PT vs MT for Weld Pores: Which NDT Method Should Buyers Specify?

Sources used:
- ASNT Introduction to Nondestructive Testing
- ASNT Ultrasonic Testing overview

Why Buyers Ask PT vs MT

Searches like "PT vs MT searching for pores" usually come from buyers or inspectors who need a simple answer before placing an order. The correct answer depends on the material, the defect location, the surface condition and the acceptance standard.

PT and MT are both useful, but neither is a universal substitute for RT or UT.

What PT Is Good At

PT means liquid penetrant testing. It is used to reveal surface-breaking indications on non-porous surfaces. It can be used on many metallic materials, including non-magnetic stainless steels, when the surface is suitable.

PT is useful for checking surface cracks, laps, seams or open surface discontinuities. If a pore is open to the surface, PT may reveal it. If the pore is fully internal, PT will not find it.

What MT Is Good At

MT means magnetic particle testing. It is used on ferromagnetic materials and can reveal surface and near-surface discontinuities. It is often used on carbon steel and low-alloy steel components.

MT is not suitable for non-magnetic stainless steels. It also should not be treated as a full volumetric examination method.

What About Weld Pores?

The word "pore" can mean different things. A surface-open pore may be visible by PT or MT depending on material and test condition. Internal porosity in a weld normally requires a volumetric method such as RT or UT, if the project specification requires detection.

Do not write only "PT/MT for weld pores" in an RFQ unless the inspection scope is clear. State whether the concern is surface condition, near-surface discontinuities, or internal weld soundness.

When RT or UT Is Needed

ASNT describes ultrasonic testing as a method that uses high-frequency sound waves and can be used for thickness measurement and internal flaw detection. RT is also commonly used for weld volumetric examination when the project specification requires radiographic evidence.

The choice between RT and UT depends on weld geometry, material, thickness, access, acceptance criteria, safety requirements and client specification.

RFQ Wording Buyers Can Use

"Supplier shall perform NDT according to project specification. PT shall be used for surface-breaking indications where specified. MT shall be used only for ferromagnetic materials where specified. Internal weld soundness shall be verified by RT or UT when required by the drawing, code or inspection plan."

This wording avoids forcing the wrong method onto the wrong defect.

Quick Selection Table

Related Products

• Carbon steel butt-weld fittings
• Stainless steel pipe fittings
• Flanges requiring surface inspection
• Fabricated spools with weld inspection packages

Further Reading

• NDT for Pipe Fittings: PT vs MT vs UT vs RT Guide
• ASME B16.9 Pre-Shipment Inspection Checklist