Weld Joints and Positions

Welders, fitters, inspectors and engineers all use the same short words to describe a weld: lap joint, fillet weld, 3G. If you know these words, you can read a work order, follow a print and understand what a test covers. They are the same for every arc welding process.

What You Will Be Able to Do

• Name the five basic joint types.
• Tell the difference between a joint and a weld.
• Name the parts of a fillet weld and a groove weld.
• Read a position code such as 2F, 3G, 5G or 6G.
• Explain why position changes how you weld.

Joints and Welds Are Different Things

A joint is how two pieces of metal meet. A weld is the metal you put there. The same T-joint might get a fillet weld or a groove weld, depending on how strong it has to be. Keep these two ideas separate and prints start making sense.

The Five Basic Joints

Fillet Welds and Groove Welds

Most welds you make will be one of two types.

Fillet Welds

A fillet weld fills the corner between two surfaces, and its cross section is roughly a triangle. Tee, lap and corner joints usually get fillets. They need little or no edge prep, so they are the most common welds in fabrication.

The parts of a fillet weld:

• Leg: The distance from the root of the joint to the toe, along each piece. Fillet size is normally given as the leg length.
• Root: The inside corner where the two pieces meet.
• Toe: The line where the weld face meets the base metal.
• Face: The exposed surface of the weld.
• Throat: The shortest distance from the root to the face. It carries the load.

Groove Welds

A groove weld is made in a gap or prepared opening between two pieces. Butt joints usually get groove welds. Thicker metal is usually beveled, which means an edge is cut at an angle, so the weld can reach the full depth.

The parts of a groove:

• Bevel angle: The angle cut on one piece.
• Groove angle: The total angle between the two pieces, also called the included angle.
• Root face or land: The small flat left at the bottom of the bevel.
• Root opening or gap: The space between the pieces at the root.
• Reinforcement: Weld metal above the surface of the plate, also called the crown.

Complete joint penetration (CJP) means the weld goes all the way through the joint. Partial joint penetration (PJP) means it goes only part of the way, to a depth the print specifies.

Reading Position Codes

A position code has a number and a letter. The number gives the position. The letter gives the weld type: F for fillet and G for groove. So 2F is a horizontal fillet weld and 3G is a vertical groove weld.

Each position changes how you weld.

• Flat: The easiest. You can use the highest current and the fastest deposit rate.
• Horizontal: On a fillet, aim more at the bottom plate so the bead does not sag. On a groove, use small stringer beads.
• Vertical: Use lower heat than flat. Welding uphill gives deeper penetration and is usually what structural work calls for. Welding downhill is faster and shallower, and is used on thin metal and some pipeline passes. Only weld downhill if the procedure allows it.
• Overhead: Use a small puddle, a short arc and lower heat. Wear full leathers, because spatter falls on you.

Pipe Positions

Pipe uses the same idea, but the code tells you how the pipe sits and whether it can turn.

A code with an R, such as 6GR, adds a restriction ring placed near the joint so the welder has limited access. A test like that simulates welding in a tight spot.

Pipe fillets use codes such as 1F, 2F, 2FR, 4F and 5F. In these, a letter R means the pipe is rotated. The R in 2FR means rotated, while the R in 6GR means restricted. The code body's figures define each one.

Why Position Codes Matter

You will see these codes in three places:

• On a print or work order, where they tell you what is coming.
• On a welding procedure, where the procedure lists the positions it allows.
• On a welder qualification, where they list what you are tested and allowed to weld.

The positions you are qualified for after passing a test depend on the code that governs the work. As a rule, a harder test covers more positions. The details differ between codes, so always check the governing code and do not assume.

Worked Example: Reading a Job

A work order says: "Weld 1/4 inch fillet, 2F, on the tee joint at each stiffener."

1. Joint: Tee. A stiffener stands square to the plate.
2. Weld type: Fillet. The letter F agrees with this.
3. Size: 1/4 inch leg.
4. Position: Horizontal. The plate is flat and the stiffener stands up, and you weld along the corner.
5. What you do: Aim the arc slightly more at the flat plate, so that the weld does not sag and both legs come out equal.

Now change one detail to 3F. The stiffener line now runs up a vertical wall, so you turn the heat down and weld uphill, unless the procedure says otherwise.

Common Mistakes

• Mixing up joint and weld. Saying "fillet joint" confuses a print reading. It is a tee joint with a fillet weld.
• Reading 1G on pipe as flat plate. On pipe, 1G means the pipe rolls under you.
• Assuming that 2G means the same on plate and pipe. On pipe, the pipe stands vertical and the weld runs around it.
• Sizing a fillet by looks. Use a gauge. An undersized fillet can fail inspection, and an oversized one wastes metal and adds distortion.
• Assuming a test covers everything. Your coverage is limited by the code and the test you took.

Check Your Understanding

Two plates sit edge to edge, and the drawing calls for a weld through the full thickness. What are the joint and the weld?

It is a butt joint with a CJP groove weld.

A plate is mounted on a wall and you need to run a groove weld straight up it. What is the position code?

3G. The 3 means vertical and the G means groove.

A pipe is fixed in a horizontal rack and cannot be turned. What is the position, and what does it mean for your work?

It is 5G. You work around the joint and pass through flat, vertical and overhead, adjusting as you go.

On a fillet weld, which measurement carries the load: the leg, the toe or the throat?

The throat. The leg is what you normally measure and what the print calls for, but the throat is the shortest path through the weld.

Key Takeaways

• A joint is how the metal meets, and a weld is what you put there.
• The five joints are butt, tee, lap, corner and edge.
• F means fillet and G means groove. The numbers 1, 2, 3 and 4 mean flat, horizontal, vertical and overhead.
• Pipe 1G rolls, 2G stands vertical, 5G is fixed horizontal, and 6G is fixed at 45 degrees.
• Position changes your heat, your angle and your speed.
• What a test qualifies you for depends on the governing code.