Nondestructive testing, or NDT, evaluates a component without making it unusable. The correct method depends on the product form, manufacturing route, defect type, material and governing code. Requiring “full NDT” without naming the method and acceptance criteria can lead to inconsistent quotations and inspection results.
Visual testing
Visual testing is the foundation of inspection. It can identify surface damage, poor weld profile, undercut, incomplete cleaning, arc strikes, marking problems and dimensional irregularities. Adequate lighting, access and trained personnel are necessary. Visual acceptance should be linked to the applicable product specification, construction code or agreed procedure.
Liquid penetrant testing
Liquid penetrant testing is widely used on nonporous stainless steel to reveal surface-breaking discontinuities. After cleaning, penetrant enters openings at the surface. Excess penetrant is removed and a developer helps draw out visible indications.
PT can be applied to formed areas, machined surfaces and welds when specified. It will not reveal subsurface defects. Surface cleanliness, dwell time, temperature and final interpretation affect reliability.
Radiographic testing
Radiography uses penetrating radiation to produce an image of internal features. It is commonly associated with weld examination and can be effective for volumetric discontinuities and weld-profile information. Access, component geometry, thickness, safety controls and image quality influence feasibility.
For stainless steel fittings manufactured with fusion welds, the material specification and class designation may define the required examination. Purchasers should identify the fitting class and any additional radiography requirement in the order.
Ultrasonic testing
Ultrasonic testing introduces high-frequency sound into the material and interprets reflected signals. It can detect certain internal discontinuities and measure thickness. Geometry, coarse grain structure, surface condition and operator technique can make examination of small or complex fittings challenging.
UT is not automatically interchangeable with RT. Any substitution should be permitted by the governing specification and supported by a qualified procedure and acceptance criteria.
Leak and pressure testing
Pressure or leak testing addresses pressure integrity rather than serving as a complete replacement for NDT. The component standard, piping code and purchase order determine whether hydrostatic, pneumatic or another leak test is required. Pneumatic testing stores substantial energy and requires a carefully controlled safety procedure.
How to specify NDT in an inquiry
- Identify the component, material and manufacturing class.
- Name the examination method: VT, PT, RT, UT or another method.
- Define the extent, such as every item, every weld or a sampling percentage.
- State the governing procedure and acceptance criteria.
- Specify personnel qualification requirements.
- Identify report, image and record-retention needs.
- Clarify witness and hold points before production.
ASTM A403/A403M distinguishes fitting classes partly by construction and NDE requirements. ASTM A182/A182M covers forged stainless steel flanges and related pressure components, while supplementary examination may depend on the order and applicable construction code.
A useful NDT plan targets credible manufacturing defects and service risks. It should be agreed during quotation so examination access, schedule and cost are built into the production route.