Weld Examination & Acceptance

Weld Examination & NDE Acceptance Guide

Select NDE methods (VT/PT/MT/RT/UT), verify examination extent by fluid service per ASME B31.3 Chapter VI, inspect 12 weld discontinuities with diagrams, and plan PMI, hardness & ferrite verification.

Coverage:

Core NDE methods

Primary surface and volumetric methods used for routine weld examination.

VTSurface

ASME B31.3

Visual examination

Detects Discontinuities

Surface-breaking cracksUndercutOverlapExcess/insufficient reinforcementMisalignmentArc strikesSurface porosity

Best For

Baseline examination of every weld: profile, size, surface condition and workmanship before any other method.

Material Limit:

All materials; requires adequate access and lighting.

Advantages

Fast, low cost, no consumables; the primary acceptance screen and prerequisite for other NDE.

Limitations

Surface only; subsurface flaws and tight cracks are not detectable; depends on inspector skill and access.

PTSurface

ASME BPVC Section V

Liquid penetrant testing

Detects Discontinuities

Surface-breaking cracksSurface porosityLack of fusion open to surfaceLaps and seams

Best For

Confirming surface-breaking flaws on non-magnetic materials such as austenitic stainless and nickel alloys; root and final pass checks.

Material Limit:

Any non-porous material; the usual choice where MT cannot be used (non-ferromagnetic).

Advantages

Portable, inexpensive, good sensitivity to fine surface cracks; simple to interpret.

Limitations

Surface-breaking flaws only; needs clean, dry surface; temperature limits; hazardous with some cleaners.

MTSurface / near-surface

ASME BPVC Section V

Magnetic particle testing

Detects Discontinuities

Surface cracksSlightly subsurface cracksLack of fusion near surfaceToe cracks

Best For

Ferromagnetic welds where near-surface sensitivity is wanted; alternative to PT on carbon and low-alloy steel.

Material Limit:

Ferromagnetic materials only (carbon and low-alloy steel); not usable on austenitic stainless or nickel alloys.

Advantages

Detects near-surface flaws PT cannot; fast on ferritic steel; low cost.

Limitations

Ferromagnetic only; orientation sensitive (two directions needed); may require demagnetisation and surface prep.

RTVolumetric

ASME BPVC Section V

Radiographic testing

Detects Discontinuities

PorositySlag inclusionsIncomplete penetrationLack of fusionCracks (orientation dependent)Burn-through

Best For

Volumetric examination of butt welds where a permanent image record and good volumetric flaw detection are required.

Material Limit:

Most materials; interpretation depends on thickness and density.

Advantages

Permanent record; excellent for volumetric (rounded) flaws; well-understood acceptance basis.

Limitations

Radiation safety and exclusion zones; poor for tight planar flaws normal to the beam; access to both sides; slower.

UTVolumetric

ASME BPVC Section V

Conventional ultrasonic testing

Detects Discontinuities

Planar cracksLack of fusionIncomplete penetrationLaminationsSlagWall loss / thickness

Best For

Manual volumetric examination of thicker welds and targeted detection or sizing of planar discontinuities.

Material Limit:

Best on fine-grained ferritic steel; coarse-grained austenitic welds need qualified techniques.

Advantages

Good planar-flaw detection and depth sizing; single-side access; immediate results and no radiation hazard.

Limitations

Highly operator/procedure dependent; needs calibration blocks and couplant; geometry and grain structure can mask flaws.

Advanced ultrasonic techniques

Encoded techniques for recordable coverage, detection and flaw sizing.

PAUTVolumetric

ISO 20601

Phased array ultrasonic testing

Detects Discontinuities

Planar cracksSidewall or interpass lack of fusionIncomplete penetrationSlag inclusionsEmbedded volumetric indications

Best For

Encoded multi-angle examination of butt welds where recordable coverage, flaw location and sizing are required.

Material Limit:

Most effective on fine-grained ferritic steel; austenitic, dissimilar and complex welds require specifically qualified probes and procedures.

Advantages

Multiple beam angles from one probe position; encoded images, repeatable coverage and improved characterization of oriented planar flaws.

Limitations

Requires a qualified scan plan, calibration blocks and skilled interpretation; geometry, near-surface zones and coarse grain can limit coverage.

TOFDVolumetric

ISO 10863

Time-of-flight diffraction

Detects Discontinuities

Crack tipsEmbedded planar discontinuitiesLack of fusionIncomplete penetrationThrough-wall flaw height

Best For

Encoded detection and through-wall sizing of embedded planar flaws in full-penetration welds, commonly paired with PAUT.

Material Limit:

Primarily suited to simple-geometry, full-penetration welds in low-attenuation materials; ISO 10863 addresses thicknesses from 6 mm.

Advantages

Accurate through-wall sizing, good detection independent of flaw orientation and a permanent encoded data record.

Limitations

Has lateral-wave and back-wall dead zones near the surfaces; gives limited flaw-type characterization and normally needs complementary pulse-echo coverage.

Special-purpose examination

A targeted method selected for specific materials, surfaces or access conditions.

ETSurface / near-surface

ISO 17643

Eddy current testing

Detects Discontinuities

Surface-breaking cracksNear-surface planar flawsToe and grinding cracksNear-surface lack of fusion

Best For

Rapid surface and near-surface examination of electrically conductive welds, including some coated surfaces where PT or MT is impractical.

Material Limit:

Electrically conductive materials only; permeability changes, weld geometry, coating thickness and rough surfaces affect the signal.

Advantages

No couplant, immediate results, sensitive to fine cracks and can often examine through thin nonconductive coatings.

Limitations

Shallow penetration and geometry-sensitive signals; requires reference standards and skilled interpretation and is not a volumetric weld examination.

Process and integrity verification

Controls fabrication conditions and verifies leak tightness; it does not replace required weld-quality NDE.

IPEProcess control

ASME B31.3

In-process examination

Detects Discontinuities

Incorrect joint preparation or fit-upContamination and inadequate cleaningWPS variable deviationsRoot-pass defects before burialPoor interpass condition

Best For

Staged verification during fabrication when joint preparation, root condition and welding controls can still be observed and corrected.

Material Limit:

All welded materials; hold points and observations must be defined in the approved inspection and test plan.

Advantages

Finds preventable conditions before they are hidden by later passes; supports traceability and early corrective action.

Limitations

Does not demonstrate final volumetric soundness and cannot replace required post-weld RT, UT, surface examination or leak testing.

LTLeak integrity

ASME BPVC Section V

Leak testing

Detects Discontinuities

Through-wall leakagePressure-boundary leakageLocal joint or seal leakage

Best For

Final verification of pressure-boundary tightness using an approved pressure-change, bubble or tracer-gas technique.

Material Limit:

Applicable test fluid, pressure, temperature and sensitivity depend on system design, material compatibility and the approved procedure.

Advantages

Directly demonstrates leak tightness and can examine an assembled system rather than only an individual weld.

Limitations

Does not detect or size non-through-wall cracks, lack of fusion or embedded flaws and must not be treated as a substitute for weld-quality NDE.