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 asArrow 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
Each one is a drawing, the sentence it comes out as, and then the mark-by-mark account of why. Read the sheet first and say the sentence yourself before you look down.
Example 1: Flare-V with depth and throat both stated
TitleFlare-V with depth and throat both statedRefFlare V-grooveEx1 / 2Reads as
Fill the flare groove 3/8 deep and credit it with a 1/4 effective throat.
Which mark says so
- flare-V-groove symbolBelow the reference lineA flare-V-groove weld on the arrow side of the joint
- 3/8Left of the symbolGroove weld size - how deep the weld itself goes
- (1/4)Left of the symbol, in parenthesesEffective throat - the load-carrying dimension, not the leg
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.
And what it does not say
- No length is given, so each weld runs the full length of the joint.
- Nothing sits above the reference line, so the far face of the joint stays bare.
- There is no circle at the elbow, so the weld does not continue around the joint.
Example 2: Flare-V welded from both sides
TitleFlare-V welded from both sidesRefFlare V-grooveEx2 / 2Reads as
Weld the flare groove from both faces, 1/4 deep on each side.
Which mark says so
- flare-V-groove symbolBelow the reference lineA flare-V-groove weld on the arrow side of the joint
- 1/4Left of the arrow-side symbolGroove weld size - how deep the weld itself goes
- flare-V-groove symbolAbove the reference lineA flare-V-groove weld on the far side of the joint
- 1/4Left of the other-side symbolGroove weld size - how deep the weld itself goes
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.
And what it does not say
- No length is given, so each weld runs the full length of the joint.
- There is no circle at the elbow, so the weld does not continue around the joint.
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.