Weld Inspection Services | NDT Methods for Weld Quality Control

NDT Hub Guide · Updated February 2026

Weld inspection is the single largest application of NDT — accounting for approximately 15% of all industrial NDT volume globally. From AWS D1.1 structural steel to ASME Section IX pressure equipment and API 1104 pipeline welds, the right inspection method is critical to weld quality and fitness for service.

The weld inspection requirement is driven by three factors: the inherent variability of the welding process (which can produce defects even with qualified welders and qualified procedures); the service conditions (pressure, temperature, cyclic loading, corrosive environment); and the consequence of failure (safety, environmental, commercial). Weld inspection verifies that the manufactured product meets the acceptance criteria of the governing code — AWS D1.1, ASME Section VIII/B31.3, API 1104, or another applicable standard.

Each NDT method is sensitive to different defect types and configurations. The governing code specifies which methods are required — but understanding the capability of each method is essential to selecting the right inspection strategy.

Understanding the cause and morphology of each weld defect type is essential to selecting the appropriate NDT method. Planar defects (cracks, lack of fusion) are best detected by UT/PAUT; volumetric defects (porosity, inclusions) are best detected by RT; surface defects by MT/PT.

Note: Best NDT method depends on defect orientation, weld geometry, and governing code requirements. Multiple methods may be specified.

The governing code for a weld inspection is determined by the type of equipment, material, and jurisdiction. Each code specifies the required NDT methods, technique requirements, acceptance criteria, and documentation requirements. Using the wrong code — or applying acceptance criteria from one code to welds qualified under another — is a common and potentially dangerous error.

Phased Array Ultrasonic Testing (PAUT) has become the dominant volumetric weld inspection technique in the oil & gas, construction, and pressure equipment sectors. This is driven by technical advantages, safety benefits, and economics:

A compliant weld inspection program requires three interrelated documents: the Welding Procedure Specification (WPS), the Procedure Qualification Record (PQR/WQR), and the NDT procedure. Together these govern how the weld is made and how it is inspected.

Atlantis NDT provides ASNT Level III weld inspection consulting — procedure development per AWS D1.1, ASME V, and API 1104; PAUT technique file development; personnel qualification review; and Level III review and signature services. Contact our team for weld inspection training (RT, PAUT, MT, PT Level II) or procedure development support.

Our ASNT Level III engineers develop AWS D1.1, ASME V, and API 1104 weld inspection procedures, qualify PAUT techniques, and provide Level III review services globally.

What this page covers

What Is Weld Inspection?
NDT Methods for Weld Inspection
Weld Defect Types and Best NDT Method
Governing Codes for Weld Inspection
PAUT for Weld Inspection — Why Phased Array Is Replacing RT
Weld Inspection Procedure — WPS, WQR, and Technique Qualification
Industries Served
Weld Inspection Consulting by Location
Related NDT Methods & Resources
Weld Inspection — Frequently Asked Questions
Weld Inspection Consulting & Training
Key Fact: Weld Inspection Scope
On This Page
Weld Inspection Codes

Key points covered

What is the difference between AWS D1.1 and ASME Section IX for weld inspection?
What is a Welding Procedure Specification (WPS) and why is it important for NDT?
Why is Phased Array UT (PAUT) replacing radiographic testing for weld inspection?
Primary volumetric inspection method for most weld types. S-scan beam steering provides full weld volume coverage in a single pass. Replaces RT in most onshore applications. Excellent sensitivity to planar defects (cracks, lack of fusion). ASME V App IV, AWS D1.1 Annex K.
Traditional volumetric weld inspection. Film RT and digital radiography (CR/DR). Excellent for rounded volumetric defects (porosity, inclusions). Produces permanent film record. ASME V Art 2, API 1104, AWS D1.1. Radiation hazard requires exclusion zone.
Surface and near-surface crack detection in ferromagnetic weld metal and HAZ. Wet fluorescent MT (WFMT) is highly sensitive. Used for root pass inspection, finished weld surfaces, and repair welds. ASME V Art 7, EN ISO 17638.
Surface-breaking defect detection. Applicable to austenitic stainless steel, aluminium, titanium welds where MT is not usable. Used for root face and cap visual confirmation, repair welds. ASME V Art 6, ASTM E1417.
Mandatory first-stage inspection for all welds. Checks profile, surface condition, undercut, overlap, cracks, crater defects, and weld geometry. Must be completed before any other NDT. AWS D1.1 Table 9.1 dimensional acceptance criteria.
Time of Flight Diffraction — paired with PAUT for thick-section weld inspection. Superior defect sizing accuracy for through-wall height measurement. ASME V Appendix III, EN ISO 10863. Used for fitness-for-service assessments.
Gas entrapment during solidification; moisture in electrode coating, base metal, or shielding gas
RT (excellent), PAUT (good for larger clusters), PT (surface pores only)
Excessive arc energy melting groove along weld toe; incorrect torch angle or travel speed
Insufficient heat input; incorrect welding parameters; contaminated joint surfaces
PAUT (best — planar defect), TOFD (sizing), RT (less sensitive to planar LOF parallel to beam)
Hydrogen-induced cracking (HAC/HICC), solidification cracking, stress corrosion, fatigue
PAUT/UT (excellent), MT — surface/near-surface, PT — surface only, TOFD — through-wall sizing
RT (excellent for elongated slag lines), PAUT (good), UT conventional (moderate)
Weld metal flowing over base metal without fusion; low current, incorrect torch angle
Structural Welding Code — Steel. Governs weld inspection for structural steel in buildings, bridges, and structures. RT, UT (Annex K for PAUT), MT, PT acceptance criteria.
Welding, Brazing, and Fusing Qualifications. Governs WPS/PQR qualification for pressure-retaining welds (vessels, boilers, piping). Used with Section VIII, B31.1, B31.3.
Welding of Pipelines and Related Facilities. Governs girth weld and fillet weld inspection in oil & gas pipelines. RT, UT, MT, PT procedures and acceptance criteria.
Magnetic particle testing of welds — European/international standard for MT of weld joints. Specifies technique, equipment, and acceptance levels.
Non-destructive testing of welds — Radiographic testing (Part 1: X-rays; Part 2: digital detectors). Governs RT of welds in Europe and international projects.
Nondestructive Examination. Reference code for all NDT methods (RT Art 2, UT Art 4, PT Art 6, MT Art 7, VT Art 9). Specifies technique and procedure requirements.
Pressure vessel welds (API 510/ASME VIII), piping welds (API 570/B31.3), pipeline girth welds (API 1104), storage tank welds (API 653/650). High-consequence service requires 100% volumetric inspection on critical welds.
Boiler tube and drum welds (ASME Section I), turbine component welds, HRSG welds (B31.1). PWHT (post-weld heat treatment) requirements and periodic weld inspection during outages.
Structural airframe welds, engine component welds. NAS-410 certification requirements, AMS specifications. Fluorescent PT and UT critical for aerospace weld acceptance.
Hull structural welds, pressure vessel welds, piping welds. Lloyd's Register, Bureau Veritas, DNV GL classification society requirements. RT common for hull welds.
Structural steel welds per AWS D1.1. High-rise, bridge, and infrastructure welds. CWI (Certified Welding Inspector) required on most projects. UT and MT primary methods.
Weld inspection is the largest single application of NDT — approximately 15% of all industrial NDT by volume