This internationally agreed document specifies quality levels of imperfections in fusion-welded joints (except for beam welding). It applies to material thickness ≥ 0,5 mm and covers fully penetrated butt welds and all fillet welds. Its principles can also be applied to partial-penetration butt welds.
Several types of loads are considered, e.g. static load, thermal load, corrosion load, pressure load and additional guidance on fatigue loads is given. The standard covers manual, mechanized and automated welding; all welding positions; and types of weld, e.g. butt welds, fillet welds and branch connections. It also deals with a wide range of welding processes, namely: metal arc welding without gas protection; submerged arc welding; gas-shielded metal arc welding; gas-shielded arc welding with non-consumable tungsten electrodes; plasma arc welding; and for steel only, oxy-fuel gas welding.
The role of imperfection
To answer the original question as to how users evaluate the quality of fusion welded joints: the standard specifies how welds can be assessed on the basis of their imperfections, or more precisely, the dimensions of their imperfections. It asks users to detect, using various non-destructive examination and testing techniques, the physical dimensions of various types of typical weld defect or imperfection. Defects and imperfections can include things like excessive asymmetry, root concavity, microcracks, clustered porosity, lack of penetration, lack of root fusion, excessive or insufficient throat thickness and linear misalignment.
The standard specifies three quality levels (B, C and D – with B being the most stringent) for weld joints. Quality levels refer to production and good workmanship. The dimension of the imperfection dictates into which level the welded joint will be classed.
Universally applicable process control acceptance criteria
The importance of the standard is that when various examination and non-destruction testing techniques are applied – e.g. ultra-sonic, magnetic particle, dye penetrant, X-ray and so on – these are developed from different scientific bases. As a consequence, each has their own independent acceptance criteria based on their own science.
What sets BS EN ISO 5817:2023 apart is that it provides more universally applicable process control acceptance criteria for fusion welded joints. Hence it acts as a means of comparing weld imperfections and defects irrespective of which common inspection technique is used. It thus permits engineers, welders and quality assessors to have a common and easily understood language in relation to fusion weld joint quality that they can apply in discussions, design, execution, inspection, procurement and so on.
This means that execution standards in different sectors can use BS EN ISO 5817:2023 to set criteria for weld acceptance related to production (prior to being in service) by adopting these levels depending on the service conditions that products in those sectors will be exposed to in due course. The sectors can vary from mechanical engineering, pressure equipment, wind energy, and railways to steelwork in construction. For example, BS EN 1090-2 in steelwork relies heavily on BS EN ISO 5817, as does the similar railway standard.
Finally, BS EN ISO 5817:2023 is the latest revision of this standard - there are changes to clauses throughout and updates to Table 1 on Limits for Imperfections. Keen-eyed users will also note that the “old” Annex B has been deleted, promoting the former Annex C on fatigue into the new Annex B. The revision is just to make sure that this well-used standard remains as relevant and useful as ever.