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CASING INSPECTION

Shearography, X-Ray, and NDT: How Casings Are Actually Inspected Before a Retread

Some casing defects can't be caught by eye or hand. Here's what shearography and X-ray actually detect, where they fit in the industry today, and what it means for a shop that doesn't run one.

Published September 17, 2026 · Good Hope Retreaders

Our 5-point casing inspection guide covers what every shop should do before a casing goes anywhere near a buffer: a thorough visual and tactile check for structural damage, age, and repair history. That inspection is the right foundation, and it catches the great majority of casings that shouldn't be retread. But there's a category of defect it can't catch — because it's hidden inside the belt package, invisible to the eye and untouchable by hand. That's where non-destructive testing (NDT) technology — shearography, X-ray, and ultrasound — comes in.

This post is about that technology: what it actually does, why it exists, and — just as honestly — where it fits relative to the size of shop you're running.

The defect a trained hand can't find

The failure mode NDT technology is built around is belt separation — the steel belts inside a radial casing losing adhesion to each other or to the body ply. It's typically buried inside the belt package itself, which means a technician running a visual and tactile inspection, even a rigorous one, generally cannot detect it. Industry sourcing on this is consistent: retreaders that run shearography equipment, such as Marangoni, use it specifically to catch belt separations that a standard inspection misses.

Shearography: how it actually works

Shearography is an optical technique. The casing is loaded into a sealed chamber, and a vacuum is drawn around it while laser sensors monitor the surface. Where the belt package is sound, the tire's surface responds evenly to that pressure change. Where there's a hidden separation, a trapped air pocket, or compromised adhesion between plies, that spot deforms slightly differently than the surrounding rubber — and the laser interferometry picks up that tiny, localized displacement. The system renders it as a visible defect map, without ever cutting into the tire.

Purpose-built systems have gotten fast. ZEISS Optotechnik's INTACT 1360-X, for example, is built to scan a casing bead-to-bead — separations, blisters, and areas of undercuring — in roughly 55 seconds including load and unload. That speed is what makes shearography viable as a standard, every-casing station in a high-volume plant rather than a spot-check tool.

X-ray and ultrasound: the other two tools

X-ray (radiographic) inspection is the other NDT method in wide use. It's a real-time technique that's highly sensitive to foreign material embedded in the casing and to porosity — genuinely useful defects to catch before you commit tread and labor to a bad carcass. Its limitation is physics: X-ray sensitivity depends on material density, so some of the subtler bonding irregularities that shearography is specifically built to detect can be harder for radiography to resolve. Ultrasound is used as a third, complementary NDT method in some operations, generally for a different slice of the same internal-defect problem. In practice, the technologies overlap rather than replace one another — which is part of why TRIB-certified retreaders are required to run shearography or X-ray on every casing, not treated as interchangeable optional extras.

Where this sits in the industry today

Michelin Retread Technologies runs its proprietary Casing Integrity Analyzer — a shearography system paired with dedicated software — in 100% of its MRT plants, and requires it on every casing after the initial inspection. Tom Brennan, president of Michelin Retread Technologies, has described the software layer as being as important as the imaging itself: the system is built specifically so the operator interprets the shearography output correctly, rather than leaving that judgment call to guesswork.

That software layer is where the newest development is happening. In March 2026, Michelin launched TreadVision, which applies AI-based vision classification to Casing Integrity Analysis (shearography) results — the goal being more consistent, more objective quality decisions than relying purely on an individual operator's read of the imaging, at the scale of a large plant network.

What this means if you're not running an NDT line

Here's the honest part: shearography and X-ray systems are a plant-scale capital investment, built for operations running high casing volume through a dedicated inspection station every shift. That's not the reality for most independent and mid-size retread shops, and it doesn't need to be. What it does mean is that visual and tactile inspection discipline matters more, not less, at that scale — a properly run 5-point check, done on an inspection spreader that actually opens the casing up for a real look at the interior, by a technician who knows what disqualifying damage looks like, catches the overwhelming majority of casings that shouldn't go back into service.

NDT technology is the layer above that — worth knowing about, worth understanding as an upgrade path if your volume and risk profile ever justify it, and useful context when you're evaluating why a large branded retreader's quality claims look the way they do. It isn't a prerequisite for running a careful, defensible in-house inspection process today. Good casing prep starts with the fundamentals: our guides on buffing and rasping for bond quality and skiving casing repair before retreading cover what comes next once a casing has passed inspection.

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