Tuesday 18 September
Session 1B – NDT Applications
The body is the sensor
Dr M Thompson, Dr M L Harper
Mecon Ltd
An autonomous device called the 'Urchin' is being developed to travel through underground water pipes to listen for leaks. The Urchin consists of a hollow plastic ball just 75 mm in diameter. It must record continuously for best part of a day. It must not get lost and must 'know' where it is sufficiently accurately to locate the leaks after post-processing data. Pressures can be high, up to 16 Bar or more and there must be no water penetration. Therefore one requirement is to maximise the sensitivity to acoustic leak noise without any penetrations through the skin of the Urchin. At the same time any other background noise such as that associated with pipe wall interaction must be minimised. This paper will follow our logical path through the possible ways of achieving these requirements and describes the final solution.
Robotic pipe crawling platform for NDE
Liam Mackenzie, Gareth Pierce, Gordon Hayward
Centre for Ultrasonic Engineering, Department of Electronic and Electrical Engineering, University of Strathclyde, 204 George Street, Glasgow G1 1XW, UK. E: liam.mackenzie@eee.strath.ac.uk
The processing cells within a nuclear plant typically contain several kilometres of tightly packed pipework with the only access to these pipes being via a removable concrete plug in the radiation shield; this plug may be several meters from the inspection location. Due to the hazardous and complicated nature of such cells it is neither safe, nor practical for a human to carry out the inspection by hand. Coupled with the growing trend towards extending the working lifetime of the existing power generation infrastructure using condition monitoring and NDE there is a need for a novel robotic system for external pipe inspection. This paper presents a wireless inspection robot capable of travelling along the outside of a pipe at any orientation and avoiding obstacles such as pipe hangers while carrying a variety of NDE payloads. The robotic platform will provide a 360º inspection of a circumferential weld using attachable transducer modules, the results of which can be processed on-board or transmitted directly back to a base station located at the cell entry point for more detailed analysis. An on-board camera allows real time image processing to identify potential defects.
Effectiveness of screening methods for in-service inspection
Fraser Hardie
Doosan Babcock Energy Ltd
A wide range of advanced NDT methods which allow large area screening of a component for significant degradation (often through corrosion) has evolved over the last ten years or so. These specialised techniques are not always as sensitive as the more conventional NDT methods but they may provide a means of inspecting areas which would otherwise be uninspectable. Examples include long range ultrasonics, pulsed eddy current and saturated low frequency eddy current techniques.
There is a lack of objective information on the capability and limitations of screening methods. Guidance is required on how to select a particular method, what it can detect (as well as what it can miss), and what the level of confidence is in no degradation being present if none is detected.
This paper presents a summary of this Group Sponsored Project which aimed to:
- Provide an objective and unified source of information on the effectiveness of screening methods for a variety of applications.
- Establish guidelines on the use of screening methods.
- Produce guidelines on how to use the data generated as an input for risk based and non-invasive inspection programmes.
- Provide a forum for the discussion and agreement on the application and effectiveness of screening methods between interested parties (regulators, certifying authorities, plant operators and inspection vendors).
John Rudlin, TWI, and Antony Maxwell, NPL.
Surface performance is critical to almost every engineering material and the ability to apply a durable coating (functional and/or decorative) is often a key requirement. The capability to determine reliably regions of poor adhesion between a substrate and a coating or adhesive is often critical in manufacturing QA and/or for maintenance purposes.
Current adhesion measurement techniques tend to be destructive and a non-destructive technique is strongly desired by industry. This paper describes work carried out to examine a number of methods for non-destructive adhesion measurement. Many different coating types were investigated.
The work concluded that the optimum choice of technique is highly dependent on the coating type, and that development of special techniques for some coating types is necessary.
Reliable crack detection in Thermosonics NDT
Marco Morbidini and Peter Cawley
RCNDE (United Kingdom Research Centre for NDE), Imperial College London, Mechanical Engineering Department, South Kensington Campus, London, SW7 2AZ
Thermosonics (also known as Sonic-IR) has potential for detecting small fatigue cracks in metals. A high-power fixed-frequency acoustic horn excites a high-amplitude multiple-frequency cyclic strain in the test-piece which causes heating of the defect by friction. The resulting local increase in temperature can be detected by an IR camera. In this study we prescribe the threshold vibration level that must be achieved at the crack in order to be able to measure a satisfactory temperature rise. Given the non-reproducible and non-stationary nature of the excitation, it was necessary to introduce a unified measure of excitation (which we call Heating Index and is essentially a combination of vibration amplitude and frequency) and to calculate it from the strain recorded during each excitation pulse using the Short Time Fourier Transform method. We calibrated the Heating Index against the measured temperature rise in multiple tests on each of 14 cracked beams with cracks measuring from around 3% to 40% of the total cross section. Then we plotted the thermosonic efficiency of each crack (the ratio of temperature rise to Heating Index) versus crack size to obtain a curve which represents the sensitivity of our implementation of Thermosonics testing. The threshold Heating Index required to reliably detect any crack of predetermined target size can be estimated from this curve and is a function of crack size, camera sensitivity and spatial averaging used to obtain the images.
Recent advances in robotic coiled tubular assessment
R K Stanley
In-service non-destructive inspection of coiled tubular (CT) and other steel piping product has taken on increased importance, especially with coiled tubing strings being produced for high-pressure service. We have taken a twopronged approach, based upon our associated with the Mechatronics Department at Rice University, Houston, Tx.
First, we report on the development of an internal inspection robot of diameter 1.75 in (44 mm) for which we have developed a three-axis magnetic flux leakage (MFL) approach, using permanent magnet magnetisation, and the ability to store large amounts of data (Figure 1). A robot has also been designed for small D-bends in steel (and other) tubing, aimed at the processing industry, and for long runs at high pressure in installed line pipe. Progress with the internal robots has aided us to develop a small inspection system that can be mounted in coiled tubing rigs, and inspect the tubing wall from the outside. The robot will also measure the wall thickness of carbon-steel tubulars magnetically, and the thickness of internal plastic coatings using an eddy current method.
Second, we are performing analyses that are aimed at reconstructing defect shapes from their MFL signals so that relatively accurate measurements of wall condition can be made from either surface. Solutions to this 'inverse problem' should be of much value in performing internal tubing inspections in the petrochemical, paper, nuclear and other industries.
Data are presented from a run through 3000 ft (914.4 m) of coiled tubing. We are also investigating problems with placing ultrasound into small-diameter tubing walls by the use of phased array ultrasound.
Session 2B – NDT in Industry
Development of novel 'Short Range Ultrasonic Guided Wave (SRUGW)' technique for lighting poles inspection
M Ziolkowski, R Taneja, D S Dulay, I Rafiq, D Jani
NDT Consultants Limited, Middlemarch House, Siskin Drive, Coventry CV3 4FJ, UK
Long range ultrasonic technology, which essentially uses a number of piezoelectric transducers arranged spatially to flood the volume of the component with ultrasonic energy is well known. The defect detection capability of guided wave ultrasound is not affected by presence of bends, welds, distributaries etc. However, the amount of ultrasonic energy reflected from a defect is affected by the fluid through piping, covering over piping etc. SWRI USA has developed a new guided wave ultrasonic technology based on principle of magnetostriction. MSS technology requires bonding a strip of magentostrictive material to the part under test and using a simple single transducer for transmission of ultrasonic energy.
In this paper novel application of standard long range applications for short length objects has been proposed. Short range ultrasonic guided wave (SRUGW) technology for inspection of lighting poles has been investigated. The project aims to study the response of artificial defects in the near zone and conceptualize procedure for its deployment in the field. In order to size defects the sensitivity and shadowing curves has been calculated. Finally Short Range Guided Waves with the help of Finite Element Analysis has been modelled and good agreement to experimental work has been obtained.
Monitoring of wind turbine blade structures using acoustic emission
Kenneth Burnham, S Gareth Pierce and G Hayward
Centre for Ultrasonic Engineering (CUE), Department of Electronic & Electrical Engineering, University of Strathclyde, Royal College Building, 204 George Street, Glasgow G1 1XW. T: +44 (0) 141 548 4019; F: +44 (0)141 552 2487; E: kenneth.burnham@eee.strath.ac.uk
Offshore wind turbine installations have a number of advantages compared with onshore developments. Offshore sites, for example, benefit from faster and smoother winds, less turbulence and yield a greater generation of electricity per square metre of swept rotor area. Less turbulence also results in an increased component life-cycle. The UK, alongside seven other sea-bordering EU member states, represents 90% of the offshore wind energy potential within the EU. The challenge is to extend component lifetime, increasing energy yield per turbine.
Rotor blades are a significant structural component in an overall wind turbine system, typically accounting for 30% of lifecycle costs and 34% of turbine downtime. Despite their importance, there is currently very little monitoring of the structural integrity of rotor components, and what does exist is fairly limited. This paper focuses on acoustic emission to assess the integrity of typical rotor blade structures. The limiting aspects of the technique, based on the physics of acoustic wave propagation in typical structural components are discussed, together with an appraisal of the proposed assessment methodology.
Ultrasonic detection of fretting cracking in generator teeth
X Jian*, S Smalley
Phoenix Inspection System Ltd, Warrington, WA1 4RZ, UK. *Email: xjian@phoenixisl.co.uk
J Knowles, R Moser
R&D Inspection Technologies, ALSTOM Power Service, Switzerland
K Quirk
Phoenix Inspection System Ltd, Warrington, WA1 4RZ, UK
This paper presents an ultrasonic inspection of fretting cracking in generator teeth. Access restriction to the fretting surface to be inspected is applied. The angle between the fretting surface and the top surface of a tooth where ultrasonic transducer rests is varied dependent on the manufacturer and the mode of the power generator. A model has been developed which allows quick calculation of the optimum orientation of an ultrasonic transducer of a specific beam angle for a fretting crack of a specific orientation. This model has been verified by experimental measurements. This work is very useful for the design of an array of transducers for automatic 'one-pass' ultrasonic inspection of rotor tooth fretting cracking.
Prediction of plastic anisotropy from ultrasonic testing on nominally pure and AA3104 aluminium sheets
J Morrison1, S M Dixon1, M D G Potter1, S Essex1, C Davis2
1University of Warwick, Department of Physics, Coventry, West Midlands, CV4 7AL
2School of Engineering, Metallurgy and Materials, The University of Birmingham, Birmingham, B15 2TT, UK
T: +44 (0)24 7652 3965; F: +44 (0)24 7669 2016; E:phraak@warwick.ac.uk
Texture information derived by non-destructive means has been used with limited success to determine formability parameters of sheet metals in a number of specific metallic alloys. Ultrasonic measurement of the zero order symmetric (S0) lamb wave velocity as a function of angle to the rolling direction reveals a metal sheets elastic anisotropy. With knowledge of the behaviour of the single crystal elastic properties in the polycrystalline aggregate, the sheets crystalline texture may be determined. Evaluation of orientation distribution coefficients which sufficiently describe a sheets texture is therefore achieved and can be useful for the non-destructive prediction of formability parameters. EMATs (Electromagnetic Acoustic Transducers) perform this ultrasonic measurement without contact which allows relatively efficient generation of the in plane wavepacket as compared to piezoelectric transducers, whilst allowing for operation on a moving sample. Most importantly, because the S0 wavepacket employed for ultrasonic testing measures the bulk elastic anisotropy it, easily, samples a statistically significant number of grains through the entire thickness of the sheet. It therefore avoids spurious results which may be obtained when local texture is assumed to provide an indication of a samples global texture as is likely to be the case when diffraction techniques such as XRD (X-ray diffraction) EBSD (electron backscatter diffraction) are used to determine texture at the samples surface. In order to achieve the level of sampling as that achieved ultrasonically with diffraction the sheet must be destroyed in a relatively time consuming measurement. A comparison of textures obtained by EBSD and ultrasonic methods has been performed and the use of this texture information to provide formability parameters, determined by mechanical testing, has been investigated for a number of nominally pure aluminium sheets and commercial can body stock sheets of AA3104 aluminium.
Ultrasonic detection of surface-breaking railhead defects
Rachel S Edwards, Mayorkinos Papaelias, Caroline Holmes, Yichao Fan, Steve Dixon, Claire L Davis, Clive Roberts and Bruce Drinkwater
On the UK rail network, changing usage patterns mean that gauge corner cracking in the railhead is a problem, and frequent testing for such defects is essential. These defects are currently managed through rail grinding. Existing systems used on the UK rail network for detecting surface breaking defects are limited in speed (< 30 mph) and accuracy (> 5 mm).
We are currently working on novel ultrasonic methods of detecting gauge corner cracking, and will present details of these measurements. A novel pitch-catch ultrasonic system comprising of two electro-magnetic acoustic transducers (EMATs) generating and detecting Rayleigh waves has the potential to operate at higher speed, improving network inspection coverage. This system detects signals and performs an FFT in less than 1 ms, and changes in the detected signal amplitude and frequency content are used to characterise defects. A new set of simulated defects on sections of rail have been produced, including half-face slots machined normal to the railhead surface, clusters of angled slots, and pocket defects more typical of real defects. The smallest pocket defects are difficult to detect, with changes in signal amplitude and cutoff falling close to the noise level. However, at chosen higher frequencies a drop in FFT magnitude indicates the presence of a defect, and this indicator can be logically combined with amplitude and cutoff measurements to provide a more reliable result. Further ongoing developments involve evaluation of phased array ultrasonic techniques and their potential for giving detailed information about such cracking.
Probability of detection for far end ultrasonic axle testing
John R Rudlin and Charles R A Schneider
TWI, Cambridge CB1 6AL, UK. T: 01223 899000; F: 01223 890952; E: john.rudlin@twi.co.uk
Inspection of wheel set axles from the far end has been common practice in the UK rail industry for many years. Recently the value of such inspections has been questioned because of a perceived difficulty with the inspection and a suspicion that there is poor sensitivity to defects. The WIDEM project has included a work package to investigate this sensitivity experimentally. This paper describes the method, the experimental work and the estimated probability of detection (POD) curves for various probe types. Statistical tests are used to assess the adequacy of different statistical models for the POD and to identify factors that have a significant influence on the inspection reliability. The implications of the results are discussed.
