Weld symbol
Flare V-groove weld symbol
Two outward-bowing curves mean the groove is formed by the natural radius of two rounded members set together — no cutting involved, since the parts themselves create the vee.
Reads as: Arrow side: flare-V-groove weld, 1/4 size, 3/16 effective throat.
How to read it
The flare-V symbol is drawn as two curves that bow away from each other, mirroring the joint it describes: two rounded surfaces placed together so their radii form a natural groove. Round bar to round bar, tube to tube, and the rolled edges of two formed sections all produce this shape. Nothing is machined; the groove is a consequence of the parts' own geometry.
Because there is no cut, there is no groove angle to specify and no root face to dimension. What matters instead is how much of the naturally formed groove is actually filled. That is why flare grooves are dimensioned by depth and effective throat rather than by angle: the drawing tells you how deep the joint is filled and, where it differs, what throat that fill is credited with.
Two numbers to the left of the symbol are common on flare grooves. The first is the depth of the groove filled, measured from the face down into the flare. The second, in parentheses, is the effective throat — the dimension the joint is designed around. The throat is usually smaller than the depth because the curved faces mean the weld is thinner near the root than a straight-sided groove of the same depth would be.
Filling a flare groove completely is harder than it looks. The groove narrows toward the root and the curved faces reflect the arc, so incomplete fusion along the tangent lines is the characteristic problem. Inspectors reading this symbol usually pay particular attention to whether the weld actually reaches the effective throat the drawing credits it with.
Where each dimension goes
- Depth of fill (left of the symbol)
- How far into the naturally formed groove the weld metal reaches, measured from the face inward.
- Effective throat (in parentheses)
- The throat dimension the joint is designed around, usually smaller than the depth because of the curved faces.
- Length and pitch (right of the symbol)
- Run length and centre-to-centre spacing where the flare groove is welded intermittently.
- Side of the reference line
- Which face of the assembly the flare groove is welded from. Both faces can be called out.
Worked examples
Flare-V with depth and throat both stated
“Fill the flare groove 3/8 deep and credit it with a 1/4 effective throat.”
The first number left of the symbol is how deep the weld metal goes into the natural groove and the parenthesised number is the throat the design relies on, which is smaller.
Flare-V welded from both sides
“Weld the flare groove from both faces, 1/4 deep on each side.”
A curved symbol above and below the reference line means the assembly is welded from each face, with each side carrying its own depth into the naturally formed groove.
Common mistakes
- Looking for a groove angle on a flare symbol. There is none, because nothing is cut.
- Reading the parenthesised throat as a second depth rather than as the credited weld throat.
- Assuming a flare groove filled level with the face has developed the full throat. The curved root often is not fused.
- Confusing a flare-V with a flare bevel, which has one straight member instead of two curved ones.
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.