What this module covers
Part B is the practical exam: 46 questions in 120 minutes, on paper at an AWS test site. You measure plastic weld replicas with an inspection tool kit and answer questions from an exhibits booklet, with the Book of Specifications supplied for the exam open in front of you. The CWI Examination User Guide has candidates take Part B first, before Parts A and C.
Practical Applications: Welding Inspection and Discontinuities carries at least 40% of the Part B weight in AWS B5.1:2025 Table 8.1, more than any other area. Almost every one starts with a number you read off a gauge, and a wrong reading sinks the clause lookup that follows.
This module teaches the tools. Module 2 teaches how to judge the reading against the book.
The kit contents and the replica format here are our understanding from general practice. Check the CWI Part B Practical Exam Info (Rev. 03.01.2024) for what you will actually be given.
Fillet weld gauges and weld size
What the gauge set looks like
A leaf-type fillet gauge set is a ring of thin blades, one blade per size. Each blade usually has two working ends:
| End | Used for | What touches what |
|---|---|---|
| Stepped or square notch | Convex fillets (face bulges out) | Blade sits on one member, the notch corner meets the weld toe on the other |
| Curved or pointed end | Concave fillets (face dips in) | Both blade tips sit on the members, the center point reaches toward the weld face |
Reading a convex fillet
- Check the face first. Lay a straight edge across it, or just look. Convex means use the leg end.
- Pick a blade close to the specified size.
- Hold the blade square to the weld axis, flat on one member, and slide it until it meets the toe on the other member.
- Fit means the notch meets the toe with no gap. Too big a blade stands off; too small a blade passes under.
- Measure both legs this way. When the drawing calls for a single fillet size and the two legs gauge unequal, the shorter leg sets the weld size. A fillet specified with two different leg sizes is checked leg by leg against the drawing instead.
Reading a concave fillet
On a concave face the legs can look full while the throat is thin. The concave end checks the throat:
- Put the blade tips on both members, square to the weld.
- If the center point touches the weld face, the weld is at least that blade size.
- If you can see light between the point and the face, the weld is thinner than that blade at its throat. Step down one blade at a time until the point touches.
What the exam tests here. Using the wrong end. A concave fillet measured with the leg end reads big and gets accepted when it is undersized.
Length and location
Fillet size questions often ask how much of the length is undersize, not only by how much. Use the steel rule or caliper to measure the undersize length and note where it starts. Clause 2.4 is where structural fillet size and length tolerances live, so you will need both numbers.
The V-WAC gauge, hi-lo gauge and dial caliper
V-WAC gauge
The V-WAC (visual weld acceptance criteria) gauge is a flat plastic or metal card with several features on it. Typical ones:
- Undercut pointer or depth scale. Zero the pointer on the base metal next to the undercut, then move it into the deepest part of the groove and read the depth.
- Porosity circles or holes. Hold the gauge over a pore and find the smallest circle that covers it. That gives the pore diameter.
- Reinforcement step. Read how high the weld face stands above the base metal surface.
- Linear scale. Use the edge scale to measure a length, such as an undersize run of fillet, in inches or millimeters.
Read undercut at its deepest point, not the first point you touch.
Hi-lo gauge
The hi-lo gauge is mainly for pipe and plate fit-up. It measures:
- Internal misalignment (high-low). Put one finger on the inside surface of each member and read the offset on the scale. An inside step can trap slag and leave the root short of fusion.
- Root opening and land, with its tapered or stepped features.
Some models also read weld reinforcement height and wall thickness, so check which features yours has.
On a replica, misalignment at the root means the inside step, not the outside.
Dial caliper
The caliper, your most precise tool, measures four ways:
| Feature | Measures |
|---|---|
| Outside jaws | Thickness, bead width, specimen width |
| Inside jaws | Hole or gap width |
| Depth rod (tail) | Depth of a groove or pit |
| Step (end of jaws) | Height difference between two surfaces |
To read an inch dial caliper: read the main beam scale to the last full tenth visible, then add the dial reading in thousandths. Invented example: the beam shows 1.200 in and the dial needle is on 37, so the reading is 1.237 in.
What the exam tests here. Reading the gauge correctly, then choosing the feature that measures what the question asks for (depth, height, offset or width).
Zeroing tools and reading them consistently
Zero before every set of readings
- Caliper: clean the jaws, close them gently and check the needle sits on zero. If not, turn the bezel to zero. If you cannot, note the zero error and correct every reading. Invented example: the caliper reads 0.003 in with the jaws closed and 0.415 in on the part. The true reading is 0.415 minus 0.003, which is 0.412 in.
- V-WAC undercut pointer: set it to zero on flat base metal beside the area you will measure.
- Hi-lo gauge: check the fingers read zero on a flat surface before measuring offset.
Habits that keep readings repeatable
- Square to the surface. A tilted gauge reads high on height and low on depth.
- Eye level with the scale. Parallax adds error on a dial or a scribed line.
- Light from the side. A low-angle light makes undercut, overlap and pores stand out on a plastic replica. Use the magnifier for small indications.
- Measure the worst spot, twice. Find the deepest undercut or the highest reinforcement, measure, lift the tool and measure again. If two readings disagree, take a third.
- Write units every time. Note inch or millimeter beside each number. Use the conversion tables (Tables 16 to 18) or Annex V if the question and your tool use different units.
- Do not force a gauge. Pressing a blade into soft plastic changes the reading.
A quick tool routine per replica
- Read the label: application (structural, pipeline, pressure piping), joint and weld type.
- Look over the whole replica under side light and mark every indication on your scratch sheet.
- Measure size first (fillet gauge or caliper), then each indication with the right tool.
- Record each reading with units and location. Then move to the book.
Check yourself
The four-choice questions below are in the practice set. They cover the concave gauge end, caliper zero error and internal misalignment. Pick before you open the explanation.
Where to look in your own books
- CWI Part B Practical Exam Info (Rev. 03.01.2024): exam format, tool kit and replica instructions
- AWS CWI Part B Book of Specifications (2017), clause 2.4: structural fillet weld size and length tolerances
- Book of Specifications (2017), Annex V: formulas, conversions and fraction equivalents
- AWS B5.1:2025 Table 8.1: the Practical Applications subject areas and their minimum weights
- Background: AWS B1.11, Guide for the Visual Examination of Welds, for gauge use and visual examination practice