Sustainability is one of the biggest buzzwords at the moment. There is a huge focus on making everything more sustainable, from vehicles to construction, manufacturing to energy generation. One of the crucial things is to use products that can offer a long service life. Reducing the need for repairs and replacement can save a lot of resources and energy. ERW tube can be a fantastic choice for many applications. However, you need to ensure there are no issues, particularly tensile residual stress. Let’s have a closer look.
What is it?
High frequency electric resistance welded tubing is a fantastic product. It is cost effective, has good tolerance, and comes in a wide array of different shapes and sizes. You can use it for a variety of applications, or do additional processing to adapt it. Hydroforming has become especially popular because it can use internal pressure to create complex shapes from the tubing. This can dramatically reduce the number of separate parts and welds or connections in different products.
The problem with HF ERW tubes is processes to create it, and additional secondary processes like hydroforming, leave tensile residual stress. It tends to be highest in the weld itself and the heat affected zone (HAZ) around it. Then, it gradually lessens as you move closer to the unaffected parent material.
The big problem with tensile residual stress is it can cause ERW tube failure in the future. This may happen during secondary processing, including bending and hydroforming. It can also occur once the tube is in service, creating an even higher risk.
Three issues
Studies show that there are three main causes of residual stress in ERW tubing. Firstly is plastic deformation, typically occurring during cold forming such as rolling a sheet or strip of steel into a tubular shape.
Solidification and the solid-state phase transformations are the other two causes. High frequency welding changes the state of the parent material, heating it quickly to allow both edges to join. It can result in some big problems though. Crystalline changes are especially problematic because they cause volume change and can mean higher levels of tensile stress in different spots. A change of texture can be a major problem too. Goss and cube textures mean a significantly higher risk of cracking.
How to avoid problems?
As you can probably see, in the search to improve sustainability, it is important to use ERW tube with a lower risk of failure. It provides many advantages, including a longer, more successful service life, as well as less downtime and higher safety standards.
There are a couple of different ways to address tensile residual stress. First is modification of the weld sequencing. There are a few crucial things to keep in mind that influence the welding quality. Most important is the heat and squeeze pressure. The latter must avoid the entrapment of oxides like black iron oxide.
Secondly, and more importantly, is post weld normalisation. The goal here is to get rid of stress, detrimental structures like bainite, and unwanted textures like cube. It can provide big benefits, including improving toughness.
Do you want to order high quality ERW tube?
Union Steel Tubes understands the importance of sustainability. It is a core part of our business, including our approach to creating tubing and using resources carefully. We do a lot of good here, such as keeping scrap and waste as low as possible.
So, if you want ERW tube for any kind of applications, speak to us. We’re always happy to provide advice, and have a wide selection of tubing to ensure we can offer products for most needs. In fact, we have a variety of round, oval, square and rectangular tubes in different diameters and wall thicknesses.
