When making welds, the size and thickness of the weld are significant factors that contribute to its strength. Since one feature of a good weld is that the strength matches the application, it is crucial to understand weld sizes. What is the maximum weld size?
The maximum size of a fillet weld typically corresponds to the thickness of the thinner of the two materials being joined. However, very large welds may cause extremely high residual stresses and unacceptable distortion, so pay attention to the limits.
This article describes the throat thickness of a weld and what the maximum weld size is. I also explore whether you can weld multiple passes and the types of weld joints you can make.
What Is the Throat Thickness of a Weld?
The throat thickness of a weld primarily refers to a fillet weld. Typically, it should at least be as thick as the thickness of the metal you are working with, and it can also be any size the designer specifies.
Fillet welding is a process that joins two pieces of metals at an angle or when they are perpendicular. One aspect of a fillet weld is the throat and its thickness factors into the strength and stability of the weld joint.
The loads a fillet weld is expected to carry will determine the throat thickness. Even though butt welds have a throat, the throat aspect is more significant in fillet welds, and the two types of fillet throat are:
- The actual throat
It is the distance from the center of its face to the root. It also describes the shortest distance minus any reinforcement between the root and the face.
- The theoretical throat
It is a dimension based on the assumption that the root opening equals zero. This is the minimum distance from the beginning of the joint root perpendicular to the hypotenuse of the largest right triangle that can be inscribed within a filet weld cross-section.
What Is the Maximum Weld Size?
A filet weld must be sizable enough to carry the applied load, but its specified size should not be excessive to minimize distortion and costs.
Sometimes, the weld size on the drawing might be unclear, not reported, or the information is missing. You should contact the designer to fill in the blanks in such scenarios.
The maximum size of a filet weld will be equal to 0.7 x T, where T is the base metal thickness. Consider the thinner base metal thickness with different thicknesses. You can also get it by subtracting 1.5 mm from the thickness of the thinner member to be joined.
This maximum size should not exceed 3/4 of the welds’ section’s thickness at the toe. Above a certain weld size, it may be more economical to make a T-butt weld.
Can You Weld Multiple Passes?
The multi-pass welding technique is an acceptable procedure that allows you to weld joints of varying thicknesses for base metals of different grades. In multi-pass welding, you apply multiple beads or passes to increase your weld area.
Depending on the application of the weld, an increased area increases the strength of the joint. Welding multiple passes also allows for temperature monitoring to reduce hot/cold cracking or peening for stress relief.
You deposit another pass over the first one after it has cooled down, and you keep doing until you have the thickness you want. Ensure to clean off all the slag from one pass before depositing another pass.
Applications and Benefits
- Multi-pass welding is used to join thick sections
- When the specified filler will not produce the correct root depth and bead size, you use multi-pass welding.
- It is also convenient for creating large weld beads while maintaining a minimum level of heat input. The time between creating beads allows the temperature to reduce before adding a new bead.
- Certain base metals also require the multi-pass welding technique.
- Using this method for thick materials eliminates welding defects that arise from overheating and not giving enough time for the contaminates to float out of the thicker welds.
- Large steel pipes and thick steel plates on ships use this welding technique.
In summary, the benefits of a multi-pass weld include a good evenly sized bead appearance, welding of higher thicknesses, increased joint strength, and tempering of the heat-affected zone (HAZ) of the previously deposited weld successfully.
How Many Types of Weld Joints Can You Make?
Welding is a craft that requires creativity and an eye for detail. To deliver quality welds, you must have a solid understanding of the practices, techniques, and terminologies used in the industry, including the types of joints.
The five major types all meet the forces and needs of specific applications, and I outline a brief description of each joint type below:
- Butt joint
You make a butt joint by placing two metal pieces together in the same plane and joining them. It is the most common joint found in piping systems and the fabrication of structures.
This joint requires a weld prep to give it enough strength, and the bigger the prep, the stronger the joint. Examples include the square, single J, double V, and double bevel joints.
- Tee joint
Placing and joining two metal pieces at a 90° angle creates a tee joint. The edges meet in the center of a plate in a ‘T’ shape, and some styles you can use to make this joint include J-groove weld, fillet weld, spot weld, etc.
- Corner joints are similar to tee welding joints, differing only in the positioning of the metal. The metal pieces of a corner joint meet to form an ‘L’ shape in the plate’s corner or component.
- Edge joint
To form this joint, you place the metal surfaces together, with the edges even. It always has one butt weld on it, but it can also have the other three sides welded with butt or fillet welds.
- Lap joint
One plate overlaps another, creating two sections for fillet welds—one above and one underneath. They are a modified version of the butt joint and are easy to weld.
Each joint design affects the cost and quality of the weld, so selecting the most suitable one per project is essential.