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Achievement & Reliability of Non-Destrucitve TestingJ M Farley, BSc, PhD, CPhys, FInstNDT
Director of Technology, Mitsui Babcock Energy Limited, Renfrew, UK
Member of Board of Directors, European Federation for NDT
General Secretary, International Committee for NDT.
A key objective of national NDT Societies, regional groupings of NDT Societies and the ICNDT is the achievement of reliable inspection particularly for safety-critical plant. The paper critically reviews the infra-structure which has grown up to assist in the achievement of reliability, identifying gaps and pointing out where users can either directly, or through their national societies, assist in achieving improvements.
Keywords: Quality, reliability, best-practice, accreditation, certification
Non-Destructive testing (NDT) has a number of important roles to play in ensuring the through-life quality and reliability of many important products whose integrity is of paramount importance. The traditional role of NDT in quality control during manufacture - predominantly defect detection - has been complemented in recent years with materials characterisation, stress measurement and inspections in-service. The correct application of NDT can prevent accidents, save lives, protect the environment and avoid economic loss.
To achieve these objectives there is a need to manage NDT operations to ensure that they can be relied upon by the designers and engineers who call for their use. Many of the necessary controls are available through the "NDT infrastructure" which has been established in many countries - comprising research and development, national standards, training courses, personnel certification, third party inspections etc. These infrastructures are quite sophisticated and most complete in the manufacturing quality control sphere of NDT, particularly in those geographical areas where ISO 9001 certification of quality assurance demands comprehensive systems be in place. They are nowhere near so complete in the newer applications of NDT or in-service inspection and need to be developed.
As world trade rapidly becomes more liberalised, the NDT infrastructures which were originally national in their coverage, need to become international. For example, national standards for NDT in individual European countries are being superseded by European (CEN) standards. Of particular interest are the European Standard for Qualification and Certification of Personnel in NDT (EN473) and an International Standard on the same subject (ISO 9712). There also exists a series of European Standards (EN45000 series) which govern accreditation of NDT Laboratories, Inspection Bodies and Personnel Certification schemes. These Standards are used to varying degrees in the countries of the European Union, EFTA and the countries of Central and Eastern Europe (including the former Soviet Union).
Quality in execution of NDT operations demands attention to a series of interlinked aspects extending from research and development, codes and standards, equipment, personnel training and certification to the effects of human reliability and the influence of auditing and surveillance. These aspects can be represented as links in a chain as shown in Figure 1.
|Fig 1: NDT Quality Chain.|
The chain will only be as strong as its weakest link. Extra attention to one link in the chain cannot compensate for lack of attention to another - just as a strong link in a chain cannot compensate for a weak link. For example, personnel certification as a measure of the capability of personnel to carry out NDT is a vital link in the chain. Standards, procedures, equipment controls, audits, surveillance etc. cannot achieve quality if the practitioner carrying out the NDT is not adequately capable. The converse is also true. An NDT skills certificate will not guarantee quality if the practitioner is expected to use inadequate equipment, is demotivated or demoralised by being put under inordinate pressure of time or by being asked to work in impossibly difficult conditions. Neither will a personal certificate ensure quality if the practitioner is asked to carry out tasks which are outside the scope of his certificate without being given the guidance of job-specific training.
National and international standards for quality systems such as ISO 9001 require management to establish quality systems to control all activities which affect quality including NDT. The quality system must address each of the links in the NDT quality chain - to ensure that all the links are in place and properly joined.
An NDT infrastructure has gradually grown up which provides some of the foundation stones and frameworks with which NDT quality systems can be constructed.
In Figure 2 the heavy boxes represent the "doing activities" that make up NDT operation, i.e. Procedures, Equipment, Training and Certification, Human Factors, whilst the lighter boxes represent the various measures designed to achieve quality. Standards, Validation, Authorised Inspection Bodies, Certification Bodies and Accreditation Bodies can all contribute.
|Fig 2: The NDT Quality infrastructure.|
Codes and Standards Codes and Standards have a vital role to play in achieving quality. There are International, National and now European Standards for NDT techniques, equipment and personnel certification. American standards (ASME, ASTM etc.) are widely used.
In fact most Codes and Standards focus on manufacturing inspections and in some cases in-service inspections may be outside the intended scope.
Personnel Training and Certification
The training of NDT personnel is very important - both before and subsequent to certification examinations. Attention must be given to job-specific training before an operator is asked to carry out jobs which may be outside the scope of his certificate.
In the field of personnel certification there are two types of standards: those which cover central, independent certification and those for in-house certification. Central independent certification as defined in standards such as the International Standard ISO9712  and its European equivalent EN473  is increasingly being accepted internationally, including in the United States. The American ASNT document SNT-TC-1A is widely used in place of a standard for in-house certification.
There is a gradual coming together of the central independent and in-company approaches. The former are increasingly aware of the need for the central certification to be used in the correct way - as part of an organisation's quality systems for NDT - and the standards for in-house certification are bringing in requirements for external assessment eg. independently certified Level 3s.
In most countries in Europe there is a 'national' Certification Body which provides NDT personnel certification to the EN473 standard in each main NDT method at three levels (Level 1, 2 and 3).
Due to the lack of detail in the Standard there is some considerable variation between different Schemes, in depth and breadth of certification and thus in the need for in-house job-specific training and assessment.
Audits and Surveillance
Audits and surveillance are the traditional role of the "Inspection Body". Audits/surveillance aim to ensure that a procedure is properly applied but cannot, without validation, demonstrate the capability of the procedure.
Increasingly Inspection Bodies in Europe are gaining accreditation to EN45004. This service is provided in the UK by UKAS - the United Kingdom Accreditation Service.
Certification/Accreditation of NDT Operations
Certification Bodies have a role to play in certifying quality systems to ISO9001. Many manufacturing companies which carry out NDT will have their NDT operations covered by the assessment by a certifying body, but NDT will be unlikely to receive very detailed attention.
In a growing number of countries in Europe (including FSU countries such as Russia and Belorussia) NDT Service company operations are being accredited by Accreditation Bodies such as UKAS to the European Standard EN45001 supplemented by various Guidelines documents. For critical inspections of nuclear power plant in Sweden such accreditation by SWEDAC is mandatory. EN45001 assessments are much more comprehensive and searching than a 'quality systems' audit to ISO9001 with greater emphasis on the inherent technical capability of the organisation.
Qualification of NDT procedures, equipment and personnel
The process of Qualification, also known as Validation or Performance Demonstration has been developed as a result of the need to assure the quality of inspections of nuclear power plant.
In the USA, following analysis of the results of the PISC II Trials, the ASME XI committee adopted the principles of validation or performance demonstration and introduced Appendix 8 to Section XI of the ASME code to define how performance demonstration trials should be conducted. Performance demonstrations to these code requirements are now being implemented through the Performance Demonstration Initiative (PDI) managed by the Electrical Power Research Institute (EPRI).
In the countries of the European Union and Switzerland, a network of the nuclear electricity utilities and inspection companies known as ENIQ, (the "European Network for Inspection Qualification") have co-operated to draw up a document which deals with the objectives and role of NDT qualification, including principles for the derivation of basic qualification requirements and how to organise the process of NDT qualification. Utilities and regulators in Europe have begun to utilise the ENIQ guidelines. Under the auspices of EPERC studies are being conducted into how Inspection Qualification might be applied more widely and the CEN Technical Committee TC138 has established a working group to draft a general standard for qualification of inspections.
Responsibility for the various elements of the infrastructure rests with a variety of bodies, none of which are wholly devoted to NDT. These include Standards Bodies, Certification Bodies and Inspection Bodies, each of which concentrates on its own elements of the infrastructure. None is concerned with the complete quality chain.
Individual users and suppliers of NDT services are able to influence the development of the NDT quality infrastructure through participation in advisory committees, management committees and standards organisations. National NDT societies are in a position to take an overview of NDT quality and the more active seek to influence the whole quality chain.
To increase their influence at the European level where, increasingly, decisions are taken, the national NDT Societies have combined to form the European Federation for NDT (EFNDT). EFNDT is a non-profit legal entity registered in Brussels. National NDT Societies within the UN definition of Europe are eligible for membership. Each is represented on the General Assembly which elects a President and Board of Directors. A Secretariat is provided by one of the member national societies, currently the French NDT Society (COFREND). EFNDT has established a series of working groups covering topics such as WG1 Qualification and Certification, WG3 European Certification Process, WG4 Accreditation of NDT laboratories and Inspection Bodies. These groups seek to support and complement (rather than compete with) the European committees/working groups of EA (European Accreditation), CEN, etc. and support national societies in their work at local level.
WG1 has developed a mutual recognition agreement (MRA) between their respective Certification Schemes. Twenty-five national NDT Societies have signed the MRA and sixteen Certification Schemes have gained EFNDT Recognition.
Further steps are underway to harmonise certification throughout Europe through the establishment of ECP - European Certification process, a joint development by the British, French and German NDT Certification Schemes on behalf of EFNDT.
At International level, the ICNDT has revised its constitution with a view to improving its influence and effectiveness. The International Committee for NDT was formed in 1960. For most of its existence ICNDT's main role was to organise the World Conference. Since the mid 90s the more active members of ICNDT have been seeking to strengthen the organisation and make it more active. This culminated in the adoption of a New Constitution at the ICNDT meeting in Rome - by the 50 member National NDT Societies. The 50 National Societies each nominate 2 representatives to the ICNDT Committee. The committee then elects a Chairman, General Secretary and a Treasurer each for four years. It also elects Honorary Members.
These people along with nominees by each of the Regional groups like EFNDT and the Asia Pacific Region form the Policy and General Purposes Committee. A Secretarial service is provided by an NDT Society. Separately (now), the ICNDT chooses the Society to hold the next World Conference and that Society nominates the World Conference President.
5.1 Management of NDT
It is clear from the results of exercises such PISC II, III, PANI etc. that there is often an over-reliance on use of standards and personnel certification as a guarantee of quality in NDT with both purchasers and suppliers of NDT services failing to recognise when they are moving outside the normal scope of standard inspections, training and certification. More emphasis should be placed on the use of all relevant elements of the NDT quality infrastructure ie.
It would be appropriate to recommend that the responsible engineer should check the qualification/certification of the Operators proposed against the requirements of the job, bearing in mind that "not all ISO 9712/EN473 qualifications are equal".
5.2 Contractual arrangements
Contractual arrangements should be clear in the definition of who takes responsibilities. Users should think in terms of employing a service company capable of accepting technical responsibilities and providing back-up rather than employing operators as individuals. Either the purchaser of the service retains the key responsibility and simply 'hires a pair of hands' or the purchaser buys a service and specifies clearly his requirements. The supplier of the service may then have to qualify his offer if the demands are more onerous than he can guarantee.
The time allowed for preparation and then for execution of an inspection is crucial. Sufficient time must be allowed for both and the contractual arrangements must allow the inspection company to recover its costs.
5.3 Human Factors
The NDT infrastructure should be further developed by addressing the subject of human factors which influence reliability. Attention is required to human motivation to achieve quality. In fact the motivation and commitment to quality of NDT personnel is of prime importance in the quest for total quality in NDT operations. It is most unlikely that quality can be achieved by quality system certification, standards and validation unless the individuals executing NDT are properly motivated.
In some organisations the NDT staff are salaried, work regular hours and are included with other staff in personnel training schemes, staff development schemes, quality circles etc., i.e. they are fully integrated, have the means of achieving a satisfying and worthwhile career and can call upon technical and managerial support. In contrast, in other cases NDT is carried out by agency staff or by temporary personnel, often self-employed. In many cases payment is by the hour or even by the metre of weld tested. Extended shifts and long periods without a day off are common. There are no paid holidays, no sick-leave and no technical or safety support by the employer. This situation has probably arisen because of the portability of personal NDT certificates on the one hand and commercial pressures on the other. It is not conducive to high quality.
There is a need for a code-of-practice on employment conditions for NDT staff. It is necessary to set down guidelines based on research as to what are appropriate employment conditions and working arrangements for personnel engaged on quality critical activities.
In the UK, the Health and Safety Executive, through a joint HSE-Industry Working Group has developed a document "Best Practice for the Procurement and Conduct of NDT". Part 1 Manual Ultrasonic Inspection  is available to the public via the HSE web-site. Other parts relevant to other NDT techniques will be published progressively.
The author is grateful to his company Mitsui Babcock for support and to his colleagues there and in EFNDT and ICNDT for useful discussions. The views/opinions expressed are personal.
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