High frequency welding is one of the best advances in the history of tube manufacturing. It results in higher quality welds and massively reduces production time. However, it isn’t all positives. The main issue is it can result in residual stress in ERW tubes. That can lead to a number of serious problems, including tube failure in some situations.
How does it happen?
The issue with residual stress occurs mainly because of cold working. Generally, working at room temperature offers a number of advantages. For example, it can produce parts like tube economically with less waste. Products will be strong and consistent. The production speed is impressive, especially if you include automation.
What you need to keep in mind is cold working results in plastic deformation. If it isn’t uniform, there can be a lot of stress. You can have areas where there is a high concentration of stress. Many materials also seek to return back to their previous shape. This is known as springback. It can be a bigger problem with cold working. Then, when you weld, there is residual stress as the materials still want to springback but can’t because of the bond.
The issues
As we said above, residual stress can result in failure in ERW tubes. It is especially likely to happen if you do additional processing such as tube flattening. The main concern is it can lead to cracks at grain boundaries, compromising the strength.
The residual stress can also cause a number of other issues. Most importantly, it can reduce the service life because it increases fatigue. This can be a big problem, especially for automotive and industrial applications; the last thing people want is expensive repairs and replacements.
Finally, residual stress can also lead to issues with corrosion. The problem here is it increases the chemical reactivity. You also have a higher risk of cracks developing. They allow corrosive elements to penetrate into the material. Ultimately, you may have big problems with corrosion.
What to do?
Luckily, there are a few things that can improve residual stress, including in ERW tubes. Most importantly, you should look at post weld heat treatment. Normalisation can have a really positive impact because it improves the microstructure. In turn, it can make the weld tougher and reduce the risk of cracks.
You also need to ensure the welding parameters are correct. The heat is critical, ensuring you get the sweet spot to avoid issues with too much or too little heat. The squeeze pressure must be right to ensure you don’t trap oxides; they can lead to failure.
It may be necessary to do destructive and non-destructive testing to evaluate the residual stress in components, especially tubing. There are a number of different methods to try. However, keep in mind that any destructive methods will require sacrificing products.
Do you want to order ERW tubes?
Union Steel Tubes has built a fantastic reputation as one of the most consistent tube manufacturers in the UK. We have very high standards, and strive to give every client a friendly, professional service. Even more importantly, we are always ready to share our knowledge to ensure clients choose the right tubing for various applications, factoring in things like service life.
So, if you need ERW tubes, speak to us. We have a broad selection, with shapes and sizes for almost any project you can imagine.
