Search common weld imperfections and review acceptance-reference guidance by standard and inspection method.
The search database is intentionally written as a practical reference rather than reproducing copyrighted standards or pretending that one generic numerical limit applies to every weld.
Weld acceptance is the determination of whether an inspected weld satisfies the requirements established for the particular fabrication.
Those requirements can come from a welding code, product standard, contract specification, engineering drawing, welding procedure or other governing document.
A visible indication does not automatically mean that a weld must be rejected. The relevant question is whether the indication meets the applicable acceptance criteria.
The same type of indication can have different acceptance requirements depending on the governing standard and application.
AWS currently lists AWS D1.1/D1.1M:2025-AMD1 as its current amended structural steel welding code. AWS describes D1.1 as covering essential requirements for structural-steel welding, including fabrication, qualification and inspection. 1
For ISO-based inspection, ISO 5817:2023 is the current published edition. It defines three quality levels, B, C and D, with B representing the highest finished-weld requirement. It covers fusion-welded joints in steel, nickel, titanium and their alloys and includes butt and fillet welds. 2
The older ISO 5817:2014 edition is withdrawn and has been replaced by ISO 5817:2023. 3
| Indication | Typical Description | Common Detection | Acceptance Approach |
|---|---|---|---|
| Crack | Linear fracture or crack-like separation in weld metal or adjacent material. | VT, PT, MT, UT, RT depending on location and application. | Generally treated as a serious indication; acceptance depends on the governing specification. |
| Porosity | Gas cavities or pores within or at the surface of the weld. | VT, RT, UT and surface methods depending on geometry. | Often evaluated by size, distribution, number and location rather than by the word "porosity" alone. |
| Undercut | Groove or reduction at the weld toe or adjacent base metal. | Primarily VT; dimensional gauges may be used. | Usually evaluated by depth, length, location and governing code. |
| Overlap | Weld metal extending beyond the toe without proper fusion to the base metal. | VT. | Usually evaluated as a profile/fusion condition against the applicable workmanship requirements. |
| Incomplete fusion | Failure of weld metal to properly fuse with base metal or another weld layer. | VT in accessible cases; UT or RT may be required. | Acceptance depends strongly on the applicable code and examination method. |
| Incomplete penetration | Insufficient penetration through the intended joint thickness or root. | VT where visible; RT or UT where applicable. | Evaluated against required joint penetration and applicable acceptance criteria. |
| Arc strike | Localized unintended arc contact outside the intended weld area. | VT. | Often requires evaluation, removal or repair according to the governing specification. |
| Crater | Depression or discontinuity at the termination of a weld. | VT. | Evaluated according to weld termination and profile requirements. |
| Burn-through | Excessive penetration resulting in a hole or severe root collapse. | VT, RT or other suitable examination. | Acceptance depends on joint design and governing requirements. |
| Spatter | Unfused droplets deposited adjacent to the weld. | VT. | Usually assessed against workmanship, service and project requirements. |
ISO 5817:2023 establishes three quality levels for imperfections in applicable fusion-welded joints. 4
| Level | General Meaning |
|---|---|
| B | Highest quality requirement among the three ISO 5817 levels. |
| C | Intermediate quality requirement. |
| D | Lower quality requirement among the three levels. |
The actual permissible dimensions depend on the specific imperfection category and the relevant ISO 5817 requirements. The quality level should therefore not be treated as a universal pass/fail number.
Visual testing is often the first inspection method because many surface conditions can be identified directly.
However, visual inspection cannot establish the absence of internal discontinuities. Depending on the joint and governing requirements, additional non-destructive testing may include PT, MT, UT or RT.
| Method | Primary Use | Typical Limit |
|---|---|---|
| VT | Surface profile, dimensions and visible indications. | Cannot directly reveal most internal discontinuities. |
| PT | Surface-breaking discontinuities on suitable non-porous materials. | Does not reveal buried internal indications. |
| MT | Surface and near-surface indications in suitable ferromagnetic materials. | Not suitable for non-ferromagnetic materials. |
| UT | Internal discontinuities and weld integrity in suitable configurations. | Requires suitable geometry, calibration and qualified technique. |
| RT | Internal volumetric indications and weld imaging. | Technique, geometry and radiation-safety requirements apply. |
Cracks are among the most serious weld indications because they can represent a significant structural or service-life concern.
When a crack is identified, the inspector should not rely on a generic numerical tolerance from this tool. The applicable code, drawing, specification and repair procedure must be checked.
Porosity consists of gas cavities within or at the surface of a weld. Its acceptance is commonly related to factors such as individual pore size, distribution, concentration and location.
Radiographic inspection can reveal internal porosity that cannot be confirmed through ordinary visual inspection.
For ISO-based work, the applicable ISO 5817 quality level determines the relevant imperfection requirements. 5
Undercut is a groove or reduction in the base metal adjacent to the weld toe or, in some configurations, the weld root.
Inspection normally considers its measured depth and extent rather than merely recording "undercut present."
Because allowable dimensions vary by standard and quality level, an inspector should compare the measured indication with the governing acceptance table rather than use a universal limit.
Incomplete fusion occurs when the weld metal does not properly fuse with the base metal or a previous weld layer.
Some instances may be visible, while others require volumetric examination. The applicable acceptance requirements depend on the joint, code and inspection method.
This is an important example of why an inspection-method filter is useful: a VT result and a UT result are not interchangeable.
A useful inspection record normally considers several pieces of information:
First identify the indication. Then measure the relevant characteristic, such as length, depth, size or distribution. Select the governing standard and the applicable acceptance level. Finally compare the measured condition against the actual requirement.
This workflow is safer than making an acceptance decision based solely on the name of the defect.
This tool is a searchable educational and inspection-reference aid. It does not reproduce complete proprietary acceptance tables from AWS, ISO or other standards.
Acceptance criteria can change with the governing code, edition, weld type, material, thickness, service condition, examination method and project specification.
For structural steel, AWS currently identifies D1.1/D1.1M:2025-AMD1 as an available current edition. 6 For ISO 5817 work, ISO identifies the 2023 edition as the current published edition. 7
What is weld acceptance? Weld acceptance is the determination of whether an inspected weld satisfies the applicable code, drawing, specification or project requirements.
Is every weld discontinuity a defect? No. A discontinuity becomes rejectable when it exceeds the acceptance requirements applicable to the weld.
What standard does ISO use for weld imperfections? ISO 5817:2023 specifies quality levels for imperfections in applicable fusion-welded joints and defines levels B, C and D. 8
What is the current AWS structural steel welding code? AWS currently lists AWS D1.1/D1.1M:2025-AMD1. 9
Can visual inspection detect all weld defects? No. Internal discontinuities can require volumetric NDT such as UT or RT.
Are cracks normally treated seriously? Yes. Cracks are generally a serious indication, but the final disposition must be based on the applicable governing requirements.
Can I use ISO 5817 acceptance criteria for an AWS D1.1 job? Not automatically. The governing project/code requirements determine which acceptance criteria apply.
Does the same porosity limit apply to every weld? No. Acceptance can depend on the standard, quality level, weld type, inspection method and other requirements.
Can this tool replace an NDT inspector? No. It is a reference utility and does not replace qualified inspection personnel, approved procedures or the governing standard.
What should I do when an indication exceeds the acceptance limit? Follow the applicable nonconformance, repair and reinspection procedure. Do not automatically grind, weld or repair a production weld without the required approval and procedure.