Stochastic ultrasonic scattering from the tips of rough cracks

Lead Research Organisation: Imperial College London
Department Name: Mechanical Engineering

Abstract

The inspection of safety-critical components in the nuclear power industry depends on procedures that can detect defects to a given threshold of severity; the acceptance process for this is known as inspection qualification. Inspection qualification in the UK is a highly developed formal activity, and is representative of the best practice in the world. However it can be very conservative if there is uncertainty in the expected measured response. A vital example is the scattering of ultrasound from the tips of rough cracks, such as thermal fatigue cracks or stress corrosion cracks. Ultrasound scattering from crack tips is widely exploited to measure crack sizes, but while the nature of the scattering is well understood for smooth cracks, scattering from the tips of rough cracks can differ significantly, and is not readily predictable. Consequently the qualification of ultrasound inspections for rough cracks has to be subject to severely conservative assumptions, and even so there remains a risk of misinterpreting findings.

This project aims to bring understanding to the nature of the scattering, and to develop predictive modelling tools, such that these conservative assumptions can be safely eroded and the reliability of inspections improved. This will enable industry to reduce the costs of manufacturing and repairing, and down-time from outages, as well as improving confidence in the safe operation of safety-critical plant. The project will build on a strong UK heritage of the knowledge of ultrasound scattering, including recent work by the proposers on the stochastic nature of wave reflections from rough surfaces. The key aim is to deliver a new analytical approach that will predict the statistically expected scattering from the tips of cracks of given characteristics of roughness. The work will also include experimental investigation of real cracks and numerical modelling studies. The new ideas will be applied to the primary ultrasound inspection techniques of Time-of-Flight-Diffraction, Pulse-Echo, and array imaging. The work will be undertaken as a collaboration between researchers in Mechanical Engineering and in Mathematics at Imperial College.

The proposal is being submitted within the UK Research Centre in NDE (RCNDE) to its targeted research programme. The proposal has been reviewed internally by the RCNDE, approved by the RCNDE board, and supported financially by five RCNDE industrial members.

Planned Impact

Scattered signals from the tips of cracks are vital for the detection and sizing of cracks in safety critical components, and in particular in thick section pressure-containing components in nuclear power plant. The established techniques are Time of Flight Diffraction and Pulse-Echo, both of which rely on the signal from the tip of the crack to indicate its location. Emerging new techniques using ultrasound array imaging also aim to identify the location of the crack tip. The location of the tip indicates the crack length which is the most important information about a crack for the structural integrity evaluation.

Inspection qualification in the nuclear industry is a rigorous process that must be followed in order for a proposed inspection to be permitted. This uses evidence from a range of sources, largely experimental. In the absence of sufficient evidence, conservative assumptions must be made, and these can be very restrictive.

Until recently it has not been possible to manage the uncertainty of randomly varying signals such as are encountered from rough defects except by using very conservative safety factors. However recent progress in handling the stochastic nature of ultrasound scattering and in being able to perform simulations of large numbers of realisations has made it possible to address this. Success with this project in understanding and predicting the stochastic scattering from crack tips will enable a step change in the inspection of components that might contain rough cracks. This will reduce conservatism in the assessment, thus enabling huge reductions of costs. It will also improve confidence in the inspections.

The project is strongly supported by five industrial members of the RCNDE who are leading companies in the inspection and management of nuclear plant, and who share the same interest in pursuing this goal. They have identified this challenge to be one of the most important topics for research. It is also identified as a research priority by the UK's Office for Nuclear Regulation (ONR). This is vital work both for the existing fleet of power stations and as we move forward to the design and inspection planning for next generation power stations. The successful delivery of new capability will be of immediate use for exploitation by these companies.

Publications

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Haslinger S (2021) Prediction of reflection amplitudes for ultrasonic inspection of rough planar defects in Insight - Non-Destructive Testing and Condition Monitoring

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Haslinger S (2020) Elastic shear wave scattering by randomly rough surfaces in Journal of the Mechanics and Physics of Solids

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Haslinger S (2021) Time of flight diffraction for rough planar defects in NDT & E International

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Sarris G (2021) Attenuation of Rayleigh waves due to surface roughness. in The Journal of the Acoustical Society of America

 
Description Important progress was been made in the understanding of the reflection and scattering of ultrasound waves from a crack whose surface is rough. This included the reflection and scattering from the surface and also the reflection and scattering from the crack tip. This understanding and the developed theory enabled the development of a predictive capability to anticipate the statistically expected amplitude of reflection/scattering when only the geometric statistics of the rough surface are known. This is is a very useful outcome for industry, where it is critical to know the expected amplitudes of reflection and scattering in order to demonstrate the sensitvity of candidate inspection configurations.
Exploitation Route The project included strong engagement with 5 industrial partners who have taken this capability into industrial use.
Sectors Aerospace

Defence and Marine

Energy

Manufacturing

including Industrial Biotechology

URL http://www.scatter.software
 
Description Know-how for Non Destructive Evaluation (NDE) of cracks in power station components has been transferred to the NDE departments of the collaborating industrial partners. An engineering doctorate student was recruited for a technology transfer project at one of these partners. A software package embodying new capabilities that were delivered by the project was developed and issued to the 5 industrial partners. This has been used by them for industrial applications.
First Year Of Impact 2020
Sector Aerospace, Defence and Marine,Energy
Impact Types Economic

 
Title SCATTER - software tool to predict ultrasound scattering from defects 
Description Software package was developed to embody the scientific output of the project. The tool predicts the scattering of ultrasound from rough defects. It was created spoecifically for the industrial partners, to embody the capabilities that had been published openly, but in a convenient form for them to use in industry for the planning of safety-critical ultrasound inspections. 
Type Of Material Improvements to research infrastructure 
Year Produced 2021 
Provided To Others? No  
Impact We have been informed that it has been put to use amongst the five industrial partners, but there are no public reports of this yet. 
URL http://www.scatter.software/
 
Description Amec FW ultrasound NDE 
Organisation AMEC
Country United Kingdom 
Sector Private 
PI Contribution Ultrasound capabilities for NDE
Collaborator Contribution Cash, samples, steering
Impact publicactions, technology transfer
Start Year 2011
 
Description BAE Systems 
Organisation BAE Systems
Department BAE Systems Submarine Solutions
Country United Kingdom 
Sector Private 
PI Contribution Research into the nature of ultrasound scattering from defects with rough surfaces, including the tips of cracks. This is vital for the improvement of the inspection of safety-critical plant components, especially to identify the lenghts of small cracks. A software package at the end of the project that delivers the outcome: a model that predicts the sound scattering from defects.
Collaborator Contribution Industrial context on the inspection need and the methodology for inspection and qualification, cash.
Impact Multiple publications disseminating the new predictive capability. A software package for the industrial partners to use this new predictive tool
Start Year 2016
 
Description EDF ultrasound NDE 
Organisation EDF Energy
Country United Kingdom 
Sector Private 
PI Contribution Ultrasound NDE methods for power plant components
Collaborator Contribution cash, steering meetings
Impact technology transfer, publications
Start Year 2011
 
Description National Nuclear Laboratory 
Organisation National Nuclear Laboratory
Country United Kingdom 
Sector Public 
PI Contribution Research into the nature of ultrasound scattering from defects with rough surfaces, including the tips of cracks. This is vital for the improvement of the inspection of safety-critical plant components, especially to identify the lengths of small cracks. A software package at the end of the project that delivers the outcome: a model that predicts the sound scattering from defects.
Collaborator Contribution Industrial context on the inspection need and the methodology for inspection and qualification, cash.
Impact Multiple publications disseminating the new predictive capability. A software package for the industrial partners to use this new predictive tool.
Start Year 2016
 
Description R-R ultrasound NDE 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution Develop ultrasound NDE methods for use by R-R for inspections of nuclear power plant components
Collaborator Contribution Cash, steering meetings, deployment of outcomes within the company
Impact Technology transfer to partners, publications
Start Year 2010