Chapter 14
Standardization: Organization and Quality Control in Welding 1
14.1. Introduction
The manufacture of assemblies or welded constructions has for many years been the object of statutory texts or standardization. The field of pressure vessels has been covered by a code for about 30 years, while the French standards of the P 22 series, relating to steel construction, were established from 1975 onwards. Similarly, assemblies fabricated by welding are dealt with in the five parts of the French standard NF E 83-100 “Construction of fabricated assemblies — welding processes” published at the end of the 1980s and revised in 1995.
Coming into effect in 1987, the European Directive “Simple pressure vessels”, followed by the more recent “unfired pressure vessels”, involved the drafting and adoption of standards developed by the Technical Committee CEN/TC 121 “Welding”, standards which aimed to replace the existing national standardization corpora.
It is not an easy matter to analyze these European standards in so far as they are not completely stabilized and, for various reasons, are subject to revision which will result in a significant modification of their structure. However, the work is sufficiently advanced for general themes to be discussed and the main thread concerning their application to be explained.
Three subjects are thus developed hereafter:
– standards for general organization of quality;
– standards for qualification of procedures or personnel;
– standards relating to non-destructive testing.
14.2. Standards of general organization of quality
14.2.1. Presentation
The general organization of quality requirements for welding was first of all the subject of the European standard NF EN 729 “Quality requirements for welding — fusion welding of metallic materials” in four parts, published in November 1994, as well as a technical report CEN (CR 13576) “Welding — application of the EN 729 quality requirements for the fusion welding of metallic materials” aiming to clarify its proscribed objectives and implementation methods.
This European standard was taken up at an international level under the reference ISO 3834 and its revision in order to ensure a perfect coherence with the new version of the ISO 9000 standards, carried out within the framework of the Vienna agreement, led in April 2006 to the publication of EN ISO 3834 “Quality requirements for fusion welding of metallic materials” in five parts:
– Part 1: Criteria for the selection of the appropriate level of quality requirements.
– Part 2: Comprehensive quality requirements.
– Part 3: Standard quality requirements.
– Part 4: Elementary quality requirements.
– Part 5: Documents with which it is necessary to conform with to meet the quality requirements of ISO 3834-2, ISO 3834-3 or ISO 3834-4.
These five parts were accompanied, as was the case for EN 729, by a technical report ISO/TR 3834-6 “Guidelines on implementing ISO 3834”.
14.2.2. Principles
The key to interpreting this series of standards relating to quality in welding is found in the introduction of ISO 3834-1 “Criteria for the selection of the appropriate level of quality requirements” which specifies: “The specification of quality requirements for welding processes is important because the quality of these processes cannot be readily verified. For this reason they are considered to be special processes as noted by ISO 9000: 2000. Quality cannot be inspected into a product, it has to be built-in. Even the most extensive and sophisticated non-destructive testing does not improve the quality of the product.” This appears self-evident and does not only concern welding, but there are obvious points which it is a good idea to bear in mind sometimes.
On this basis, ISO 3834 covers, in Parts 2, 3 and 4 decreasing in strictness, the quality requirements applicable to welding, both in the workshop and on-site, Part 1 giving the elements of choice according to the contractual requirements using a brief comparison of the requirements. These indications are supplemented in the ISO 3834-6 technical report by Figure 14.1 which follows.
As Parts 3 and 4 only represent restrictions of Part 2, “Comprehensive requirements of quality”, we will restrict ourselves to analyzing the latter by highlighting particular points.
14.2.3. Analysis
The clause giving an overview of ISO 3834 defines the objectives of the standard as follows:
– to be independent of the type of construction manufactured;
– to define welding quality requirements for welding in workshops and/or on-site;
– to provide guidance describing a manufacturer’s capability to produce constructions to meet specified requirements;
– to provide a basis for assessing a manufacturer’s welding capacity.
It is clearly seen that this standard can be used for several purposes. It can be used as a reference in a contract, but also as a tool for the organization of welding quality, as the synopsis of the clauses taken from the ISO 9000 requirements attests by applying them to the particular welding field:
– review of requirements and technical review,
– subcontracting,
– welding personnel,
– inspection and testing personnel,
– equipment,
– welding and related activities,
– welding consumables,
– storage of parent materials,
– post-weld heat treatment,
– inspection and testing,
– non-conformance and corrective actions,
– calibration and validation of measuring, inspection and testing equipment,
– identification and traceability,
– quality records.
Some of these clauses do not need to be commented on because they are traditional and only contain technical elements specifying the application modes of welding operations. Such are the demands relating to the review of requirements and technical review (review of contract), to subcontracting, to the equipment, to welding consumables, to the storage of parent materials, to post-welding heat treatment, to non-conformance and corrective actions, to calibration, to identification and traceability and to quality records.
In all these fields, welding is hardly distinguished from other industrial operations for which it is advisable to have sufficient documentation for the characteristics of equipment and materials, the provisions taken in the event of non-conformance, as well as all information relative to the traceability of the operations.
Three points, however, deserve a much closer examination. They concern the welding itself and related activities, the personnel in charge of welding, and finally inspection and testing and the inspection and tests themselves. Indeed, in these three fields the particular technical requirements concerned with the application of the general quality principles are supplemented by references to a whole body of specific standards representing a more or less complex architecture, which it seems advisable to expand on in detail.
14.2.3.1. Welding and related activities
Welding and the activities linked with welding must, like all the other activities, have under the heading of quality organization, a program of production comprising a list of and identification of the operations to be undertaken, of the inspection and tests to be carried out as well as references to the applicable processes. This last point is of particular importance and is the object of a series of standards dealing with the specifications and qualifications of welding procedures which we shall come back to.
14.2.3.2. Personnel in charge of welding and inspection
The expression “personnel in charge of welding” traditionally applies to welders involved in manual welding and operators in automatic or semi-automatic processes. For each of these categories it is specified that they must be qualified by a suitable test defined in the series of the standards EN 287 concerning welders or of EN 1418 concerning operators. There is nothing new here except that only one qualification level is used compared to the three levels that appear in the former French standard NF A 88-110. One of the arguments put forward to justify this position was that the qualifying tests generally take place under optimal conditions, making it possible to obtain the best quality levels; furthermore, for the other levels, the need for a qualification remains an issue.
In addition to personnel categories defined above, clause 7.3 of ISO 3834-part 2 introduces the concept of “welding coordination personnel” defined according to three levels of technical knowledge in the ISO 14731 standard “Coordination in welding — tasks and responsibilities”. This function has been developed in detail in the report referred to above (ISO/TR 3834-6) insofar as it is infinitely variable and can be undertaken by various people: welding engineer, welding technologist, production manager, foreman, etc. Before the transcription of EN 719 into the ISO standard, this concept met with a certain amount of difficulty because of the ambiguity of the standard which could imply that a certification by third party was necessary. This is incorrect and we refer readers to the above-mentioned report which contains all the explanations necessary.
It is altogether a different matter for personnel in charge of carrying out non-destructive testing for whom a certification complying with EN 473 “Qualification and certification of NDT personnel — general principles” is necessary. Let us recall that this certification comprises three levels and that it is awarded according to the examination technique employed: ultrasonic, radiographic, magnetic particles, or penetrant testing. The French certification organization is COFREND, the French confederation for non-destructive testing; bilateral agreements of mutual recognition already exist for such bodies and a European organization has been set up.
14.2.3.3. Inspection, examinations and tests
The requirements for quality relating to inspection, examinations and tests depend mostly on good operational welding practice. Before welding it is advisable to identify the products used, parent materials and welding consumables, to check the validity of the qualifications, joint preparations, etc. During welding, it is the welding parameters, the temperatures, etc., which are of most concern; after welding, dimensional checks and non-destructive testing should be carried out.
The series of standards concerning the latter is particularly important, while their structure has been the object of thorough reflection and deserves particular explanation.
14.3. Standards for welding procedure qualification
The standards for welding procedures qualification are among the oldest published by CEN/TC 121, particularly concerning manual arc welding of steels and aluminum alloys. Four parts inaugurated the series of the standards EN 288 “Specification and qualification of welding procedures for metallic materials”:
– Part 1: General rules for fusion welding.
– Part 2: Welding procedure specification for arc welding.
– Part 3: Welding procedure tests for arc welding of steels.
– Part 4: Welding procedure tests for arc welding of aluminum and its alloys.
Their publication was not revolutionary compared to the practices of the time; thus Part 3 did not differ greatly from the French standard NF A 89-010 except in some particular points, for example, the definition of the validity fields or the methods for indentation rows. The general rule remained a choice between “no qualification” or “qualification by test”.
Over the course of time and as the standardization works advanced, complementary parts describing new methods of qualification appeared: use of consumable products subjected to tests, reference to experience, reference to a standard welding procedure, execution of a particular welded joint prior to production, etc.; the general philosophy, based on an honourable intention, is of offering a range of possibilities enabling the choice of the most economical and technically suitable solution.
To this aspect of the problem, which can be considered surmountable, was added the question of extending standards to other welding processes (gas welding, electron beam welding, laser welding, resistance welding, etc.), as well as with other metals (steel or aluminum castings, nickel, titanium, zirconium, copper, etc.). The application of each one of these variables to the various possibilities offered by arc welding on steel or aluminum led, not only to EN 288 comprising some 50 parts, but also completely independent standards, which are diverse in number. Needless to say that the user would have been completely lost.
The search for a practical solution, combined with the fact that a revision made it possible to envisage the publication of these standards internationally, led to a complete recasting of the system, with a general structure, defined in Table 14.1. The main aim was to reduce the number of documents as far as possible by extending the common parts. To complement this, a technical report was drawn up establishing a metallic material grouping system usable for all welding operations; the practical aim has been to obtain validity fields common to all the qualifications, thereby avoiding the existing discrepancies, for example, between welders and welding procedures.
The analysis of the table above emphasizes the following data:
– general rules apply to all processes,
– only stud welding and friction welding do not conform to the general outline, and this takes their specificity into account,
– metallic material grouping systems are common to all the other processes (arc welding, gas welding, electron beam welding, laser welding, resistance welding),
– qualification methods for use of tested welding consumable; by reference to previous welding experience, by adoption of a standard welding procedure, by execution of a particular welded joint prior to production are also common to these same processes. This means that the same type of procedure can be applied,
– concerning the welding procedure test, regroupings were made comprising arc welding and gas welding on the one hand, and EB and laser welding on the other hand. This means that the same types of tests are used and interpreted according to the same methods,
– however, and this is quite normal, the requirements relating to the welding procedure specifications (WPS) are specific to each process.
Despite all these efforts at simplification, the end result still appears to be inaccessible and rather cumbersome to use. This need not be the case in practice, provided precise details are made available as to the potential application fields of the various qualification methods for welding procedures, as well as their limits.
Questions remain, in particular regarding qualifications for procedures based on tested welding consumables. These can be answered by making it clear that the methods of approval of welding consumables are now covered by the European standard EN 13479 “Welding consumables — general product standard for filler metals and fluxes for fusion welding of metallic materials” drawn up in accordance with the European “Construction Product Directive”. In addition, these methods can be agreed between the customer and the supplier.
– WPS: Welding procedure specification
– WP: Welding procedure
– pWPS: Preliminary welding procedure specification
– WPQR: Welding procedure qualification record
It will undoubtedly take some time for each party — client and supplier — to fully take in the possibilities offered by the range of solutions suggested, the advantages afforded by this opening (which takes account of industrial practice), and then choose the most suitable solution from a full knowledge of the facts.
The standard EN ISO 15607 relating to the general rules contains appendices making the precise details necessary available. Equally it describes the course of the procedure, in particular using a diagram such as that in Figure 14.2, thus making it possible to pose the appropriate questions at the appropriate time.
14.4. Non-destructive testing standards
For non-destructive testing, which is the last aspect of quality assurance organization, even if it does not suffice to guarantee a determined level of quality, although this is nevertheless a determining factor for the acceptance of a welded structure or apparatus. Over the last few years it has also been the object of a significant amount of standardization work, the general concept of which has evolved considerably.
The standards relating to the quality requirements for fusion welding (EN ISO 3834 series) only make reference to the applicable EN or ISO standards. It is thus convenient to develop here the principles which governed their development.
Let us point out the current practice first of all. For steel construction, for example, French standard NF P 22-471 “Metal construction — execution of welded joints” describes and defines three classes of defects liable to be encountered in welds. In addition, it specifies the limits of non-destructive testing: up to 40 mm in depth for radiography, starting from 20 mm for ultrasonic. Finally, it presents for each method, in terms of indication levels, the permissible defects according to the degree of quality required.
This presentation offers an undeniable advantage, namely that it gathers in only one document all the information necessary for the user. It does have, on the other hand, some disadvantages:
– the classes of defects are likely to be defined in a different way according to the applications (steel construction, pressure vessels, etc.) whereas the manufacturing technique is similar,
– the operational limits of the various methods are fixed (unless there is a revision of the standard) whereas in reality progress is made or various factors tend to favor a particular method,
– the methods for interpreting the indications evolve, often becoming more complex.
Such a practice could be allowed at a national level, where several texts comprising identical or similar specifications (CODAP for pressure vessels, metal construction standards, etc.) have coexisted for many years. This is less helpful at the European level insofar as the objective is freedom of movement for goods and people by removal of the technico-economic barriers to exchanges.
This takes place by a harmonization of technical specifications and, concerning welding, a “horizontal” approach independent of the applications, which occurs as follows:
– development of a single reference frame for the description and the definition of the defect classes,
– definition of the enforcement modes for each method as well as their validity limits, while also specifying at what moment an indication can be regarded as significant or not,
– interpretation, for each method, of the indication levels it provides by it with reference to the basic defect class.
Such a structure constitutes a tool at the disposal of users, particularly of technical committee members, in charge of the drafting of the European execution standards (CEN/TC 54 for pressure vessels, CEN/TC 135 for steel structures).
Overseeing all of this standardization work is the standard EN ISO 5817 “Welding — fusion welded joints in steel, nickel, titanium and their alloys — quality levels for imperfections”, which describes and defines in order of decreasing severity three classes of defects: B, C and D. It constitutes a reference frame to which specialists in non-destructive testing and end users can refer, the quality level adapted to each case being defined in the application standard or by the designer responsible in liaison with the manufacturer, the user and/or other parties concerned. An equivalent standard exists for aluminum alloy assemblies, EN ISO 10042.
Thus we find then the standard EN 12062 “Non-destructive examination of welds — general rules for metallic materials”. The analysis appearing on the first page states that this standard “gives guidance for the choice of non-destructive testing methods for the examination of welds and evaluation of the results for quality control. It also specifies general rules and standards to be applied to the different types of examination, for either the methodology or the acceptance levels for metallic materials”. It can be considered regrettable that the term “acceptance levels” is employed as it implies a certain ambiguity by mixing two concepts: that of classification and that of qualitative appreciation, the second point being debatable insofar as the criteria of acceptance could not be uniform for all the applications and must remain the responsibility of the users; it can only be a question in fact of “transference”, in terms of indications and according to the method used, of the classes defined in ISO 5817: this could be called the transfer function method. The details are then given, both with regard to the technique and its validity limits as well as the “acceptance levels”, in the standards specific to each method.
Six different examination methods are thus covered: visual, penetrant, magnetic particle, eddy current, radiographic and ultrasonic. The structure of the system can be schematized as in Figure 14.3.
As for the standards dealing with the welding procedure qualification, the unit may appear complex, but it answers a certain logic which corresponds to the reality on the ground.
A designer or manufacturer responsible for a project or a construction must know the nature and the size of permissible defects during its construction and, in general, cannot prejudge the methods of non-destructive testing which will be used. In the system suggested, his only concern will be to choose the defect class tolerated with reference to the basic reference frame, EN ISO 5817 or ISO 10042.
In addition, the independence of the standards with respect to defect classes and the nature of structures or equipment to be produced allows them to develop according to progress in the techniques, without impacting on the basic reference frame or the procedural standards. We thus have a coherent and progressive system.
However, this field still demands a certain adaptation period. Certainly, the scattering of clauses in different documents and the loss of a conclusive overall picture, such as is experienced today in the codes or specific standards, is a matter of regret. The task of the European technical committees in charge of procedural standards is now to take this whole group of concepts into account and as far as possible guide the user in their application.
14.5. Conclusion
The presentation and analysis of documents such as standards, particularly those which cover complex subjects both from a technical and organizational perspective, is never an easy matter. The situation is complicated by the fact that it is evolving. Many standards worked out at the European level have been taken up again at an international level, with technical modifications as well as changes in presentation. Others will follow suit in the near future and this requires vigilance at every moment.
What should be remembered is that welding is a horizontal technique with a plethora of applications, that the processes and methods are in continuous development and are also becoming more complex, and finally that international competition can only proceed normally if it has reference texts, constituted with the consensus of the majority and used as a basis for contracts.
In this context, industrialists involved in welded construction, in co-operation with clients and partners concerned are equipped, by the means of the standardization committees, with the tools allowing them to achieve outcomes that are satisfactory, both in terms of economics and quality levels. For some this represents a change of practice, even of culture, but in the long term everyone will benefit from this.
1 Chapter written by Jean-Paul GOURMELON.