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

PAUT and TOFD weld inspection services

This section is for fabricators, contractors and owner-users who need welds examined with encoded ultrasonics rather than read about. Atlantis NDT performs phased array ultrasonic testing (PAUT) and time-of-flight diffraction (TOFD) on production and in-service welds, either as a replacement for radiography where the governing code allows it or as the volumetric method a specification calls for. Every scan plan and procedure is approved by an ASNT NDT Level III before a probe touches the weld.

Scope of the weld inspection service

We examine full-penetration butt welds in plate and pipe, circumferential and longitudinal seams on pressure vessels, nozzle and branch connections, pipeline girth welds, and complete-joint-penetration groove welds on structural steel. PAUT and TOFD are usually combined on thicker sections: TOFD gives accurate through-wall height of planar flaws and good detection in the weld body, while PAUT sectorial and linear scans cover the fusion faces, the root and the cap regions where TOFD has its near-surface and back-wall dead zones.

Typical engagements are new-construction examination where a code permits ultrasonics in lieu of radiography, repair verification after excavation and re-welding, baseline examination of critical welds before start-up, and in-service examination of welds in cracking-prone service. Where radiography is impractical because of access, schedule, or the need to keep other trades working nearby, encoded ultrasonics is often the method that keeps the job moving.

Scope is defined weld by weld. For each joint we confirm the configuration, thickness, material, bevel, access from one or both sides, surface condition and temperature, then write coverage around those facts. Welds that cannot be fully covered from the available scan surfaces are identified in the scan plan before the examination, not discovered in the report.

Codes and acceptance criteria we work to

The examination technique follows ASME Section V Article 4 (including its phased-array and TOFD appendices) or the equivalent ISO techniques (ISO 13588 for automated phased array and ISO 10863 for TOFD), with ASTM E2700 used where a client specification calls for it. Acceptance is always taken from the construction or in-service code that governs the weld, not from the method standard.

Common acceptance bases are ASME Section VIII Division 1 and 2 where ultrasonic examination is permitted in lieu of radiography, ASME B31.3 for process piping, AWS D1.1 for structural steel, API 1104 for pipeline girth welds, and ISO 19285 or ISO 15626 on projects specified to ISO. Where a client specification adds requirements — tighter sizing tolerances, specific reference reflectors, or witness points — we build them into the procedure and the scan plan. See also our TOFD testing and phased array UT method pages for how each technique behaves.

Deliverables: what the weld inspection report contains

The approved scan plan: probe and wedge selection, focal laws or TOFD probe centre spacing, index offsets and coverage drawings for each weld configuration.
Calibration and sensitivity records, including the reference block identification, the sensitivity settings used and the checks performed during the shift.
Encoded data files in the instrument's native format, so a second reviewer or a later campaign can re-open the original scans.
An indication table per weld: position along the weld, depth, length and through-wall height, characterisation, and accept or reject against the stated criteria.
A weld map or register linking each report to the joint identifiers used on your drawings or weld log.
The procedure and revision used, the technicians' certification levels, and the Level III review of the report.

If a weld is rejected, the report states the governing clause and the measured dimensions so that your repair can be scoped and the repaired weld re-examined to the same procedure.

Mobilisation and coverage

Field work is mobilised within North America; confirm your site location, access requirements and dates in your RFQ and we will tell you what is achievable for that scope. Mobilisation lead time depends on the site's own permitting, induction and safety requirements as much as on our schedule, so we confirm it per job rather than quoting a standard figure.

For work outside North America, send the details anyway; we will say plainly whether we can support it.

Qualifications behind the work

Examinations are performed by technicians certified in ultrasonic testing under an employer written practice to ASNT SNT-TC-1A, working to procedures and scan plans approved by an ASNT NDT Level III. Company founder Anoop Rayavarapu is ASNT NDT Level III and signs the technical review. If your contract requires a specific scheme or client-specific qualification in addition, state it in the RFQ so we can confirm it before award rather than after.

What we need from you

Weld list or weld map with joint identifiers, and drawings showing configuration, thickness and bevel.
Material specification, any cladding or overlay, and whether post-weld heat treatment has been done.
The governing code and edition, the acceptance criteria and any client specification.
Access details: scan surfaces available, cap condition, insulation or coating to be removed, and surface temperature.
Site requirements: inductions, permits, working hours and who will witness.

Frequently asked questions: PAUT and TOFD Weld Inspection Services

Can PAUT or TOFD replace radiography on our welds?

Only where the governing code and your client allow it. ASME Section VIII, ASME B31.3, AWS D1.1 and API 1104 each have their own conditions for using ultrasonics in place of radiography. We confirm the permitted route for your weld before quoting.

Why combine PAUT and TOFD instead of using one of them?

TOFD gives accurate through-wall height and good detection in the weld body but has blind zones near the scan and back-wall surfaces. PAUT covers those regions and the fusion faces. On thicker sections the combination gives coverage that neither gives alone.

Do we receive the raw encoded data?

Yes. The encoded files are part of the deliverable, so you or a third party can re-review them and later campaigns can compare against them.

Who approves the scan plan?

An ASNT NDT Level III approves every scan plan and procedure before examination. If your client also needs to approve it, build that step into the schedule.

Request a quote for paut and tofd weld inspection services or use the RFQ form below. See all inspection services and ASNT Level III consulting.

Request an inspection quote (RFQ)

Tell us the asset, the method, where it is, the governing code, your dates, the size of the job and the report you need. We reply with questions or a quote. Affordable, accessible, fully customizable — no published pricing.

Or email the same details to info@atlantisndt.com. Mobilisation: North America; confirm your location in your RFQ.