Weld symbol
Complete joint penetration (CJP) symbol
CJP in the tail says the weld must fuse through the entire thickness of the joint. The preparation is left to the fabricator, so no groove size appears to the left of the symbol.
Reads asArrow side: V-groove weld, 60° groove angle, 1/8 root opening.
How to read it
A complete joint penetration callout is a statement about the result, not about the preparation. It says the finished weld must be fused through the full thickness of the parts being joined, with no unfused land, no unfilled root, and no gap anywhere across the section. How the fabricator achieves that is left open on purpose.
That is why the size to the left of the groove symbol is normally absent on a CJP callout. Writing a depth would over-specify the joint: the required depth is simply the material thickness, and stating it invites a mismatch when the plate is not the nominal size. The letters in the tail carry the requirement instead, and the groove symbol shows what shape of preparation is intended.
Achieving full penetration always demands access to the root, one way or another. Common routes are a double-sided preparation welded from both faces, a single-sided groove welded onto backing, or a single-sided groove followed by gouging and back welding. The symbol will usually show which of those is intended through the second symbol on the reference line.
CJP joints carry inspection consequences. Because the requirement is about the whole cross section and not just the surface, these are the joints most likely to be examined volumetrically with radiography or ultrasonics. Seeing the letters in the tail is a good early signal that the joint will be looked at through its thickness, not just along its face.
Where each dimension goes
- Tail note
- Carries the complete-penetration requirement itself. The letters in the tail are the instruction, not a size.
- Absent size to the left
- Deliberate. The required depth is the full thickness, so writing a number would only create a conflict.
- Groove symbol shape
- Shows what preparation is intended - vee, bevel, U, or J - without committing to a fill depth.
- Second symbol on the line
- A back weld, backing weld, or opposite preparation showing how root access will be achieved.
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: CJP achieved from both sides
TitleCJP achieved from both sidesRefCJP groove weldEx1 / 2Reads as
Prepare and weld this joint from both faces to achieve complete penetration.
Which mark says so
- V-groove symbolBelow the reference lineA V-groove weld on the arrow side of the joint
- 60°Beyond the outer face of the arrow-side symbolIncluded angle the joint is prepared to
- 1/8Inside the arrow-side symbolRoot opening - the gap left between the members before welding
- V-groove symbolAbove the reference lineA V-groove weld on the far side of the joint
- 60°Beyond the outer face of the other-side symbolIncluded angle the joint is prepared to
- CJPIn the tailA reference the drawing carries - a process, procedure or specification
Vee symbols above and below the line show a double preparation and the tail states the penetration requirement. No depth appears because the required depth is the whole thickness.
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.
Example 2: CJP from one side onto backing
TitleCJP from one side onto backingRefCJP groove weldEx2 / 2Reads as
Achieve complete penetration from the arrow side using backing at the root.
Which mark says so
- V-groove symbolBelow the reference lineA V-groove weld on the arrow side of the joint
- 45°Beyond the outer face of the arrow-side symbolIncluded angle the joint is prepared to
- 1/4Inside the arrow-side symbolRoot opening - the gap left between the members before welding
- backing symbolAbove the reference lineA backing weld on the far side of the joint
- CJPIn the tailA reference the drawing carries - a process, procedure or specification
The backing indication opposite the groove shows how the root will be supported, and the tail states that the finished weld still has to fuse through the whole section.
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
- Adding a groove size to the left of a complete-penetration symbol and creating a conflict with the plate thickness.
- Assuming complete penetration can be achieved from one side with no backing and no back weld.
- Reading the absence of a size as an incomplete symbol rather than as the point of the callout.
- Overlooking that these joints are the ones most likely to be examined through their thickness.