A look at ERW bond lines

If you need steel tubing for a project, ERW tubes may be the perfect option for you. High quality products can suit an array of applications. For example, they are great for handrails, furnishings, and much more. You can find some of the finest tube here if you want to order some.

What is the ERW bond line?

ERW tubesIf you examine the cross section of an ERW tube you will see a line at the centre of the weld. It is known as the bond line. This is a point in the weld where the grain size and hardness can vary because the microstructure of the metal will be different.

The lines form at the centre of welds because of nonequilibrium phase transformations. They occur due to the high deformation rate here and the fact that the temperature tends to be the highest.

The thing to keep in mind about bond lines is they can vary in terms of the shape, width, and orientation. The actual shade can differ too. All these differences depend on the type of steel used to make the ERW tubes. The etching technique can have an impact too.

How hard is it?

An important thing to note here is the bond line can vary in terms of hardness. There has been a lot of research to look into this to see how it differs.

For one thing, the bond line is harder than material in the thermo-mechanically processed zone (or heat zone) with low alloy steel. That is because it is a mix of ferrite, bainite, and untempered martensite. It makes it harder and some believe that results in a loss of toughness. But, you can improve it by annealing after the welding.

The bond lines aren’t always harder though. In fact, they are softer with low carbon steels and stainless alloys. This is because of ferrite in the microstructure.

Is it a defect?

When people choose ERW tubes for a project they want to be confident in the quality. This means producers need to check for defects. The customer may reject them if there are too many as it can result in a serious risk of failure.

When you consider the bond line, in itself it is not actually a defect. It is simply heterogeneity in the metal in the weld area. You can even use the uniformity, shape, and orientation to get a better idea of the overall weld quality. However, you can often find discontinuities in the same area.

Come to us for quality ERW tubes

At Union Steel Tubes we have very high standards. In fact, we are ISO 9001 registered and have quality management present in everything we do. That includes in the equipment we use as well as the checks in place to make sure every product is suitable for use. As a result, clients can buy from us with complete confidence.

If you want ERW tubes for a project, come to us. We have a massive selection of sizes, both in terms of wall thickness and diameter. Plus, we can cut the tubing to specific lengths for you. Get in touch if you need any help.