Knowledge gaps in fitness-for-service assessment procedures; summary of the 2nd ‘Mind the Gap’ workshop

Isabel Hadley*, Uwe Zerbst, Harry Coules, Peter James, John Sharples, Shivaprasad Shridhara Bhat, Nicolas O Larrosa

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

1 Citation (Scopus)

Abstract

In 2015, the University of Manchester hosted a workshop (‘Mind the Gap’) aimed at identifying gaps in a number of structural integrity fitness-for-service procedures, including R5, R6, BS 7910 and API/ASME. The findings were subsequently summarised in a journal paper and shared with the relevant stakeholders. A second workshop, this time hosted by the University of Bristol in 2017, was intended to build on the findings of the earlier event, identifying which gaps had been filled, which remain and whether new ones have been identified in the meantime. ‘Mind the Gap 2’ was wide-ranging, including consideration of failure by fracture, fatigue crack growth, high temperature creep and environmentally assisted crack growth, along with the use of innovative techniques to follow the progress of crack growth from the atomic to the macroscopic scale. A summary of the whole event is thus outside the scope of a single paper, so here we concentrate mainly on advances in the fields of fracture and fatigue, on the interface between inspection and ECA, and on how developments are being incorporated into structural integrity procedures. There is a particular emphasis on the energy transition in the UK, where the planned energy mix will include both nuclear power and offshore wind.
Original languageEnglish
Article number104883
JournalInternational Journal of Pressure Vessels and Piping
Volume202
Early online date5 Jan 2023
DOIs
Publication statusE-pub ahead of print - 5 Jan 2023

Bibliographical note

Funding Information:
Dr Coules acknowledges technical contributions from Dr Bostjan Bezensek and funding from the UK Engineering and Physical Sciences Research council under grant no. EP/M019446/1 .

Funding Information:
Dr N.O. Larrosa would like to acknowledge discussions with Dr J. Zhang on the NDT modelling of non-sharp defects, and Dr Anthony Horn and Prof Bob Ainsworth on the fracture behaviour of non-sharp defects and the funding provided by the UK Engineering and Physical Sciences Research Council under grant no. EP/S012362/1 .

Funding Information:
The work reported within section 3 was funded by the UK Department for Business, Energy and Industry Strategy ( BEIS ). The paper is published by permission of Jacobs and NNL.

Funding Information:
In the UK, NDT research and development is spearheaded by the UK Research Centre in NDE (RCNDE) with active industry-academic collaboration [ 8 ]. The centre is co-funded by Engineering and Physical Research Council ( EPSRC ) and its industrial members. Through this collaboration, the centre aims to support world-class scientific NDT research and deliver industrial benefits. Conversely, activities within the SI communities are promoted by bodies such as the UK Forum for Engineering Structural Integrity (FESI). They foster the exchange and enhancement of knowledge of engineering structural integrity by drawing together the experience and expertise of relevant academic, regulatory, industrial, and professional organisations and individuals to assist in the assurance of the integrity of engineering structures and components [ 9 ]. Historically, SI and NDT engineers/scientists and their respective professional bodies have largely worked independently. A significant number of grants and fellowships have separately addressed various aspects of NDT and SI assessments but do not on linking these two sectors. RCNDE laid out their vision on the role of NDT and monitoring towards enabling the fourth industrial revolution [ 10 ]. The report states that a closer understanding of the fields of NDT and SI offers opportunities to enable better engineering integrity judgements and decisions. To achieve this, both RCNDE and FESI jointly organized a workshop titled “Non-destructive Evaluation and SI” in late 2017 to explore opportunities for research and engineering practice through closer collaboration. This has led to a grant being awarded by the Engineering and Physical Sciences Research Council ( EPSRC ) to the University of Bristol which aims to explore the possibility of linking SI and NDT communities. This multidisciplinary project cuts across multiple academic fields, i.e. NDT, mathematical modelling, engineering structural integrity, finite element analysis, and engineering design – aiming to produce a step change improvement in damage tolerance methods for the next generation of design and structural integrity procedures, allowing enhanced efficiency of assets [ 11 ].

Funding Information:
In the UK, NDT research and development is spearheaded by the UK Research Centre in NDE (RCNDE) with active industry-academic collaboration [8]. The centre is co-funded by Engineering and Physical Research Council (EPSRC) and its industrial members. Through this collaboration, the centre aims to support world-class scientific NDT research and deliver industrial benefits. Conversely, activities within the SI communities are promoted by bodies such as the UK Forum for Engineering Structural Integrity (FESI). They foster the exchange and enhancement of knowledge of engineering structural integrity by drawing together the experience and expertise of relevant academic, regulatory, industrial, and professional organisations and individuals to assist in the assurance of the integrity of engineering structures and components [9]. Historically, SI and NDT engineers/scientists and their respective professional bodies have largely worked independently. A significant number of grants and fellowships have separately addressed various aspects of NDT and SI assessments but do not on linking these two sectors. RCNDE laid out their vision on the role of NDT and monitoring towards enabling the fourth industrial revolution [10]. The report states that a closer understanding of the fields of NDT and SI offers opportunities to enable better engineering integrity judgements and decisions. To achieve this, both RCNDE and FESI jointly organized a workshop titled “Non-destructive Evaluation and SI” in late 2017 to explore opportunities for research and engineering practice through closer collaboration. This has led to a grant being awarded by the Engineering and Physical Sciences Research Council (EPSRC) to the University of Bristol which aims to explore the possibility of linking SI and NDT communities. This multidisciplinary project cuts across multiple academic fields, i.e. NDT, mathematical modelling, engineering structural integrity, finite element analysis, and engineering design – aiming to produce a step change improvement in damage tolerance methods for the next generation of design and structural integrity procedures, allowing enhanced efficiency of assets [11].From an NDT viewpoint, researchers have developed solutions to model the scattering of ultrasonic waves for circular holes, and approximate solutions using Kirchhoff approximation for a flat elliptical crack [35], a semi-circular surface crack [36] and an irregular void [37]. However, no analytical models are available for complex defect geometries formed during manufacturing or in-service. Numerical modelling approaches, based on finite element [38–41], finite difference [42,43] or boundary element methods [44], appear promising for modelling non-sharp defects. The EPSRC has funded a project led by the University of Bristol focused on developing NDT and fracture assessment methods for non-sharp defects. This project combines fracture mechanics arguments to explore the areas for which accurate characterisation of non-sharp defects will provide an enhancement of the structural integrity arguments. Based on discussions from the previous workshop [5], this project considers the use of a modified Q stress parameter for the characterisation of constraint in the case of a notch, thus using a single parameter to predict the effect of notches and constraint on apparent fracture toughness. However, the invalidity of the classical Q as a constraint parameter can be seen from Fig. 7, where due to the different shapes of the stress field for cracks and notches, it is possible that the point at r=2J/σy value (typical value used to compare stress fields) may lie inside of the finite strain region for blunt notches, as the blunting zone for a blunt notch tends to be larger in size than for a sharp crack (i.e. this zone encroaches on the K-dominated zone from the inside). The figure also shows that, as the notch tip radius increases, the finite strain region becomes larger and more spread out than crack-tip stress fields. The result is that the global stress fields outside the K-dominated zone tend to invade the K-dominated zone more readily than for crack-tip stress fields.The work reported in sections 1.2 and 1.3 was carried out under the Core Research and Exploratory programmes of TWI, and is published with their agreement. The NDT concept was developed by Colin Bird (CRB Inspection) whilst employed by TWI. Dr N.O. Larrosa would like to acknowledge discussions with Dr J. Zhang on the NDT modelling of non-sharp defects, and Dr Anthony Horn and Prof Bob Ainsworth on the fracture behaviour of non-sharp defects and the funding provided by the UK Engineering and Physical Sciences Research Council under grant no. EP/S012362/1. Dr Coules acknowledges technical contributions from Dr Bostjan Bezensek and funding from the UK Engineering and Physical Sciences Research council under grant no. EP/M019446/1. The work reported within section 3 was funded by the UK Department for Business, Energy and Industry Strategy (BEIS). The paper is published by permission of Jacobs and NNL.

Publisher Copyright:
© 2023 Elsevier Ltd

Keywords

  • Flaw assessment procedures
  • Non-sharp defects
  • Flaw interaction
  • Codes and standards
  • Nuclear reactor systems

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