ISO 5817 weld quality levels
The ISO 5817 standard establishes three quality levels for imperfections in fusion-welded joints in materials such as steel, nickel, and titanium. Level B is the most demanding and is applied when structural integrity is critical, while Level D is the most permissive and suitable for applications with lower strength requirements. This classification allows selecting the appropriate inspection grade based on the function of the weld, reducing manufacturing costs without compromising safety.
Operating Parameters
Section titled “Operating Parameters”The imperfection limits depend directly on the weld thickness and the specified quality level. The standard covers surface defects such as cracks, lack of fusion, excessive penetration, and undercuts, as well as internal imperfections detectable by volumetric testing.
| Imperfection | Limit for Level B (thickness 3 mm / 0.12 in) | Limit for Level C (thickness 3 mm / 0.12 in) | Limit for Level D (thickness 3 mm / 0.12 in) |
|---|---|---|---|
| Cracks | Not allowed | Not allowed | Not allowed |
| Lack of fusion | Not allowed | Not allowed | Not allowed |
| Lack of penetration | Not allowed | h ≤ 0.1 mm / 0.004 in, but not allowed for lengths greater than 25 mm / 1 in | h ≤ 0.2 mm / 0.008 in, maximum length 50 mm / 2 in |
| Undercut (h) | h ≤ 0.5 mm / 0.02 in, but only for partial penetration | h ≤ 1.0 mm / 0.04 in, with length limit | h ≤ 1.5 mm / 0.06 in, no length limitation |
| Porosity (individual) | d ≤ 0.3 mm / 0.012 in, maximum 1 per 10 mm / 0.4 in length | d ≤ 0.4 mm / 0.016 in, maximum 2 per 10 mm / 0.4 in length | d ≤ 0.5 mm / 0.02 in, maximum 3 per 10 mm / 0.4 in length |
| Excess penetration | h ≤ 1.0 mm / 0.04 in | h ≤ 2.0 mm / 0.08 in | h ≤ 3.0 mm / 0.12 in |
Tolerances and Defects
Section titled “Tolerances and Defects”The weld defects classified in this standard include dimensional imperfections, bead geometry deviations, and internal discontinuities. Maximum tolerances are expressed as deviations from the ideal shape of the welded joint. Misalignment between parts in a Level B butt weld must not exceed 0.5 mm / 0.02 in for thicknesses up to 10 mm / 0.4 in, while at Level D it can reach 1.5 mm / 0.06 in. Weld bead concavity is limited to 2% of the nominal throat thickness for Level B, 5% for Level C, and 10% for Level D. Solid or slag inclusions must not exceed the material thickness in maximum length at Level B, and may reach up to twice the thickness at Level D if they do not compromise joint continuity.
Applicable Materials
Section titled “Applicable Materials”The standard mainly applies to carbon steels, low-alloy steels, stainless steels, nickel alloys, and titanium alloys. The weldability of these materials varies and must be considered when selecting the quality level.
| Material | General Weldability | Compatibility with Level B | Compatibility with Level C | Compatibility with Level D |
|---|---|---|---|---|
| Carbon and low-alloy steel | Excellent | High | High | High |
| Austenitic stainless steel (e.g., 304, 316) | Excellent | High | High | High |
| Martensitic stainless steel (e.g., 410) | Moderate | Medium | Medium | High |
| Nickel alloys (e.g., Inconel) | Excellent | High | High | High |
| Titanium alloys | Good | High | Medium | Medium |
Advantages and Limitations
Section titled “Advantages and Limitations”The main advantage of the ISO 5817 classification is the objective standardization of weld quality, which facilitates communication between design, manufacturing, and inspection. Reducing the quality level from B to D can lower manufacturing costs by up to 30% due to fewer repairs and shorter inspection times. As a limitation, Level D is not suitable for components subjected to dynamic fatigue, seismic loads, or high cyclic pressures. Additionally, subjective interpretation of some surface defects can lead to discrepancies between inspectors, requiring specific training in ISO 9712 for non-destructive testing.
Selection Guide
Section titled “Selection Guide”The selection of the quality level should be based on component criticality, type of load, and service conditions.
| Application | Recommended Quality Level | Justification |
|---|---|---|
| Pressure vessels (Category IV per PED) | B | Requires maximum structural integrity and fatigue resistance; cracks are not tolerable at any thickness. |
| Building metal structures (static loads) | C | Balance between safety and manufacturing cost; control of moderate undercuts and porosity. |
| Decorative or non-load-bearing enclosure components | D | No significant structural risk; production economy is prioritized. |
| Process piping with non-hazardous fluids | C or D | D is acceptable for low pressure and ambient temperature; C is chosen if there are thermal fluctuations. |
| Stainless steel joints in the food industry | B or C | B for direct product contact; C for supports and chassis, provided cleanliness is not compromised. |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What does it mean for a weld to comply with Level B of ISO 5817?
Section titled “What does it mean for a weld to comply with Level B of ISO 5817?”It meets the strictest acceptance criteria for imperfections, being suitable for high-safety applications such as pressure equipment or structures subjected to fatigue.
Can quality levels be mixed in the same welded joint?
Section titled “Can quality levels be mixed in the same welded joint?”Yes, the same component can have welds with different quality levels, provided the manufacturing drawings clearly indicate the required level for each joint.
Does ISO 5817 apply only to steels?
Section titled “Does ISO 5817 apply only to steels?”No, the standard also covers nickel and titanium alloys. For aluminum and its alloys, the specific standard ISO 10042 is used.
What is the difference between an acceptable undercut at Level C and one at Level D?
Section titled “What is the difference between an acceptable undercut at Level C and one at Level D?”At Level C the undercut must not exceed 1.0 mm / 0.04 in depth and has a maximum cumulative length limited to 25% of the total weld length, while at Level D it can reach 1.5 mm / 0.06 in with no length restriction.
Which defect is not allowed at any quality level?
Section titled “Which defect is not allowed at any quality level?”Cracks and lack of fusion are prohibited for all three quality levels, as they compromise material continuity and mechanical strength.
How does material thickness affect the porosity limit?
Section titled “How does material thickness affect the porosity limit?”At greater thickness, the dimensional limits of individual pores remain fixed, but the allowable frequency is calculated based on weld length, not thickness, so there is no direct relationship.