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Application standards, codes of practice and quality levels Application standards and codes of practice ensure that a structure or component will have an acceptable level of quality and be fit for the intended purpose. Production at Dennis vehicle manufacturers In this document, the requirements for standards on welding procedure and welder approval are explained together with the quality levels for imperfections. It should be noted that the term approval is used in European standards in the context of both testing and documentation. The equivalent term in the ASME standard is qualification. Application standards and codes There are essentially three types of standards which can be referenced in fabrication: Application and design Specification and approval of welding procedures Approval of welders There are also specific standards covering material specifications, consumables, welding equipment and health and safety. British Standards are used to specify the requirements, for example, in approving a welding procedure, they are not a legal requirement but may be cited by the Regulatory Authority as a means of satisfying the law. Health and Safety guidance documents and codes of practice may also recommend standards. Codes of practice differ from standards in that they are intended to give recommendations and guidance, for example, on the validation of power sources for welding. It is not intended that should be used as a mandatory, or contractual, document. Most fabricators will be working to one of the following: Company or industry specific standards National BS (British Standard) European BS EN (British Standard European Standard) US AWS (American Welding Society) and ASME (American Society of Mechanical Engineers) International ISO (International Standards Organisation) Examples of application codes and standards and related welding procedure and welder approval standards are listed in Table 1. Table 1 Examples of application codes and standards and related welding procedure and welder approval standards Welding standard Application Application code/standard Procedure approval Welder approval Pressure vessels BS 5500 ASME VIII BS EN 288 ASME IX BS EN 287 ASME IX Process pipework BS 2633 BS 4677 ANSI/ASME B311 ANSI/ASME B31.3 BS 2971 BS EN 288 (Part 3) BS EN 288 (Part 4) ASME IX ASME IX BS EN 288 (Part 3) (if required) BS EN 287 (Part 1) BS EN 287 (Part 2) ASME IX ASME IX BS 4872/BS EN 287 Structural fabrication AWS D1.1 AWS D1.2 BS 5135 BS 8118 AWS D1.1 AWS D1.2 BS EN 288 (Part 3) BS EN 288 (Part 4) AWS D1.1 AWS D1.2 BS EN 287 BS EN 287 BS 4872 Storage tanks BS 2654 BS 2594 API 620/650 BS EN 288 (Parts 3 & 4) BS EN 288 (Parts 3 & 4) ASME IX BS EN 287 BS EN 287 ASME IX Note 1: Reference should be made to the application codes/standards for any additional requirements to those specified in BS EN 287, BS EN 288 and ASME IX. Note 2: Some BS Standards have not been revised to include the new BS EN standards: BS EN 287 and BS EN 288 should be substituted, as appropriate, for BS 4871 and BS 4870, respectively, which have been with drawn. In European countries, national standards are being replaced by EN standards. However, when there is no equivalent EN standard, the National standard can be used. For example, BS EN 287 replaces BS 4871 but BS 4872 remains as a valid standard. Approval of welding procedures and welders An application standard or code of practice will include requirements or guidelines on material, design of joint, welding process, welding procedure, welder qualification and inspection or may invoke other standards for example for welding procedure and welder approval tests. The manufacturer will normally be required to approve the welding procedure and welder qualification. The difference between a welding procedure approval and a welder qualification test is as follows: The welding procedure approval test is carried out by a competent welder and the quality of the weld is assessed using non-destructive and mechanical testing techniques. The intention is to demonstrate that the proposed welding procedure will produce a welded joint which will satisfy the specified requirements of weld quality and mechanical properties. The welder approval test examines a welder's skill and ability in producing a satisfactory test weld. The test may be performed with or without a qualified welding procedure (note, without an approved welding procedure the welding parameters must be recorded). The requirements for approvals are determined by the relevant application standard or as a condition of contract (Table 1). EN 287 and ASME IX would be appropriate for welders on high quality work such as pressure vessels, pressure vessel piping and off-shore structures and other products where the consequences of failure, stress levels and complexity mean that a high level of welded joint integrity is essential. In less demanding situations, such as small to medium building frames and general light structural and non- structural work, an approved welding procedure may not be necessary. However, to ensure an adequate level of skill, it is recommended that the welder be approved to a less stringent standard e.g. BS 4872. 'Coded welder' is often used to denote an approved welder but the term is not recognised in any of the standards. However, it is used in the workplace to describe those welders whose skill and technical competence have been approved to the requirements of an appropriate standard. Quality acceptance levels for welding procedure and welder approval tests When welding to application standards and codes, consideration must be given to the imperfection acceptance criteria which must be satisfied. Some standards contain an appropriate section relating to the acceptance levels while others make use of a separate standard. For example, in welding procedure and welder approval tests to EN 288 Pt3 and EN 287 Pt1, respectively, reference is made to EN 25817 (ISO 5817). It is important to note that the application standard may specify more stringent imperfection acceptance levels and/or require additional tests to be carried out as part of the welding procedure approval test. For example, for joints which must operate at high temperatures, elevated temperature tensile test may be required whereas for low temperature applications, impact or CTOD tests may be specified. Guidance on permissible levels of imperfections in arc welded joints in steel (thickness range, 3 to 63mm) are given in EN 25817. Production quality, but not fitness-for-purpose, is defined in terms of three levels of quality for imperfections: Moderate - level D Intermediate - level C Stringent - level B The standard applies to most arc welding processes and covers imperfections such as cracks, porosity, inclusions, poor bead geometry, lack of penetration and misalignment. As the quality levels are related to the types of welded joint and not to a particular component, they can be applied to most applications for procedure and welder approval. The quality levels which are the most appropriate for production joints will be determined by the relevant application standard which may cover design considerations, mode of stressing (e.g. static, dynamic), service conditions (e.g. temperature, environment) and consequences of failure. When working to the European Standards, the welding procedure, or the welder, will be qualified if the imperfections in the test piece are within the specified limits of Level B except for excess weld metal, excess convexity, excess throat thickness and excess penetration type imperfections when Level C will apply. Guidance levels for aluminium joints are given in EN 30042. For the American standards ASME IX and AWS D1.1, the acceptance levels are contained in the standard. Application codes may specify more stringent imperfection acceptance levels and/or additional tests. Relevant standards American Welding Society, Structural Welding Code, AWS D1.1 ASME Boiler and Pressure Vessel Code, Section IX: Welding Qualifications BS 4872 Approval Testing of Welders when Welding Procedure Approval is not Required EN 287:1997 Approval Testing of welders for fusion welding EN 288: Specification and approval of welding procedures for metallic materials EN 25817:1992 (ISO 5817) Arc welded joints in steel - Guidance on quality levels for imperfections. EN 26520 Classification of imperfections in metallic fusion welds, with explanations. EN 30042:1994 Arc-welded joints in aluminium and its weldable alloys. Guidance on quality levels for imperfections.