13.1 Visual Testing (ISO 17637)

13.1 Visual Testing (ISO 17637)

Quick Answer: Visual testing (VT) is the first-line NDT for fusion welds. ISO 17637 covers principles for VT of welds—direct inspection (eye, with or without aids) under controlled lighting, viewing distance (commonly within ~600 mm), and viewing angle (commonly ≥30° to the surface). VT finds surface imperfections only; use gauges and rules to measure, not guess.

Chapters 11–12 classified imperfections (ISO 6520) and evaluation logic (ISO 5817 concepts). WI2.3 moves to how the inspector actually looks: visual testing as a formal NDT method, not casual “walk-by looking.” IWI-S candidates supervise VT, perform VT where competent and authorised, and use VT results to decide whether further NDT, repair, or acceptance applies.

Why VT Comes First

Almost every welding ITP starts with visual examination of joint preparation, fit-up, root, intermediate passes (where required), and finished welds. Reasons:

1. Cheap and immediate — no radiation, no coupling medium, no particle media if only VT is required
2. Catches process problems early — undercut, overlap, poor profile, misalignment, incomplete fill, arc strikes, spatter, wrong size
3. Primes other NDT — surface dirt, rough grind marks, and paint hide PT/MT indications; VT confirms readiness
4. Contract and code baseline — many product standards require 100% VT even when RT/UT is sample-based

VT is necessary but not sufficient. A weld that “looks perfect” can still hide subsurface LOF or internal porosity. Never treat a clean VT as a substitute for required volumetric NDT.

ISO 17637 — Role and Scope

ISO 17637 (Non-destructive testing of welds — Visual testing of fusion-welded joints) gives general principles for personnel who perform VT of fusion welds. It does not replace the acceptance standard (e.g. ISO 5817, application standard, or client spec). Think of it as the how to look document; ISO 5817 (or equivalent) is the how to judge document.

Typical content themes IWI-S must internalise:

Always apply the edition cited in the contract and any national annexes or company procedures that tighten ISO 17637.

Direct VT: Unaided and Aided

Direct visual testing means the inspector’s eye (with normal vision corrected by spectacles/contact lenses if needed) views the surface—either unaided or aided.

Unaided direct VT

Unaided means no optical magnification beyond normal corrective lenses. Most shop VT of accessible faces is unaided: face of fillet, cap of butt, accessible root of open pipe, edge preparations. Vision acuity requirements are usually set by the NDT personnel qualification system (e.g. ISO 9712 vision rules applied by the employer’s written practice) or company procedure—not invented on the shop floor.

Aided direct VT

Aids improve access or detail without turning the method into remote camera inspection:

• Mirrors — reverse side of plates, inside corners, pipe roots from an access hole
• Magnifiers / low-power loupes — local detail of toe cracks, porosity pits, undercut depth assessment (still measure with a gauge)
• Boroscopes / fibrescopes / video borescopes — internal pipe, vessels, box sections (procedure may class these as direct-aided or as a defined remote method—follow the written practice)
• Portable lights — to reach the lux level in dark vessels or night shifts

Remote visual testing (fixed cameras, robotic crawlers) is a related discipline with its own procedure controls (resolution, recording, lighting calibration). For Standard-level exam focus, master direct VT principles first; know that remote systems need qualified procedures and do not automatically equal a hand-held VT pass.

Lighting — Commonly ≥350 lux

You cannot accept or reject what you cannot illuminate. Practice, many company VT procedures, and inspection meta guidance commonly cite a minimum surface illuminance of about 350 lux (sometimes higher for fine work). Key points:

• Lux measures luminous flux per unit area on the surface—not “how bright the hall lights feel”
• Measure or verify with a light meter when the procedure requires it, or when access areas are dim (tanks, night yards, under scaffolding)
• Glare and strong shadows can hide undercut and fine cracks; reposition lights rather than squinting
• Supplemental white LED hand lamps are normal tools; coloured lighting can distort colour contrast of rust, dye, or paint—prefer neutral white for general VT

Exam trap: memorising “350 lux” without knowing why fails scenario questions. The number is a minimum practical lighting criterion often written into procedures aligned with ISO 17637 principles—not a substitute for accessibility, angle, and cleanliness.

Viewing Distance and Angle

Two geometry rules appear repeatedly in VT training and procedures:

Implications for the inspector:

• Climb, crawl, or use platforms so your eye is close enough—do not “VT from the aisle” on critical welds
• For vertical and overhead welds, plan access so angle ≥30° is achievable on both toes of a fillet
• Use a mirror when body position cannot meet angle/distance; document aided VT if the procedure requires it
• Photograph only as a record aid—photos do not replace meeting distance/angle unless a remote VT procedure is qualified

Surface Condition Before VT

VT of dirty, heavily scaled, or freshly painted surfaces is unreliable:

• Loose slag, spatter, and grinding dust hide toes and cracks—clean sufficiently for the examination stage (without removing required evidence before recording if an NCR is open)
• Heavy mill scale or thick coating may need removal where the ITP requires “bare metal VT” of the weld and adjacent zone
• Paint or primer after welding can mask surface cracks; if final VT is required before coating, enforce the hold point
• Grinding can smear metal over a crack (especially on stainless and soft materials)—inspect before aggressive blend if cracking is suspected

The width of examination usually includes the weld metal plus a defined band of parent metal on each side (procedure/ITP/code)—not only the weld face centreline.

Measuring Tools — From “Looks Bad” to Data

IWI-S work demands quantified observations:

Rule: if ISO 5817 or the product standard gives a millimetre limit, measure it. Eye estimates fail audits and oral exams.

Examination Stages Linked to the Weld Lifecycle

1. Materials and preparation — square edges, bevel angle, root face, cleanliness, correct material marks
2. Fit-up — gap, alignment, tacking quality, root opening consistency
3. In-process (when ITP requires) — root pass, hot pass, interpass cleanliness, layer sequence
4. Final VT — finished size, profile, undercut, overlap, cracks open to surface, spatter, arc strikes, dimensional compliance
5. After repair / after PWHT / after pressure test — as specified; PWHT can open previously tight surface cracks—re-VT when required

Limitations of VT (Critical Exam Points)

Open-to-surface discontinuities that are extremely tight may still be missed by VT alone—hence PT or MT when the risk or code requires higher surface sensitivity.

Inspector Competence and Reporting

• VT personnel should be trained and authorised under the employer’s written practice / ISO 9712 scheme as applicable; IWI-S supervises, verifies conditions, and challenges weak reports
• Reports state identity of item, procedure/standard, stage, extent (100% / sample), lighting/access notes if required, results, accept/reject against named acceptance standard, inspector ID and date
• Photographs and sketches support NCRs but do not replace measurements

Link Forward

When VT is insufficient for surface-breaking crack sensitivity, liquid penetrant (13.2) and magnetic particle (13.3) extend surface NDT. Volumetric methods (Chapter 14) address the interior. Selection among them is a core IWI-S skill under WI2.

High-Yield VT Checklist

1. Confirm acceptance standard and examination stage on the ITP
2. Verify access, cleanliness, ≥350 lux class lighting (or procedure value), ≤~600 mm viewing distance, ≥~30° angle
3. Inspect weld and adjacent parent band; both toes; root if accessible
4. Measure size and imperfections; compare to limits
5. Record results; raise NCR or release hold point with evidence
6. Do not close VT as “OK for all NDT needs” if RT/UT/PT/MT remain on the plan