Weld symbol
Field weld symbol
A flag at the elbow says the weld is made in the field rather than in the shop. It is a scheduling and quality instruction, not a change to the weld itself.
Reads as: Arrow side: fillet weld, 5/16 size.
How to read it
The field weld flag is drawn at the elbow, flying from the leader where it meets the reference line. Like the all-around circle it modifies the entire reference line rather than any single weld symbol, and it says one thing: this weld is not made in the shop. It is made wherever the assembly is finally erected or installed.
The flag changes nothing about the weld's size, type, or dimensions. A 5/16 fillet with a flag is the same weld as a 5/16 fillet without one. What changes is everything around the weld: the position it has to be made in, the access, the weather, the power available, the process that is practical, and how the weld will be inspected once it is up in the air or in a trench.
For the shop, the flag is a boundary marker. Everything without a flag is fabricated before the assembly ships, and everything with one is deliberately left open so the pieces can be transported and fitted. Welding a flagged joint early can make an assembly too large to move or lock in dimensions that need to float until erection.
For inspection, the flag is a warning. Field conditions make preheat harder to hold, expose low-hydrogen consumables to moisture, and put welders in positions they would never choose in the shop. Joints carrying this flag deserve a closer look at the conditions surrounding the weld, not just at the weld itself.
Where each dimension goes
- Flag at the elbow
- Says the weld is made away from the shop. It applies to the whole reference line, not to one symbol.
- Flag orientation
- It flies from the leader at the reference line junction, conventionally pointing back toward the tail end.
- Effect on weld dimensions
- None. Size, type, length, and contour read exactly as they would on a shop weld.
- Combination with the all-around circle
- Both can occupy the elbow together and each keeps its own separate meaning.
Worked examples
Field-welded erection splice
“Make this 3/8 fillet on site during erection, not in the shop.”
The flag at the elbow marks the whole reference line as field work. The 3/8 size is unchanged by the flag; only where and under what conditions the weld is made changes.
Field-welded groove with a procedure reference
“Weld this groove in the field using the procedure named in the tail.”
The flag says the joint is made on site and the tail carries the procedure, which matters more in the field where preheat and consumable control are harder to maintain.
Common mistakes
- Welding a flagged joint in the shop, which can leave the assembly too large to transport or over-constrain the fit at erection.
- Reading the flag as a change to the weld's size or type. It changes only where the weld is made.
- Applying the flag to one weld symbol when it governs the entire reference line.
- Treating field welds as ordinary shop welds at inspection despite the harder conditions around them.
Typical joints
Related symbols
Practise reading welds, not just symbols
The drawing tells you what the weld should be. The gauge trainer is where you find out whether you can tell what it actually is.