Now that CE marking of structural steelwork and aluminium structures is mandatory it may be an appropriate time to look at some of the fabrication requirements within the specification, BS EN 1090 Part 2, that must be complied with in order to be able to apply a CE mark. It is suggested that Job Knowledge No. 120 – Structural Steel, CE Marking and ISO 3834 should be read in conjunction with this article. It should also be noted that no brief article such as this Job Knowledge article can cover every aspect of a specification requirement - the specification itself must be referred to for accuracy.
Part 1 of the BS EN 1090 series specifies the requirements for conformity assessment of what are termed the performance characteristics of the structure – essentially those criteria such as toughness, fire resistance, fatigue performance etc – and requires the implementation of a factory production control (FPC) system – see Job Knowledge No. 120 for further information. BS EN 1090 Part 2 is entitled “Technical requirements for the execution of steel structures” and specifies the requirements for the manufacturing of structural steelwork - this includes both bolting and welding. The steels covered by the specification comprise not only the conventional carbon manganese steels such as EN 10025 S275 but also high strength steels up to grade S960, ferritic, austenitic-ferritic and austenitic steels.
This article will not cover what may be termed the conventional requirements for welding such as procedure qualification, welder qualification, welding plan requirements etc but will attempt to highlight those requirements that may not be normal practice within the fabrication shop. There are several clauses within the specification that may cause some difficulties if the requirements are strictly enforced and no concessions are permitted. For example clause 5.5 states that all welding consumables shallcomply with EN 13479, the general product standard for filler metals and fluxes – the term “shall” makes this mandatory and consumables complying with other specifications only, the AWS standards for example, cannot be used. The same does not apply to parent materials where specifications other than the European material specifications can be used “....if otherwise specified...”
The quality of cut edges is dealt with in clause 6.4. This requires that any ‘free’ cut edge, but not weld preparations, complies with limits on tolerance, hardness and smoothness. A footnote states that hand thermal cutting should only be used if it is not practical to use machine thermal cutting. If specified in the contract documentation thermally cut edge hardness shall not exceed 380HV10 for hot finished or normalised S235 to S460 steels and 450HV10 for cold forming or quenched and tempered S260 to S700 steels. Although this requirement may not be mandatory for all contracts it would be advisable to produce a qualification test record to demonstrate compliance. The clause also requires that the “...capability of thermal cutting processes shall be periodically checked....”. The period between checks is not specified. The checks comprise the production of four samples, one each from the thickest and thinnest product and one each from a sharp corner and a curved cut from products of representative thickness. Records of such periodic checks should be maintained for audit purposes.
Clause 6.5 is entitled ‘Shaping’ and permits hot and cold forming and flame straightening “....provided the properties are not reduced below those specified for the worked material...” and calls up the guidance given in TR 10347 ‘Guidance for forming of structural steels in processing’. For many structural steel fabrication companies, hot and cold forming is sub-contracted to specialist benders; these must supply the fabricator with documentary evidence that the properties have not been reduced below those specified for inclusion in the as-built QA documentation pack. Flame straightening, however, may be carried out by the fabricator and, for EXC3 and EXC4, a written procedure is required that details the maximum temperature, method of heating, workers permitted to use the process and the results of mechanical tests carried out for the process approval. A procedure qualification record (PQR), similar to that of a welding PQR, is therefore required.
Clause 7 covers the welding requirements, most of which are relatively conventional but there are some additional requirements that need to be taken into account as follows:
- Cl 126.96.36.199.b(3) requires procedure qualification tests to be carried out on test pieces with the maximum prefabrication primer thickness if welding is carried out over shop primers. This would need recording on the PQ certificate.
- Cl 188.8.131.52.c. Transverse stressed fillet welds in steels of a higher grade than S275 and with a fillet weld throat less than half the component thickness need an additional cruciform test piece to be welded and three tensile tests performed.
- Table 12 permits EXC 2 welding procedures to be qualified in accordance with ISO 15614-1, ISO 15613, ISO 15612 (standard welding procedure), ISO 15611 (previous welding experience) and ISO 15610 ( tested welding consumables). EXC 3 and EXC 4 must be qualified to either ISO 15614-1 or ISO 15613.
- Cl 184.108.40.206 requires some additional testing to be performed if a welding process with a relevant PQR has not been used for a period of time –i) between one and three years a production weld test is required to weld steel grades greater than S355 ii) over three years for steels ≤S355 a macro-section is to be taken and for steels>S355 a new procedure qualification test is required.
- Cl 7.4.2 Welders must be specifically qualified to weld hollow section branches with an angle less than 60O.
- Table 16 requires electrode quivers to be heated to 100°C minimum rather than the 75°C that is generally used.
- Cl 7.5.5 requires tack welds and temporary attachments to be preheated in accordance with the relevant welding procedure specification.
- Cl 7.5.6 covers the requirements for temporary attachments which may be attached in accordance with a written welding procedure. Cutting or chipping of temporary attachments is not permitted for EXC3 and EXC4 components unless otherwise specified. It is not clear if cutting refers to thermal cutting and if this is permitted if the cut surface is clear of the component surface, say by a minimum of 3mm which is normal practice. It is recommended that an attachment removal method statement is written and implemented on the shop floor to remove doubt.
- Cl 7.5.7 covers the requirements for the qualification of tack welds, a topic that is being interpreted differently by various companies. Tack welds on EXC2, EXC3 and EXC4 components are required to be welded in accordance with a qualified WPS. Tack welds are to be a maximum length of 4x the thickness of the thicker part or 50mm “...unless a shorter length can be demonstrated as satisfactory...”. Unfortunately the clause does not define what is “satisfactory” so this is left to individual interpretation. Tack welds that are to be incorporated into the completed weld can be qualified by ensuring that the lengths and positions of the tack welds on the qualification test piece are marked and at least one macro-section is taken through the tack and hardness tested. This would need to be noted in the procedure qualification record. The major issue concerns the qualification of small temporary tack welds that may be used, for example, to tack weld a thin wall small diameter bracing to a large thick beam. How such a tack weld is to be qualified is not clear and has yet to be resolved.
- Cl 7.5.9 deals with butt welds and Cl 220.127.116.11 specifies that the ends of butt welds shall be terminated in a manner that ensures sound welds. For EXC3 and EXC4 and EXC2, if specified, this shall be achieved by the use of run on/off plates that will be later removed.
- Cl 18.104.22.168 covers single sided butt welds. Tack welds shall be included in the final weld and permanent or removable backing may be used. For EXC3 and EXC4 this backing shall be continuous for the full length of the joint, if necessary by joining the backing lengths together by full penetration butt welds. Note, however, that many contract specifications are prohibiting the use of backing for EXC3 and EXC4 components and specifying that the welds shall be full penetration unbacked joints.
- Cl 22.214.171.124. This clause is entitled scope of inspection and is relatively straightforward – there is just one requirement that needs to be mentioned. This is that the first five joints made to the same new WPS require inspecting to twice the extent specified in Table 24 and to an EN 5817 acceptance level of Quality Level B. The reason for this additional testing is to establish that the new WPS can provide the required quality in production – as distinct from that which can be provided during procedure qualification testing.
Specific industry standards are being developed which, although based on BS EN 1090 Part 2, will contain additional requirements that may mean further qualification testing will be needed. Once such specifications are available then these may form part of a Job Knowledge article covering the key differences and additional requirements.