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How To Inspect Welding Quality? Here Are Four Common Testing Methods To Ensure Welding Meets Standards.
How To Inspect Welding Quality? Here Are Four Common Testing Methods To Ensure Welding Meets Standards.
Views: 0 Author: Site Editor Publish Time: 2026-01-30 Origin: Site
Welding quality directly governs joint strength, safety and service life. Defective welds can cause breakage, leakage, scrap or even industrial accidents. Many companies ship faulty parts simply because they lack a standard inspection routine, which raises rework costs and damages brand reputation. In fact you don’t need complex gear to control weld quality—master four common tests (visual, penetrant, ultrasonic, destructive) and you cover the whole spectrum from quick screening to accurate verification. This article explains the operation key-points and application scope of each method; first-time inspectors and experienced QA departments can copy the workflow straight away.
Core principle: follow the “shallow-to-deep, surface-to-core” logic—find obvious surface flaws first with simple means, then hunt for hidden internal defects with professional methods, and finally carry out spot destructive tests to prove overall conformity. This saves inspection cost and boosts efficiency.
I. Visual inspection – fastest, cheapest, everyone can do it
Visual inspection is the first line of defence; no special equipment or skill is required. In mass production it catches ≥80 % of obvious surface defects in seconds.
1. What to look for
Weld size: width, height, length within drawing tolerance (±1 mm is common).
Steps: (i) Clean spatter, rust, oil; (ii) Scan the whole joint under strong light, especially start/stop and toe areas; (iii) Measure leg length, throat, overall length; (iv) Reject or mark for repair if cracks, large pores or undersize are seen.
3. Pitfalls
Poor lighting hides hairline cracks—always use a flashlight.
Remove slag gently; don’t gouge the surface and create “false” defects.
Never ignore a hairline crack—it may propagate through the wall.
II. Penetrant testing (PT) – finds tiny surface/near-surface openings
PT is a low-cost, non-destructive method for detecting micro-cracks or pores ≤2 mm deep that the eye cannot see. It suits almost all metals and complex shapes.
Principle Capillary action pulls coloured dye into surface openings; excess dye is wiped off; a white developer draws the dye back out, revealing the flaw.
Tools & procedure Aerosol cans: cleaner, penetrant, developer; non-abrasive cloth; optional hair-dryer.
Steps: (i) Grind/degrease a 20 mm band along the weld; (ii) Spray penetrant, keep surface wet 10–20 min; (iii) Wipe off excess, clean perpendicularly to the joint; (iv) Spray a thin developer layer; (v) After 5–10 min inspect under daylight—coloured lines = cracks, dots = porosity.
Scope & limits Good for: surface-breaking defects on rough or complex shapes (pipe fittings, cast housings).
Limits: cannot see internal flaws; surface roughness may give false calls; unsuitable for porous materials (cast iron).
III. Ultrasonic testing (UT) – the backbone for internal defects
UT is the mainstream non-destructive method for internal discontinuities in thicker (≥8 mm) welds: lack of fusion, buried cracks, slag, porosity. It is indispensable for load-critical or pressure-critical joints.
Principle A piezo-electric probe sends high-frequency sound into the weld. Sound reflects at interfaces; the time-of-flight and echo height tell the operator the location and size of a reflector.
Equipment & steps Flaw detector, twin-angle or straight probe, coupling paste (oil or glycerine), calibration block.
Steps: (i) Grind weld cap flush, remove rust/paint; (ii) Calibrate on a reference block; (iii) Apply couplant, scan probe parallel and perpendicular to weld axis; (iv) Mark indications above evaluation level; (v) Plot position and length, classify per code (ISO 17640, AWS D1.1, GB/T 11345).
Advantages
Fully non-destructive; can retest the same joint.
Deep penetration (several metres on large forgings).
Fast scanning—suitable for high-volume inspection.
Gives exact depth and length for repair planning.
IV. Destructive testing – proof of strength and ductility
Small samples are removed and broken to verify that the WPS actually delivers the required mechanical properties. It is the only way to see “ultimate reality”.
Most common tests
(a) Tensile test – measures ultimate tensile strength (UTS). Acceptance: weld UTS ≥90 % of base-metal UTS and fracture outside the weld or meet minimum code value.
(b) Side-bend or root-bend – verifies ductility and freedom from lack-of-fusion. No single crack >3 mm on the tension face after 180° bend over a mandel Ø = 4 t.
Sampling
Usually 3–5 pieces per batch or per 50 m of weld. For new WPS qualification test plates, two tensiles and four bends are typical.
Notes
Samples must be representative (same material, thickness, WPS).
Machines must be calibrated; edge cracks from rough cutting must be removed.
Combine with NDT: NDT finds location, DT proves properties.
V. Shop-floor workflow (copy & paste)
Step 1 – 100 % visual by welder/operator; immediate repair or scrap.
Step 2 – PT on critical fillets or UT on thick butt welds (spot-check or 100 % as required by code).
Step 3 – Destructive sample each lot; expand sample if any fail.
Step 4 – Final release only after all three steps pass plus documentation.
Adapt frequency and method to your industry: medical devices and auto parts may need 100 % UT + lot destructives; general hardware can rely on visual + periodic PT/bend.
VI. Quick pitfall list
Don’t skip visual—surface cracks are often the “root” of later UT rejects.
PT fails when parts are dirty; surface prep is 80 % of the result.
UT needs daily calibration and a trained operator; wrong probe angle = missed lack-of-fusion.
Destructive samples must be exactly the same WPS; otherwise the test is meaningless.
Master these four methods and you will catch defects early, cut rework cost and guarantee that every welded product leaving your plant is safe and code-compliant.
If you have welding machine requirements, please contact Ms. Zhao
Founded in 2006, PDKJ is a professional supplier of welding automation solutions. The company has passed the ISO9001 international quality management system certification, has more than 90 officially authorized and applied national patents, and a number of core technologies in the welding field fill the technical gap at home and abroad. It is a national high-tech enterprise.
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