Weld Inspection & AWS Visual Inspection (VT)

Visual testing (VT) is the first and most common way to check a weld. It needs only good light, a few gauges and a trained eye, and it catches most surface problems before they turn into expensive repairs. Welders use it on their own work, and inspectors use it to accept or reject work under a code. Limits quoted here come from AWS D1.1 for steel structures, and other codes differ.

What You Will Be Able to Do

• Separate an indication, a discontinuity and a defect.
• Choose and use the right gauge for each measurement.
• Inspect at each stage of the job.
• Apply D1.1 visual limits.
• Decide when a weld needs a different test.

Three Words That Matter

Inspection means moving through those steps in order. You notice an indication, decide if it is a discontinuity, measure it, and then compare it to the code. Only then do you call it a defect. Calling something a defect before you have measured it is a good way to lose trust on a job.

The Inspection Kit

An inspector carries a flashlight even in a bright shop. Overhead light flattens the surface. A beam held at a grazing angle makes shadows, so undercut, overlap and fine cracks stand out.

Inspecting at Each Stage

Inspection is not a single event at the end. Most costly problems can be seen before the final pass.

Before welding:

• WPS is at the station, and it fits the job.
• Welder's qualification is current and covers the work.
• Base metal and filler are correct, including paperwork such as mill test reports.
• Joint is clean, with bevel, land and root opening in tolerance.
• Preheat has been reached. Check it with a temperature crayon or an infrared gun.

During welding:

• Amps, volts and travel speed are inside the WPS.
• Interpass temperature is within limits.
• Each pass is cleaned before the next.
• Back gouging, backing or purge is done if required.

After welding:

• Final visual inspection and dimensions
• Any required heat treatment records
• Any required NDT
• Records completed and signed

How to Look at a Weld

1. Let it cool, and clean it. Remove slag and spatter so that nothing is hidden. Do not grind before inspection unless the procedure says so.
2. Get close and use good light. Common guidance is to keep your eye within about 24 inches, at an angle of at least 30 degrees to the surface.
3. Walk the whole weld. Check both toes and the face from end to end.
4. Use the flashlight at a low angle. Move it along the weld and watch for shadows.
5. Measure anything you are unsure of. Do not guess.
6. Mark it. Mark indications so that a repair crew can find them.
7. Write it down. Note the location, size, type and the governing code.

Measuring Common Features

Fillet Size

Choose the gauge for the specified leg size, and hold it against the weld and the base metal. On a convex fillet, the gauge should touch the plate and the toe with the weld fitting within the blade. On a concave fillet, use the side made for concave welds, which measures throat. Measure both legs. Unequal legs are common, and the smaller leg decides the size.

Undercut

Set the pointer of an undercut gauge against the plate and drop it into the deepest part of the groove. Hold it perpendicular to the toe, and read the depth. Do not estimate undercut by eye. The difference between 1/32 inch and 1/16 inch is too small to see reliably.

Reinforcement

Set the gauge on the plate and read how high the crown stands above it. Check at several points.

Misalignment

Set the gauge across the joint and read the step between the two sides. On pipe, use a hi-lo gauge on the inside.

AWS D1.1 Visual Limits

Current limits are in Table 8.1 of recent editions. Older editions list the same topics under different numbers, so always use the edition named in the contract. This is a summary and is not a substitute for the table.

Undercut Limits

Porosity Limits

Porosity limits depend on the weld type and its direction to the load.

• CJP groove welds in butt joints across tension: no visible piping porosity.
• Other groove welds and fillet welds: the sum of visible pores 1/32 inch or larger must not exceed 3/8 inch in any 1 inch of weld or 3/4 inch in any 12 inches.
• Fillet welds: the frequency limit is one pore in each 4 inches of length, at a maximum diameter of 3/32 inch.

Cyclic work has tighter rules, so read the correct column.

Reinforcement Limits

The limit depends on the thickness. On plate up to 1 inch thick, a common D1.1 limit is 1/8 inch, with more allowed on thicker plate.

Arc Strikes

Arc strikes on the base metal outside the weld are a problem on structural steel, because the fast cooling can leave a hard spot that cracks. They must be ground smooth and checked to confirm there is no crack.

Slag and Incomplete Penetration

All visible surface slag must be removed. On a CJP weld, incomplete penetration is a rejectable defect.

If the code says a crack is rejected, the weld does not get a discussion. It gets removed and rewelded, or the part is scrapped.

What VT Cannot See

VT can see only the surface. It catches surface cracks, porosity, undercut, overlap, wrong size and profile problems. It cannot see a flaw inside the weld. Subsurface slag, for example, will only be found by radiographic or ultrasonic testing, and the governing code then decides whether to accept it.

You move past VT when the code or contract documents call for it, or when something you see needs a closer look.

NDT needs qualified technicians. Your job as a VT inspector is to know which method fits the question, and to arrange it, not to run it without training.

Writing It Up

A good report can be understood by someone who has never seen the weld.

• Job, drawing and joint or weld number
• Governing code and edition
• Welder ID, if your system tracks it
• What you found, where it is and how big it is
• Accepted or rejected, and the clause or table
• Your name, date and signature

Rejected welds go to repair under an approved procedure. The repaired weld gets inspected again, as if it were new. Report what you see. An inspector's value depends on being honest, even when a schedule is at stake.

Inspector Credentials

The American Welding Society (AWS) runs the main US inspector program under its QC1 standard.

The CWI exam has three parts:

• Part A, Fundamentals: welding processes, metallurgy, testing, safety and symbols
• Part B, Practical: hands-on measurement and judgment on weld replicas
• Part C, Code: open book, in a code you elect, usually AWS D1.1

Experience requirements depend on your education, so check QC1 for the current rule. A high school diploma plus about 5 years of relevant experience is a common path. You also need a vision test. Certification is renewed every 3 years, and every 9 years you must recertify. Reading this guide does not qualify you to sign inspection reports.

Common Mistakes

• Judging by eye. Measure anything close to a limit.
• Using the wrong edition. Limits and table numbers can change.
• Grinding a flaw away before it is measured. You lose the record, and maybe the evidence.
• Reporting "bad weld." Give the location, size and reason.
• Skipping the pre-weld checks. A bad fit is harder to fix after welding.

Check Your Understanding

You see a thin line near a toe, but overhead lighting makes it hard to read. What do you do first?

Hold a flashlight at a grazing angle and clean the area. If it still looks like a crack and you cannot be sure, use PT or MT to confirm it.

A static fillet on 1/2 inch plate has undercut measured at 0.025 inch. Is it acceptable under D1.1?

Yes, for a static structure, since the limit is 1/32 inch (about 0.031 inch) on material under 1 inch. On a cyclic primary member loaded across the weld, it would be over the 0.010 inch limit.

You are asked to check a stainless weld for tight surface cracks. Which method do you choose, and why not MT?

Use PT. Most stainless steels are not magnetic, so MT will not work.

A weld passed VT, but the job also requires a check for internal lack of fusion. What happens next?

UT or RT, as the code or contract requires. VT cannot see internal flaws.

Key Takeaways

• An indication is what you see, and a defect is what the code rejects.
• Measure with the right gauge, and use a flashlight at a low angle.
• Inspect before, during and after welding.
• Use the D1.1 edition named by the contract. Cracks are always rejected.
• VT sees only the surface, so match PT, MT, UT or RT to the question.
• A report needs location, size, code and result.