is hydrogen embrittlement. This changes the composition of the base metals, making them weaker and so more likely to crack under high stress. It’s particularly common as a cause of HAZ cracking. And if you’re wondering where hydrogen comes from, the answer is water.
Understanding Fatigue and Corrosion Cracks
Fatigue and corrosion cracks take time to develop. While technically cold cracks, it seems unfair to lump these into the category of cracks that occur within days or weeks of a piece being welded. These are more likely to occur because the long-term strength of a weld wasn’t initially produced or premature corrosion of the weld occurred for a variety of reasons.
Cracks like these are best prevented by an experienced team of skilled welders and engineers. Understanding the dynamics of how metals, alloys, and welds work in concert, they’re able to achieve the optimum quality of weld that will last a long time.
Preventing Weld Cracks
Cracking is always a topic of conversation in metal fabrication shops, and that includes here at Wiley Metal. We strive for perfection but welding is still mainly a human endeavor. Especially when it comes to challenging welds and projects things can go wrong, and that leads to flaws or the occasional crack.
There are many things we do to avoid cracking. We strive for cleanliness and take good care of filler metals to avoid hydrogen embrittlement. Projects that use multiple alloys are monitored especially closely because of how that can influence the strength of the weld. We do a lot of pre-heating to minimize shrinkage issues, and we take great care over the fit-up of parts prior to welding.
A major part of avoiding weld cracking goes back to fabrication or weldment design. Making a good weld is about managing the weld pool. That depends on arc length and orientation and the speed with which the arc is moved. All of these require that the welder can (a) see what they are doing, and (b) position the torch as needed.
The ability to do these depends on how the part is designed. We’ve heard many stories of engineers with no welding experience designing parts that couldn’t actually be welded or where the welder was effectively blind, relying on feel to put the arc where it needed to be.
To avoid problems like these our engineers look closely at weld design, weld location and even the metallurgic makeup of the material(s) used. This is where experience really pays off. The more welds that a metal fabrication company performs and the more different metals and alloys a fabrication company is used to dealing with, the more likely they have determined how to minimize cracks of any type.
You’re Only as Strong as Your Weakest Link
A chain is only as strong as its weakest… well you know, and the same goes for products, companies, and teams. We’re of the opinion that there’s no better example of this than in welding. Some people view welds as a potential source of failure but at Wiley Metal we view them as a source of strength.
When we take on welding projects we’re determined to make sure our welds won’t crack or fail. Instead, we expect them to add to the strength of the piece we produce. Our engineers and welders are dedicated to making sure every weld that leaves Wiley Metal will meet and exceed expectations both in the short and long term. In fact, we guarantee it.
Our Quality Weld Team Avoids Cracks
It’s pretty simple. Since cracks are such a source of exasperation for our team of welders, engineers, and quality control folks, we work together to avoid them at all costs. (We were going to use a stronger word than “exasperation” but they asked us not to say that cracks have caused strong men to shed tears of frustration.)
We’re not perfect but we do have decades of experience to rely upon. Welding is all about skill, experience, metallurgy, and engineering, and we have an abundance of those. That’s why you can count on the Wiley team to deliver. Let us know what we can do for you.