Types Of Welding Joints Design and Welding Symbols
Types Of Welding Joints – Welding joint is an arrangement or configuration of the two pieces of metal (or more) that will be welded together. There are 5 basic joints that are most commonly known and applied according to American Welding Society (AWS) and many another standard. There is also any other type of joints which is actually derived from the 5 basic types of joints that are rarely mentioned in any textbook. Joint configuration is an important matter and highly essential on determining whether the welded joint can withstand the load that’s imposed on it, putting aside weld integrity factor.
In some extend an improper joint configuration can also compromise the integrity of the weld joint. An improper configuration of the joint can cause weld and material defect, for example, incomplete penetration, cracking, lamination, etc. Thus an extensive knowledge about how to configure a proper welding joint can tremendously help the engineering process so that it can minimize any potential failure of the weld joint. This article will try to break down all things that we know about welding joint.
TERMS IN WELDING JOINT
Before we talk about different welding joints we should understand the anatomy of a single joint. Figure 2 above should tell you the parts of a single joint (groove welded and fillet welded) that you need to know. While there are other variations of joint, the element that made a joint doesn’t vary that much. Several things that you should note for yourself when you’re welding or inspect a joint are its angle, its groove shape, its root, and its weld size.
Bevel angle or groove angle is varied depending on the required strength and metal thickness. Mostly the material is chamfered on the same angle each, so a bevel angle is half of the groove angle. It’s a little bit different in fillet weld, where mostly the joint is fixed to be perpendicular and is not commonly beveled. This makes measuring the angle of those two types of weld a little bit different. In fillet weld, the measurement is only based on the perpendicularity of the joint configuration while in butt weld the measurement can be done on each bevel or just the groove angle. Different measuring method may be needed when dealing with different groove shape. The earlier method is best when being used to measure the angle in bevel or V-shape groove, however, it doesn’t work for U or J-shape groove. For the later, the element measured is not the angle of the groove but instead the fillet radius of the groove.
Another important element is the root. Depending on the design, the joint could be open or closed joint. In open joint, there’s an opening between two base metals to allow the weld to melt through, this opening is called root opening or gap and its size is entirely based on the welder’s preference. A root face is the thickness of the root to prevent excessive penetration or melt through. The size is also entirely based on the preference of the welder.
The measurement of weld size is also different on either butt weld or fillet weld. It’s a little bit simpler on butt weld because the geometry is not that complicated, the measurement can be done parallel to the thickness plane of the base metal. While on fillet weld, it’s a little bit complicated. To simplify things, the measured element is like those of a triangle. The measurement is not just throat but also leg, which is non-existent in butt weld.
5 Welding Joint Types:
This type of joint is the most commonly used welding joint. It’s relatively easy to prepare and there are many variations that can be applied to manipulate the desired result. Those variations include the shape of the groove, the width of the gap, layer variation, and any other process. Basically, both metal in this joint is configured to align on the same plane and the side of each base metal will be joined by welding.
The shape of the groove is varied and engineered for the sake of joint strength. In thinner material, the groove is usually left unaltered, making the letter I shape, thus sometimes called “I” groove. Depending on the strength requirement, for lesser strength but faster welding, the joint is configured to be closed joint, meaning that there’s no gap where the weld metal can penetrate, when there’s gap between the parent metal it becomes open joint, allowing the molten weld metal to penetrate along the thickness and creating wider bond for greater strength. In thicker material, there are many options of groove shape. The single V and bevel are the most commonly used. Each of the weld faces is chamfered within a certain angle and together it makes the V shape. Other than V, there are also several another shape that’s commonly used, please refer to figure 3 below.
Butt joint is relatively easy to prepare and perhaps the only joint that’s suitable for automatic welding. Because there is a minimum obstruction on the weld path, so the automated device (e.g. SAW) can easily pass. This joint can be applied in any case, from plate to pipe, from the simplest rig platform to the most complex vessel wall.
The drawback of this joint is minimum. There’s no weld defect that’s exclusively caused by the use of butt joint. It makes this joint a must use whenever possible. The most commonly occurring weld defects are porosity, slag inclusion, incomplete penetration, burn through, cracking, and incomplete fusion all of which is independent of the joint design and can be easily averted by manipulating the welding variables.
Tee joint is a joint on which the base metal is perpendicularly configured to each other and the welding is done as fillet weld on one side or both side of the joint. Tee joint and any other fillet joints are not usually prepared with groove unless the base metal is thick and welding on both sides are not sufficient to withstand the load imposed on the joint. Though grooving is done like those of bevel, only one of the base metal is chamfered. Tee joint found its application in many components that are not possible to be weld except perpendicularly. Tee joint can be welded with almost all welding method with some complication found when welded (though still possible) with SAW (Submerged Arc Welding).
A defect that exclusively associated with tee joint is lamellar tearing (however, this defect is also common in any other fillet welded joint). Lamellar tearing occurs due to the high constraint experienced by the joint. Not allowing the joint to deform by placing stopper is a common practice among welder. While it’s effective to prevent and minimize deformation, the material is experiencing a lot of stress that build up in the weakest layer before it cracks or tears. It is important to only moderately constrain the joint because the process of welding will burden the material. Other types of defects that also may occur include porosity, slag inclusion, incomplete penetration, lack of fusion, and cracking. All of which can be manipulated by controlling the welding variable.
A modification of butt joint, where the material that resides on the same plane is configured to overlap each other and then fillet welded. However, there is also another welding method that can be applied to lap joint such as slot weld, plug weld, and spot weld. The application for this joint is mostly on sheet metal while it’s also rarely used on thicker material such as plates and pipe (socket weld). The base metal is not usually grooved when fillet welded. Though in another welding method such as slot and plug weld a special preparation is required to give some kind of pathway for welding.
There are several drawbacks in lap joint. For instance, the case of lamellar tearing also commonly occurs in thicker material whether it’s fillet welded or plug and slot welded. The problem of corrosion can also occur because of the wide contact area on which the material overlap.
Corner joint is very similar to tee joint, the difference is the location of the metal wherein tee joint it’s positioned rather far from the corner or simply said in the middle, but in corner joint the corner of both metals meets in either closed or open manner. It kind of looks like the corner of a box where the two perpendicular metal meet. That being said, the application of this joint is mostly on a metal box construction or any construction that resembles a box. The joint can only be fillet welded with any welding process that can reach the connection.
Types of defects associated with corner joint are lamellar tearing, incomplete penetration, porosity, slag inclusion, etc. similar with tee joint. To minimize the occurrence of these defects a little variation can be applied. Variations such as grooving the welded metal and using open corner joint instead of closed corner joint.
This one is similar with lap joint where parts of the base metal overlapping each other, but instead of fillet welded this joint is butt welded on the thickness side where the end of the material meets. This joint is also similar to flanged corner joint and flanged butt joint, where part of the base metal is bent and welded on the end side. Because there’s a contact area of the two metal, corrosion is a problem. So does defects like porosity, slag inclusion, and lack of fusion just like in any other type of joint.
Other Type Weld Joint
While there are probably many other joint configurations which are sometimes exclusive to some certain welding process or some product, making it not widely used. One type of special joint that’s familiar to me is cruciform. It’s basically two base metal perpendicular to one base metal forming a cross. This joint can be commonly found on ship bottom girder, the part that connects bottom center girder with bottom frame.
Joining this part can be complicated due to the built up stress that caused by the welding. Making it a stress concentration point that can severely weaken the connection. That’s why when designing a joint that forms a cross, a special testing method that determines the fatigue strength of the joint is compulsory because of potential failure. For Welding Symbols, see Welding Symbols Guide and Chart.