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NDT Methods Comparison Chart: Which Test Finds What

Choosing between penetrant, magnetic particle, ultrasonic or radiographic testing starts with what you need to find and where it sits in the part. This chart gives a quick side by side so you can have an informed conversation with your NDT supplier.

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Method	Abbrev.	Typically finds	Reach	Main limitations
Visual testing	VT	Surface discontinuities, weld profile, corrosion, misalignment	Surface	Depends on lighting, access and inspector skill
Liquid penetrant testing	PT	Surface breaking cracks, laps, porosity	Surface breaking only	Needs clean, non porous surface; smeared metal can hide cracks
Magnetic particle testing	MT	Surface and near surface cracks and laps	Surface and slightly subsurface	Ferromagnetic materials only; field direction matters
Ultrasonic testing	UT	Internal flaws, laminations, thickness loss, weld defects	Volumetric	Needs couplant and skilled interpretation; rough or complex geometry is hard
Phased array ultrasonic testing	PAUT	Weld flaws, corrosion mapping, composite defects	Volumetric	Equipment cost and procedure development effort
Radiographic testing	RT	Porosity, inclusions, voids, lack of fusion, wall thickness	Volumetric	Radiation safety controls; tight planar cracks may be missed if misaligned
Computed tomography	CT	3D internal voids, porosity, assembly condition	Volumetric	Part size and density limits; high cost per part
Eddy current testing	ET	Surface and near surface cracks, conductivity, coating thickness, tube wall loss	Surface and near surface	Conductive materials only; limited depth
Leak testing	LT	Leaks in vessels, seals and welds	Through wall	Method must match required leak rate and medium
Acoustic emission testing	AE	Active crack growth and corrosion in loaded structures	Whole structure	Needs loading and noise control
Infrared thermography	IR	Delaminations, disbonds, moisture, hot spots	Near surface	Needs thermal contrast and emissivity control
Positive material identification	PMI	Wrong alloy or grade	Surface composition	Light elements such as carbon are not read by common XRF units

This is a screening guide for method selection. The applicable specification, drawing note or customer flow down decides the method, procedure and acceptance criteria. NDT personnel are usually qualified to a written practice such as ASNT SNT-TC-1A or an equivalent standard.

Connect NDT records to supplier lots

Optional: we can explore how NDT certificates could be matched to purchase orders and inspection lots in your ERP.

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How to use the chart

Search by a defect name, material issue or method. Look at the Reach column first: surface methods cannot find buried flaws, and volumetric methods are usually not the first choice for fine surface cracks. Then check limitations against your material. For example, magnetic particle only works on ferromagnetic alloys, so aluminum or austenitic stainless parts need penetrant or eddy current instead.

Selecting and specifying NDT

Most of the time the customer or specification names the method and acceptance class. Where it does not, choose the method for the failure mode you fear most, then write the procedure reference, sample plan and acceptance criteria on the purchase order or inspection plan. Combine methods when needed, such as penetrant on machined surfaces plus ultrasonic on critical weld volumes.

State the method and the governing standard on the PO
Require certification level of the examiner
Define 100 percent or sample inspection clearly
Ask for written results to be attached to the lot

Common mistakes

Treating NDT as a pass or fail stamp without checking the procedure, using penetrant after shot peening or heavy machining that has smeared the surface, and forgetting post inspection cleaning and demagnetizing. Also confirm that the subcontractor holds the right scope of accreditation or customer approval, because many aerospace primes approve NDT sources by process.

Frequently Asked Questions

Which NDT method is best for surface cracks?

Liquid penetrant works on most nonporous materials and finds surface breaking cracks. Magnetic particle is faster on ferromagnetic parts and also finds shallow subsurface flaws. Eddy current suits conductive parts and automated scans.

Why can't magnetic particle testing be used on aluminum?

It relies on a magnetic flux leakage pattern that attracts iron particles. Aluminum and austenitic stainless steels are not ferromagnetic, so no usable leakage field forms. Use penetrant or eddy current instead.

Is radiography better than ultrasonic testing?

Neither is better in general. Radiography gives a permanent image and suits volumetric flaws like porosity. Ultrasonic finds planar flaws such as cracks and lack of fusion more reliably and has no radiation hazard.

Who qualifies NDT personnel?

Employers qualify and certify personnel under a written practice based on a standard such as ASNT SNT-TC-1A, ISO 9712 or NAS 410 for aerospace. Customer flow downs may add requirements.

If NDT results arrive as PDFs from subcontractors, Netray can help tie them to purchase orders and inspection lots in your ERP.

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