Which Plate Thickness needs to be beveled for Welding?

There are different reasons to bevel plate for welding and different types of bevel geometry depending on the thickness of plate to be welded. Generally, we would consider beveling plate thicknesses of 6 mm and above to enable the welder to reach and penetrate the root of the plates to be welded.

However, we also can bevel thin materials to deposit a flusher weld bead. An example of this is on hand railings so that the deposited weld bead can be flush with the tubing and therefore there would be no need to grind the weld bead after welding.

Let’s look at the types of beveling and the reasons we perform this preparation of the weld joint.

Basically, when we weld thin materials up to 6mm, the edges of the two plates are left square and this type of joint is called a butt joint, leaving the edges of the plates as per Figure 1.

Figure 1, Image of a butt joint showing a square groove edge geometry

One of the main reasons to bevel the plate edges is to make room to position the welding electrode in the joint and thus penetrate to the root. When welding a square groove joint, as the plate thickness increases,  it becomes difficult to penetrate to the root of the plate to perform a complete joint penetration (CJP) groove weld from one side only. Therefore, for thicker plate, this type of joint is best suited for partial joint penetration (PJP) groove welds where the weld does not penetrate the full thickness of the joint, as shown below in Figure 2.

 

Figure 2, Images of a complete and partial penetrating groove welds

To penetrate deeper into the joint we can open up the distance between to two plates and this will allow the electrode to penetrate deeper but, if the root opening is larger than the diameter of the electrode this becomes virtually impossible to weld. Therefore, we need to bevel the plate or plates. The following are examples of the types of bevels used on plate to achieve penetration to the root of the joints.

The types of bevels are usually determined by an engineer during the design stage. The bevel groove is used when we only require having one half of the joint beveled to make it possible to get the electrode to the root of the joint, when the thickness of the plates is generally over 20mm the designer may choose to bevel from both sides of the joint depending on whether the design is for a  PJP or CJP groove welds, see Figure 3.

Figure 3, Images of a single and double bevel joint geometry

The next type of joint beveling is chosen when the designer requires both sides of the joint to be beveled which creates a single V-groove when cut on one side of the joint and a double V-groove when the plates are thicker. This is performed to both reduce the amount of heat generated, by reducing the number of pass’s, when welding from one side and, to control distortion from a multipass weld on thicker plate, see Figure 4.

Figure 4, Images of a single and double V-groove joint geometry

When we attempt to weld thicker plates over 25mm the designer may decide on a “J” type joint configuration again, to allow the welder to position the electrode into the root of the joint. Also, on thicker plates we can reduce overall heat input and reduce distortion of the materials being welded by moving from the “V” to a “J” prep as shown in Figure 5.

Figure 5, Images of a single and double "J" joint geometry

Finally, when we need to machine and prepare both plates on thicker materials the engineer will choose the “U” type joint preparation, see Figure 6. Once again, as we increase the thickness then we reduce the amount of weld metal required to fill while giving access to the root. This reduces distortion and joint completion time. Reducing the amount of weld metal also reduces the probability of in joint defects.

Figure 6, images of a single and double "U" joint geometry

Bill Eccles, VP PPC and Associates