What are the Parts of a Weld? Explain with Diagram

When you begin to explore welding, you should familiarize yourself with the terminology, especially the parts of the weld itself.

Understanding these terminology not only facilitates communication on the job site, but it also enhances your ability to understand performance and evaluation of welds. If you have a diagram or picture of a weld, have it available it will help with these discussions.

Fillet Welds

Fillet welds are one of the most common kinds of welds in the industry. This type of weld is generally used for two metal pieces meeting at a right angle or at angles between roughly (60° and 120°).

The most common terms used in fillet welding are T-joint (two pieces jointed together perpendicularly) and lap joint (one piece overlaps another and the weld runs along the edge of the overlapping piece).

The weld bead formed above is in the shape of a triangle. Depending on how the welder is performing the fillet weld, the surface could be concave, flat or convex. Each shape can have an effect on the strength and aesthetic.

Fillet welds are useful and effective. You can see them a lot when flanges are welded onto pipes or when welds need to connect cross sections. They are also useful when; for example, bolts cannot take on the load or if they will wear out after time.

Groove Welds (aka Butt Welds)

In comparison, groove welds (butt welds) are used to join/attach two pieces of metal when the pieces are arranged equally on the plane of each part and touching only edge to edge without overlapping at all.

Groove welds are not like lap joints (one part on top of another) or plug welds (one piece inscribed into to the other), they join parts along the seam created when two pieces are brought together in a straight line.

For butt welds to be effective, it is important that both surfaces are both level and flat, and the filler material resides within each surface plane, to provide a sound clean weld, with no excess material beyond the planes of the two pieces, or less strength to the joined part of the structure.

Parts Of a Weld Explained

Before proceeding with any welding operation, welders must understand common welding terms.

Base Metal: The fundamental material you are welding, the one you’re welding to. Typically, this constitutes the main part of any weld.

Electrode: The electrode delivers electrical current to the weld area. Depending on the method of welding you are using, you can have melting electrodes (consumable) or non melting electrodes (non-consumable). In shielded metal arc welding, electrodes are coated in a special flux to protect the weld from contaminants.

Weld Bead; The weld bead is the raised strip of metal you see after a single pass with the welding torch along a weld joint.

Weld Pass: A weld pass is defined as each time you use the torch to move along a seam and deposit material. A single pass is a weld that only has a single pass. The thicker the joint, the more multiple passes of weld material are placed on top of each other. The heat source is moved in a rippling motion, causing the ridges in the weld bead.

Ripple: Ripples are the small waves or ridges left in the weld bead and they are similar to the temporary trail left when moving the welding torch.

Crater: At the end of a weld bead you can create a little depression or dip, which is referred to as a crater. The crater occurs as the torch moves away from the weld and the heat is released.Joint Penetration: This indicates the depth into the joint the weld has progressed, measured from the surface, down, and excludes any additional buildup of material above the joint.

Weld Reinforcement: There are times that extra weld metal is added on top of the required joint fill, this extra metal is called the reinforcement.

Root Reinforcement: This is reinforcement on the opposite side of the original weld application, basically the backing side.

Face Reinforcement: This is the reinforcment on the same side as the weld, or what you see when you look at the finished bead.

Root Face: The root face is the flat surface at the the bottom of the groove in a weld joint for the joint members occur closest together before welding.

Root Opening: This is the gap between the two pieces of metal at the bottom of the joint opening, before the start of the weld. It is important to get this right because a gap that is too wide or too tight is going to cause issues and require additional amounts of filler metal than is necessary.

Weld Width: Measured from toe to toe (we will discuss these next), this is the overall width across the surface of the weld.

Weld Toe: The weld toe is where the weld meets the base metal on either side of the weld. It is also where the weld stops and the original metal begins.Weld Face: After the welding process has happened the weld will have a weld face. The weld face is the part of the weld that you can see; it is affected by weld technique and can be concave or convex and is surrounded by the toes of the weld (which are described below).

Weld Leg: A fillet weld can be viewed as having two legs; the leg is the measurement from the toe of a weld to the root of the weld where the two pieces come in contact. The two legs form the geometry of the fillet.

Weld Root: The root of the weld is the deepest part of the weld, where the filler metal melted together with the base metals and penetrates into the joint the furthest.

Joint Root: The root of the joint is simply the point or area of point in relation to the two joint members in the closest place or area, before welding takes place.

Root Bead: The root bead is, specifically, the first weld bead that is laid and touches or goes into the root of the joint. So if you are performing a multi pass weld, the root bead will be the base for all of the pass layers.

Root Pass: The root pass is the first weld pass that achieves full penetration through the thickness of the joint; which is very important to the integrity of the weld!

Filler Metal: The filler metal is the metal that you are adding (or brazing or soldering) as part of the welding process to create a joint. Upon fusion with the base metal, while to unlimited or various strengthening to the joint depending on the filler metal used.

Fusion welding: Fusion welding is generally what people think of when they hear, “welding.” Fusion welding involves melting the base metals, and sometimes filler metal too and all pieces once they cool – are fused together as the cool. This is the primary welding process to combine any/all methods of jointing.

Fusion Zone: The fusion zone is the area of the metal that actually melted when the fusion welding process was completed. Remember that there is also a heat affected zone (HAZ) of the metal that was heated but did not melt. The goal is to fused areas of melted metal together securely solder or weld.

Fillet Weld Throat: When we reference the throat of a weld, we are almost always going to reference either: 1) Actual Throat 2) Theoretical Throat

• Actual throat: The Actual Throat is the shortest distance from the faces of a fillet weld to the root after welding.
• Effective throat: The Effective Throat is the minimum distance from the root to the face of the weld minus any reinforcement.
• Theoretical Throat: The Theoretical Throat is the distance in the cross-section of a fillet weld, from the start of the joint root, perpendicular to the hypotenuse of the largest right triangle that can be inscribed, based on the assumption that the root opening is equal to 0.

What Is the Size of The Weld?

• Equal Leg Length Fillet Welds: When the two legs of a fillet weld are of the same length, we refer to this as an equal leg fillet weld, Figure 4.2. The size of this type of fillet weld is determined by the leg length of the largest right angled isosceles triangle that can be inscribed into the weld. For reference, the theoretical throat the shortest distance from the root of the weld to the face is 0.7 times the size of the weld.
• Unequal Leg Length Fillet Welds: Now, in the case of fillet welds that feature two legs of unequal length (which is quite common in practical situations) the size of a fillet weld is determined differently, When an unequal leg length fillet weld is being sized we are valuing the weld based on the shortest leg of the largest right triangle that can fit inside the fought cross section of a transverse section on the weld. This way of sizing provides consistent safety factors without overvaluing the effective strength of the weld.

Multi-pass Welds: Heat Affected Zones in The Parts of A Weld.

In instances of welding or in welding joint preparation where if you have complex joints welds; it is common to run a multi pass weld.

This is very straightforward and just means that one weld bead isn’t enough to fill the joint required, requiring multiple passes until the weldment accumulates enough layers to join the base metals confidently.

Now any time you are butt welding and using multiple passes such as mentioned above, you are creating what are called heat affected zones (HAZ) in the process. The first pass creates the primary heat zone and the base metal that has been affected during the first application of heat and filler metal.

Now the second pass you will create a secondary heat zone, which overlaps the first, during the second pass we are applying additional heat to the first pass.

An interesting fact in this process is, the heat from the second pass not only melts the new fill metal but actually improves the properties of the first pass.

In this process the heat from the second pass provides what we call annealing in the primary zone or the first pass to soften the metal just enough to release some internal stresses and contribute to fusing the base metal effectively.

So, opposite what you may believe, the secondary heating from the second pass during welding only strengthens the original weld.

Not to mention the fact that the fill metal you applied in the first pass also benefited from this heat input during the second pass.

This heat input aids in refining the properties of the fill itself and the bonding of the filler to the joint; which overall can guarantee your welds maintain overall structure and performance.

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