ISO 6520-1 ref. 1001
Microcrack
ISO 6520-1 reference 1001 is a crack visible only under magnification, in weld metal, HAZ or parent material. Cause matrix, why standard production NDT alone can miss it, and where acceptance is set.
Reference library
Weld imperfections, indexed by ISO 6520-1 reference
ISO 6520-1 classifies and numbers every weld imperfection, and the acceptance standards are indexed by those numbers rather than by shop-floor names. Each card carries the designation, a cause matrix, a detection matrix saying which inspection families find the imperfection and which cannot, and a pointer to the document that sets the acceptance criteria. The criteria themselves stay in the standard you hold.
Group 1 — Cracks
ISO 6520-1 ref. 101
Longitudinal crack
ISO 6520-1 reference 101 covers cracks running parallel to the weld axis, most often a solidification crack. Cause matrix, why detection depends on whether it breaks the surface, and where acceptance is set.
ISO 6520-1 ref. 102
Transverse crack
ISO 6520-1 reference 102 covers cracks running across the weld axis, produced by restraint or by delayed hydrogen cracking. Cause matrix, why a delayed-inspection interval matters, and where acceptance is set.
ISO 6520-1 ref. 103
Radiating crack
ISO 6520-1 reference 103 is a set of cracks radiating outward from one shared origin point, typically a hard or embrittled spot. Cause matrix, the rule that tells it apart from a branching crack, and where acceptance is set.
ISO 6520-1 ref. 104
Crater crack
ISO 6520-1 reference 104 is the crack that forms in an unfilled weld crater at arc stop. Cause matrix, why crater-fill technique is the real control, and where acceptance is set.
ISO 6520-1 ref. 105
Group of disconnected cracks
ISO 6520-1 reference 105 is several separate cracks in the same region that share no common point of origin and do not connect. Cause matrix, the rule that tells the group apart from a single crack, and where acceptance is set.
ISO 6520-1 ref. 106
Branching crack
ISO 6520-1 reference 106 is a primary crack that has split into connected branches from a shared origin. Cause matrix, why sizing is the real challenge, and where acceptance is set.
Group 2 — Cavities
ISO 6520-1 ref. 2011
Gas pore
ISO 6520-1 reference 2011 covers the single gas pore. Cause matrix, which inspection route actually finds it, and the standards that set the acceptance limit for your material and code.
ISO 6520-1 ref. 2012
Uniformly distributed porosity
ISO 6520-1 reference 2012 is gas porosity spread evenly through the weld metal rather than concentrated at one point. Cause matrix, why radiography defines the pattern, and where acceptance is set.
ISO 6520-1 ref. 2013
Clustered porosity
ISO 6520-1 reference 2013 is a localized group of gas pores rather than an even scatter. Cause matrix, the local process upset that produces a cluster, and where acceptance is set.
ISO 6520-1 ref. 2014
Linear porosity
ISO 6520-1 reference 2014 is gas pores aligned in a row along the weld axis, easy to mistake for a planar flaw on a radiograph. Cause matrix, detection routes, and where acceptance is set.
ISO 6520-1 ref. 2015
Elongated cavity
ISO 6520-1 reference 2015 is a non-tubular gas cavity stretched along the weld axis, distinct from a wormhole's tubular form. Cause matrix, the shape rule that tells the two apart, and where acceptance is set.
ISO 6520-1 ref. 2016
Wormhole
ISO 6520-1 reference 2016 is an elongated, tunnel-shaped gas cavity, common wherever flux or shielding carries moisture. Cause matrix, why radiography reads its signature, and where acceptance is set.
ISO 6520-1 ref. 2017
Surface pore
ISO 6520-1 reference 2017 is a gas pore that breaks the weld surface, the one porosity designation visual testing actually leads on. Cause matrix, detection routes, and where acceptance is set.
ISO 6520-1 ref. 202
Shrinkage cavity
ISO 6520-1 reference 202 is a cavity formed by volumetric contraction on solidification, not by trapped gas. Cause matrix, why radiography reads the two differently, and where acceptance is set.
ISO 6520-1 ref. 2024
Crater pipe
ISO 6520-1 reference 2024 is a shrinkage cavity at the arc-stop point, from insufficient crater fill. Cause matrix, why it shares a location with crater cracking, and where acceptance is set.
Group 3 — Solid inclusions
ISO 6520-1 ref. 301
Slag inclusion
ISO 6520-1 reference 301 is trapped slag left behind by a flux-shielded process. Cause matrix, why radiography leads the detection routes, and the standards that govern acceptance.
ISO 6520-1 ref. 302
Flux inclusion
ISO 6520-1 reference 302 is unfused flux carried into the weld metal, distinct from the fused slag of reference 301. Cause matrix, the test that tells them apart, and where acceptance is set.
ISO 6520-1 ref. 303
Oxide inclusion
ISO 6520-1 reference 303 is trapped metallic oxide, most often the tenacious oxide film aluminium forms in air. Cause matrix, the shop-floor rule that flags it fast, and where acceptance is set.
ISO 6520-1 ref. 3041
Tungsten inclusion
ISO 6520-1 reference 3041 is a fragment of electrode shed into the pool during GTAW. Cause matrix, why radiography reads it with unusual clarity, and the standards that govern acceptance.
ISO 6520-1 ref. 3042
Copper inclusion
ISO 6520-1 reference 3042 is a fragment of copper shed from equipment into the weld pool, not the electrode. Cause matrix, the decision rule that points at the source, and where acceptance is set.
Group 4 — Lack of fusion and penetration
ISO 6520-1 ref. 401
Incomplete fusion
ISO 6520-1 reference 401 is a planar imperfection that visual inspection cannot see. Cause matrix, why ultrasonic testing leads the detection routes, and the standards that govern acceptance.
ISO 6520-1 ref. 4011
Sidewall lack of fusion
ISO 6520-1 reference 4011 is a planar imperfection at the joint bevel face that visual inspection cannot see. Cause matrix, why ultrasonic testing leads detection, and the standards that govern acceptance.
ISO 6520-1 ref. 4012
Lack of inter-run fusion
ISO 6520-1 reference 4012 is a planar imperfection between passes in a multi-pass weld, distinct from sidewall and root fusion failures. Cause matrix, the geometry test that locates it, and where acceptance is set.
ISO 6520-1 ref. 4013
Root lack of fusion
ISO 6520-1 reference 4013 is a planar imperfection at the root of the joint, buried the moment the fill passes go on. Cause matrix, detection routes, and the standards that govern acceptance.
ISO 6520-1 ref. 402
Incomplete penetration
ISO 6520-1 reference 402 is a shortfall in the depth the weld metal actually reaches at the root. Cause matrix, why radiography leads detection, and the standards that govern acceptance.
ISO 6520-1 ref. 4021
Incomplete root penetration
ISO 6520-1 reference 4021 narrows lack of penetration to the single-side butt weld, welded from one side only. Cause matrix, the configuration that separates it from reference 402, and where acceptance is set.
Group 5 — Imperfect shape and dimension
ISO 6520-1 ref. 5011
Undercut
ISO 6520-1 reference 5011 is a surface groove at the weld toe and a fatigue initiation site. Cause matrix, why visual testing leads here, and the standards that set the acceptance limit.
ISO 6520-1 ref. 5013
Shrinkage groove
ISO 6520-1 reference 5013 is undercut's root-side member (501), formed by shrinkage rather than arc erosion. Cause matrix, the root-concavity distinction, and where acceptance is set.
ISO 6520-1 ref. 502
Excess reinforcement
ISO 6520-1 reference 502 covers excess weld metal, reinforcement piled above the joint face. Cause matrix, why visual inspection leads, and the standards that set the acceptance limit for your material and code.
ISO 6520-1 ref. 503
Excessive convexity
ISO 6520-1 reference 503 covers excessive convexity, a fillet weld face bulging past its theoretical flat profile. Cause matrix, why the extra metal outside that profile buys no throat, and where acceptance is set.
ISO 6520-1 ref. 504
Excessive penetration
ISO 6520-1 reference 504 covers excess penetration at the weld root. Cause matrix, why radiography leads when the root cannot be seen, and the standards that set the acceptance limit for your material and code.
ISO 6520-1 ref. 505
Incorrect weld toe
ISO 6520-1 reference 505 covers incorrect weld toe: 5051 (angle) and 5052 (radius), an abrupt bead-to-plate transition rather than a smooth blend. Cause matrix, why the pool camera catches poor wetting live, and where acceptance is set.
ISO 6520-1 ref. 506
Overlap
ISO 6520-1 reference 506 covers overlap, weld metal folded over the joint face without fusing to it. Cause matrix, why the fold hides a fusion problem underneath, and the standards that set the acceptance limit for your material and code.
ISO 6520-1 ref. 507
Linear misalignment
ISO 6520-1 reference 507 covers linear misalignment between welded members. Cause matrix, why direct measurement leads over any inspection method, and the standards that set the acceptance limit for your material and code.
ISO 6520-1 ref. 508
Angular misalignment
ISO 6520-1 reference 508 covers angular misalignment, welded members meeting at an unintended angle rather than an offset. Cause matrix, why it is measured in degrees rather than millimetres, and where acceptance is set.
ISO 6520-1 ref. 509
Sagging
ISO 6520-1 reference 509 covers sagging, a weld pool drooping under gravity into an asymmetric profile. Cause matrix, why the pool camera catches it before it freezes, and where acceptance is set.
ISO 6520-1 ref. 510
Burn-through
ISO 6520-1 reference 510 covers burn-through, collapse of the weld pool through the joint. Cause matrix, the thermal precursor that lets you stop it before it happens, and the standards that govern acceptance.
ISO 6520-1 ref. 511
Incompletely filled groove
ISO 6520-1 reference 511 covers incompletely filled groove, a cap or fill pass that stops short of the parent-metal surface. Cause matrix, why a profile gauge settles it, and the standards that set the acceptance limit.
ISO 6520-1 ref. 515
Root concavity
ISO 6520-1 reference 515 covers root concavity, a sagged root bead that has drawn inward as it froze. Cause matrix, why backing gas purge is the leading control, and the standards that set the acceptance limit.
ISO 6520-1 ref. 517
Poor restart
ISO 6520-1 reference 517 covers poor restart, a flaw at the point welding resumes after a stop. Cause matrix, why the location is known in advance, and the standards setting the acceptance limit.
Group 6 — Miscellaneous imperfections
ISO 6520-1 ref. 601
Arc strike
ISO 6520-1 reference 601 covers arc strike, accidental arc initiation on parent material outside the joint. Cause matrix, why the surrounding surface needs its own sweep, and the standards treating it as a defect.
ISO 6520-1 ref. 602
Spatter
ISO 6520-1 reference 602 covers spatter, molten metal ejected from the arc that lands outside the weld. Cause matrix, why a rising rate signals arc instability, and the standards treating it as a surface condition.
Find the condition while the arc is still running
Nearly every imperfection on these pages is produced by conditions that exist during welding. Therness records those conditions on every weld, so a suspect run is known before the part moves on.
