Weld penetration is arguably the most important variable in welding. Weld penetration has always been measured with destructive testing in conventional welding, but are there better alternatives? How can you tell if a weld has good penetration?
There are destructive and nondestructive ways to check if a weld has good penetration. In conventional environments, you’re likely to test for penetration by cutting and stress-testing. However, non-destructive alternatives like x-rays and hydrostatic tests are more common in industrial settings.
In this article, you’ll learn some of the factors that affect the penetration of your weld. Also, you’ll learn the common destructive testing procedures to tell if a weld has good penetration and some industrial and nondestructive methods to achieve the same objective.
Why Is Good Penetration Important in Welding?
When welders join metals, they aim for perfect penetration. When the metal joins together perfectly, the phenomenon is referred to as a complete penetration weld. The deeper and more complete the penetration is, the more resistant the metal will be to cracks and bends.
The best penetration occurs when you can join two metals successfully without leaving any gaps between them. While you should aim for this whenever you’re welding, you won’t always be so lucky.
If you can achieve near-perfect penetration, however, you’ll have a stronger overall weld. Since there are no spaces for cracks to start within your weld, it’s much harder for the metal to start to come apart from the joint.
The strength that comes from a good penetration makes it easier for the weld to hold up under pressure. This explains why most industrial welding prioritizes good penetration over most other qualities in welding.
A good penetration also makes the metal resistant to corrosion. When there is a little gap between two metals, it may accelerate corrosion. Since a perfect penetration leaves no gap between the metals, it’s typically more difficult to introduce differentials to catalyze corrosion in the weld.
Sometimes, you think you’ve nailed the secret of getting good penetration and your next weld will be a total mess. If you’re confused as to why this happens, you may want to continue reading on to the following sections.
Before learning how to check if your weld penetration is good enough, it’s important to learn some of the factors that make or break your weld penetration.
Factors that Affect Weld Penetration
Many factors affect weld penetration. With experience, you’ll come to learn how to get the perfect penetration in your weld, creating perfect joints. Here are some of the variables that have a direct effect on the penetration of your weld.
- Amperage
Some welders will tell you that weld penetration is all about amperage. From that statement, it’s easy to understand that amperage is the single most important factor contributing to weld penetration, regardless of what you hear elsewhere.
Generally, your amperage is directly proportional to the penetration. While you may want to use the highest amperage for every condition, the myth that you can’t have too much penetration is just untrue.
If you adjust the wire feed speed to allow too much amperage, you’ll run into some problems. In the worst-case scenario, you could punch through your base metal, destroying your entire weld.
- Travel speed
When welding, it’s always safer to go slowly. The faster your travel speed, the less likely it will be to achieve a decent penetration. There is a specific range of penetration that you should try to keep to make your weld look passably good.
If you slow down too much to increase the penetration, you’ll lose the penetration completely. Welding is all about achieving balance; there is no specific setting that makes it right 100% of the time.
- Voltage
Voltage doesn’t have as much effect on penetration as amperage, but it’s something you should keep your eye on. While it’s easy to get the correct voltage, welding at a high voltage will decrease the penetration.
Since the system expends more energy density with increases in voltage, the decrease in penetration is very understandable. Setting your voltage to very low values will only lead to a useless arc which will lead to lost penetration. In this situation, you need balance.
- Technique
Sometimes, all of the factors that affect your penetration will be controlled by your welding technique. In these cases, you’re at the mercy of your technique, making it impossible to get a decent penetration even if you want to.
While there are no techniques that guarantee bad penetration, it’s more difficult to achieve perfect penetration in some techniques over others. If you’re just starting, it’s recommended to use mainstream techniques, as they’re usually less prone to mistakes compared to complex ones.
How Do You Know If a Weld Has Good Penetration?
If you have all the factors controlling the penetration of a weld under control, you should also learn how to check if your efforts are bearing fruits. Interestingly enough, the advent of technology hasn’t given a reliable way to check weld penetration non-destructively in everyday scenarios.
If you’re working with industrial metals, you wouldn’t want to be cutting through steel and you don’t have to. Here are all the ways to determine if a weld has good penetration, classified into destructive and non-destructive methods.
- Destructive methods of checking weld penetration.
If you practice the typical type of welding where you join metals for common tasks, you’ll likely be using destructive methods to check weld penetration.
Destructive methods may include cutting through the weld and observing with your eyes, using chemicals to check the strength of the weld, bend testing, and stress testing. All of these methods work, but they destroy the weld to give the desired information.
- Non-destructive methods of checking weld penetration.
In industrial environments, welders prefer checking if a weld has good penetration using non-destructive methods. The most common non-destructive penetration test for welds is X-ray testing, which is next in popularity to the destructive testing methods.
X-rays can determine the presence of a fault, its location, and its depth without dealing any damage to the weld. In addition to x-rays, hydrostatic tests can also test the penetration of a weld nondestructively.