The short answer
NDT should be specified only when the defect mode and material justify it. PT, MT, and UT are tools, not prestige labels.
What the main methods do
PT, or liquid penetrant testing, is used to reveal surface-breaking discontinuities on suitable nonporous materials. MT, magnetic particle testing, is for ferromagnetic materials and also looks for surface and near-surface discontinuities. UT, ultrasonic testing, looks deeper into the material for internal indications when geometry and material support it.
Each method has a lane. Stay in it.
When to specify each one
Use PT on nonmagnetic metals when surface cracks are the concern. Use MT on ferromagnetic steels when near-surface defect detection is needed. Use UT when internal soundness matters and the part geometry allows meaningful ultrasonic inspection.
Do not write generic 'NDT required' and expect the supplier to guess the method.
What drives cost
Part geometry, surface condition, lot size, acceptance standard, technician qualification, and whether the work must be done by an accredited source all drive price. NDT on a clean simple geometry is one thing. NDT on a complex coated part with tight deadlines is another.
NDT is a real process with real schedule consequences.
How to buy it correctly
State method, acceptance criteria or governing spec, coverage area, timing in the route, and reporting requirements. If only a specific region is critical, define that region instead of forcing full-part testing with no reason.
Testing should answer a real risk question.
What an experienced buyer does next
Related reading: Surface treatment quality: how to inspect anodizing, plating, and heat treat and Statistical process control (SPC) in CNC machining: a buyer's primer.
The right move is usually to define the real functional requirement, remove the decorative requirements, and let the supplier build a route around what actually matters.
Comparison table where relevant
| Method | Best for | Key limit |
|---|---|---|
| PT | Surface-breaking flaws on nonporous parts | Does not see deep internal flaws |
| MT | Surface and near-surface flaws in ferromagnetic materials | Material must be ferromagnetic |
| UT | Internal flaw detection | Geometry and access matter |
| Generic 'NDT required' | Confusion | Not a valid requirement |
How to specify this in your RFQ
Specify the NDT method, standard, acceptance level, and whether the whole part or only critical regions need coverage. If technician certification or accredited sources matter, state that too. Otherwise the quote will either be inflated or incomplete.
A clean RFQ does not just list requirements. It separates must-haves from preferences so the supplier can optimize where it is safe.
Have a part that needs quoting? Email your drawings to rfq@precisionmachining.co -
we return a competitive quote within 24 hours. Phone: +1 312-579-0808.