In this article, we will discuss the nature of crater cracks, why they occur and how they can be repaired. If you aren’t familiar with welding, please read my welding article, as it covers the fundamental principles and terminology of the welding process. So, what are weld craters and crater cracks?
What is a Crater?
Before we look at crater cracks, let’s first understand what weld craters are. A definition of a crater in welding is an inadequate amount of molten metal used to fill the cavity, leaving a thin section. The inadequate amount of molten metal gives a crater the appearance of a circular excavated hole. Stopping the welding process prematurely is the usual cause of a crater. Finishing prematurely does not allow enough time for a sufficient amount of molten pool to fill the cavity. Craters revolve around the finishing stages of welding, meaning they are normally located at the end of welds.
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What is a Crater Crack?
As you’ve guessed, crater cracks form in craters. But why? As discussed above, craters tend to be at the ends of welds from premature termination of the welding process and are a common weld defect. The weld ends undergo the most amount of contraction when cooling, resulting in high residual stress. As a result, this makes them a weak point within a weld. However, when you create a crater at the end of a weld, you are causing it to be even weaker! Therefore, crater cracks form due to the weld pool not having sufficient volume, to withstand the stresses arising from shrinking. However, the defect will not necessarily form right after welding. Cracks can develop over time as the weld experiences stress such as tension, twisting etc. They may develop after one day, two weeks, three months or years!
Craters can be visually recognised by a concave weld profile (bead). A concave bead is a good sign that an insufficient amount of molten metal was used for the weld. In addition to craters, a concave bead is an attractive environment for centreline cracks to form.
How To Prevent A Crater Forming In A Weld
One of the best ways to prevent the formation of craters in welds is to use a runoff tag, especially on butt joints. This technique will remove the stopping portion of the weld on the joining materials.
Progressively reducing the welding current as the end of the weld approaches is also an effective method of preventing craters from forming in a weld. The current controls the amount of heat generated in arc welding, therefore reducing the current will reduce the size of the weld pool mitigated the likelihood of a crater forming.
How Are Crater Cracks Repaired?
Weld repairs are a common activity in engineering industries as they predominantly determine the life of steel structures (learn more here). To repair a crater crack, weld material is removed until the crack has disappeared. Grinding is the usual method to remove weld material. Once removed, the welding process will be repeated, filling the cavity with a sufficient volume of the weld pool to prevent a crater from forming again.
Summary
Welding is a widely used process in the engineering industry, and you are more than likely to experience it during your career. It is important that you understand the essentials of welding and understand the fundamental defects. We have discussed the definition of a welding crater and covered one of the common welding defects and discussed the fundamentals behind the defect. In addition to this, we can identify craters in welds while also knowing how to repair them.
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