Visual weld inspection: before, during and after

Why three stages beat one final look

A finished weld only shows its surface. A bad joint fit, the wrong consumable, a skipped cleaning step or a missed preheat can all be hidden by the last pass. An inspector who only looks at the end sees the symptoms. One who looks at all three stages catches the causes. It's also how inspection is organized on most jobs: hold points before welding starts, checks as it proceeds and a final review before the weld goes to NDE or acceptance.

Stage 1: before welding

You're checking that the job is set up to succeed.

• Documents. Confirm the drawing, the welding procedure and the welder's qualification record all apply to this joint, material and position. Why those records matter is covered in WPS, PQR and WPQ explained.
• Materials. Check that base metal and filler match the documents, are identified and are in good condition. Consumables that need dry storage should have been kept that way.
• Joint preparation. Look at the bevel, root opening, root face and the cleanliness of the surfaces. Rust, oil, paint and moisture near the joint cause porosity and other flaws.
• Fit-up. Check alignment, gap and tack welds. Misalignment and an uneven root opening are far easier to fix before welding.
• Setup. Confirm that any preheat required by the procedure is in place, with the right measuring tools on hand, and that the welder has what the procedure calls for, such as correct shielding gas.

Stage 2: during welding

Here you verify that the procedure is actually being followed.

• Variables. Compare what you see (process, electrode or wire, travel direction, technique) with the procedure. Preheat and interpass temperature need checking at intervals.
• The root pass. It's the hardest to see once covered. Look for fusion and penetration before the next pass buries it.
• Between passes. Check that slag and spatter have been removed and the previous bead has no defects that will carry into the next layer. A crack found at pass two is a short repair. Found at the last pass, it's a long one.
• Protection. In gas-shielded processes, watch for drafts and gas flow trouble, which cause porosity.
• Repairs. Where a flaw is removed, confirm that it's fully gone and the area is prepared again before rewelding.

Stage 3: after welding

Now you judge the finished weld. Do it in a fixed order so nothing is skipped:

1. Cleanliness. The weld must be clean enough to see: slag, spatter and scale removed as the job requires.
2. Discontinuities. Look for cracks, lack of fusion, undercut, overlap, porosity, incomplete fill and arc strikes. Weld discontinuities explained shows what each one looks like and why it forms.
3. Dimensions. Measure size, reinforcement, length and any other quantity the drawing or specification calls for.
4. Profile and appearance. A smooth transition at the toes and a consistent bead matter for fatigue and for the next examination.
5. Marking and records. Confirm identification, welder marks where required, and that the paperwork matches the work.

Record what you measured and saw first, then compare it with the governing acceptance criteria. Keep observation and decision separate. On D1.1 work, D1.1 visual acceptance criteria, explained shows where those criteria sit and how static and cyclic connections differ.

A useful habit is to write one line per stage in your notes: what you checked, what you saw and what you'd do differently. After a few welds the pattern of where problems start becomes obvious, and so does where to look first.

Tools and lighting

Visual inspection needs more than good eyes. Make sure you have adequate light, a clear line of sight to the weld and the tools for the dimension you need: a gauge, a ruler or tape, a flashlight and a mirror for hard-to-see areas. Know which tool measures which feature. A gauge built for one weld feature can't be assumed to read another. The Part B measurement workflow covers how to name the quantity, take the reading and move to the criterion.

From routine to Part B practice

Part B is hands-on and open book, with 46 questions in 120 minutes, so there's time to look carefully but not to repeat every reading. The stages above give you the order of looking. The Part B guide lists what you get at the table and where the points are. For measurement practice, the weld gauge trainer lets you take readings on drawn welds.

Try this: pick any welded item you can see, such as a trailer hitch or a handrail, and run the three stages in order. Note what you could check, and what you would have needed to see earlier. If you want to see which Part B skills to drill first, the free 10-question Part B check is scored by area and shows exactly which topics to study first. Take it here.

FAQ

What does a visual inspector look for on a finished weld?

Surface discontinuities such as cracks, undercut, overlap, porosity and incomplete fill, plus dimensions like size and reinforcement, profile, cleanliness and markings. Acceptance limits come from the governing code or specification.

Is visual inspection really needed if there will be NDE?

Yes. Visual examination usually comes first, and it can reject a weld before money is spent on further methods. It also catches setup and process problems that NDE finds only after the fact.

When should preheat be checked?

Before welding starts, and again during welding as interpass temperature. The procedure sets the requirement, and the inspector verifies it with proper temperature tools.

What tools does a CWI carry for visual inspection?

Typically a weld gauge for the relevant features, a ruler or tape, a flashlight, a mirror, a magnifier and a temperature indicator. The exact kit depends on the work and the contract.