The Test Plate
One piece of steel — fitted, tacked, and welded, then judged the way an inspector judges it: visual criteria first, a bend test after, and any failure read as information. · 13 min
The course ends the way a welding qualification does: on one piece of steel. A fillet-weld test plate is a tee joint — a web plate stood on a flange plate — fitted, tacked, welded on both sides, and then judged twice. First an inspector's eyes and gauges check the outside against written acceptance criteria. Then a bend test folds a cut strip of the weld — a coupon — to expose what the surface hides. Nothing here is new; it is everything already learned, performed in order.
Guess before you learn
A finished fillet passes every visual check — right size, even profile, no cracks, no undercut. Can the inspector be sure the weld is sound?
Visual inspection reads geometry; it cannot see inside. A bead can sit on cold, unfused plate and still look handsome from above — folio 11's lack of fusion, hiding in plain sight. That is what the bend test is for: it stretches the weld until anything unfused opens where you can see it.
9–12
3–5
An inspector checks a weld against a written list: legs the right size, surface even, no cracks, no deep notch along the edges. Anything on the list that fails means the weld is not accepted — no matter how good it looks otherwise.
Then comes the harder test. A strip is cut across the weld and bent into a U shape around a bar. Bending stretches the metal, and if any part of the weld never truly fused, the stretch pulls it open where everyone can see it.
6–8
Visual inspection comes first because it is cheap and catches most trouble: leg size measured with a fillet gauge, a flat-to-slightly-convex profile, even ripples, no cracks anywhere, undercut no deeper than the criteria allow, no visible porosity. A crack of any size rejects the weld outright.
The guided bend test is destructive and honest: a coupon cut across the weld is forced around a die of set radius, stretching its outer face hard. Lack of fusion, trapped slag, or clustered porosity opens under that strain. Acceptance is written the same way: no opening longer than the stated limit.
9–12
The two tests split the problem. Visual criteria police geometry — size, profile, and surface discontinuities — because geometry concentrates stress: undercut is a notch, and a notch is where fatigue starts. The bend test polices fusion, which no gauge can reach.
Guided bends come in variants: a root bend puts the weld's root in tension — the place most likely to hide lack of fusion — while a face bend stretches the face. Strain at the outer surface runs near 20 percent, far past anything the weld will meet in service. That excess is the point: the test buys margin.
K–2
You welded two plates into one piece. Now check your work. Look closely: is the weld the right size? Any holes or cracks?
Looking is not enough. Cut a strip and bend it hard around a bar. A sound weld stretches and holds. A weld with a gap inside opens up.
Undergrad
Terminology draws a line worth keeping: a discontinuity is any interruption in the metal's structure; it becomes a defect only when it exceeds the acceptance criteria of the governing code. Inspection is measurement against a standard, not a search for perfection — every weld ever made contains discontinuities.
The logic of qualification is sampling: one plate, welded under test conditions, stands in for the welder's future work. That is why procedure matters as much as outcome — the test certifies a person executing a process (AWS calls it performance qualification), not one fortunate bead.
Postgrad
Beyond workmanship tests sit the nondestructive methods, each with its own physics and blind spots: radiography reads density and favors volumetric flaws; ultrasonics reads acoustic interfaces and favors planar ones — the dangerous ones, in fracture-mechanics terms; penetrant and magnetic-particle methods read only the surface and near-surface.
Modern codes increasingly frame acceptance as fitness-for-service: a flaw is sized, stressed, and assessed (BS 7910, API 579) rather than rejected on workmanship limits alone. Probability-of-detection curves, not certainty, describe every inspection method — a bend test is best understood as a high-detection-probability sample of one.
coupon
A strip cut across a test weld for destructive testing — bent or broken to reveal the weld's internal condition.
Visual inspection runs down a written list, in order, with good light and a fillet gauge — a stamped steel template held into the weld's corner to check leg size and profile at once. You are measuring, not admiring: each criterion has a number or a plain pass condition, and one hard rule sits above the rest — a crack of any length, anywhere, rejects the weld. Everything else is judged against its stated limit.
The bend test asks the question no gauge can: did the metal truly fuse? A coupon is sawn across the weld, its cut edges ground smooth so a stray nick cannot start a false failure, and forced around a die into a U. The outer face stretches hard — near twenty percent — and any place where fusion never happened opens under that stretch into a visible line or hole. Acceptance is again written down in advance: no single opening longer than the stated limit, commonly 1/8 in.
Read a failed coupon, cause to cure — the steps fade as you master them
The coupon opened along the line where weld metal met the plate
Lack of fusion — the weld sat on plate it never melted
Too little heat, or a work angle that favored one plate and left the other cold
Raise the amperage one step and hold the electrode near 45° between the plates
Note
A failed coupon costs one plate and an afternoon. The same defect inside a trailer hitch costs far more. The test is cheap on purpose.
That is Welding I. You can dress for the arc, set the machine, strike, and run a bead you can read; you know the five joints, the two welds, the symbol that orders them, and the sequence that keeps the work square; and you can judge the result the way an inspector does — criteria first, evidence always. Welding II adds positions 3 and 4, open roots, and the certification bench.
Practice — new ink and old, interleaved
1.A bead sits proud on the plate, and a chisel pops a whole section off cleanly. What was it?
2.The plate passed visual inspection but failed the bend. Which statement is true?
3.The drawing calls for a 6 mm fillet. A beginner runs 12 mm to be safe. What did the joint actually gain?
4.In one sentence: why is a fillet's strength measured through its throat rather than along its leg?
5.Why does angular distortion happen at a fillet — why do the plates tip instead of just drawing together?
6.Acceptance allows no single opening on the bent coupon longer than 1/8 in (0.125 in). A flaw measures 0.10 in. What is the margin, in inches, between the flaw and the limit?
7.Name four visual acceptance criteria for a fillet weld.
Leg size to the callout; flat-to-slightly-convex profile with even ripples; no cracks of any size; undercut within its limit — plus no surface porosity.
How close were you? Grade yourself honestly — it sets your review date.
8.Order the judging stages of a test plate.
- Clean to bare metal
- Visual inspection with gauge and light
- Cut and prepare coupons
- Guided bend and read the result
9.Match the evidence to the finding.