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Imaging and analysis methods for automated weld inspection
University West, Department of Engineering Science, Division of Automation Systems. (PTW)ORCID iD: 0000-0001-7748-0565
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

All welding processes can give rise to defects, which weakens the joint and can eventually lead to the failure of the welded structure. In order to inspect welds for detects, without affecting the usability of the product, non-destructive testing (NDT) is needed. NDT includes a wide range of different techniques, based on different physical principles, each with its advantages and disadvantages. The testing is often performed manually by a skilled operator and in many cases only as spot-checks. Today the trend in industry is to move towards thinner material, in order to save weight for cost and for environmental reasons. The need for inspection of a larger portion of welds therefore increases and there is an increasing demand for fully automated inspection, including both the mechanised testing and the automatic analysis of the result. Compared to manual inspection, an automated solution has advantages when it comes to speed, cost and reliability. A comparison of several NDT methods was therefore first performed in order to determine which methods have most potential for automated weld inspection. Automated analysis of NDT data poses several difficulties compared to manual data evaluation. It is often possible for an operator to detect defects even in noisy data, through experience and knowledge about the part being tested. Automatic analysis algorithms on the other hand suffer greatly from both random noise as well as indications that originate from geometrical variations. The solution to this problem is not always obvious. Some NDT techniques might not be suitable for automated inspection and will have to be replaced by other, better adapted methods. One such method that has been developed during this work is thermography for the detection of surface cracks. This technique offers several advantages, in terms of automation, compared to existing methods. Some techniques on the other hand cannot be easily replaced. Here the focus is instead to prepare the data for automated analysis, using various pre-processing algorithms, in order to reduce noise and remove indications from sources other than defects. One such method is ultrasonic testing, which has a good ability for detecting internal defects but suffers from noisy signals with low spatial resolution. Work was here done in order to separate indications from corners from other indications. This can also help to improve positioning of the data and thereby classification of defects. The problem of low resolution was handled by using a deconvolution algorithm in order to reduce the effect of the spread of the beam.The next step in an automated analysis system is to go beyond just detection and start characterising defects. Using knowledge of the physical principles behind the NDT method in question and how the properties of a defect affect the measurement, it is sometimes possible to develop methods for determining properties such as the size and shape of a defect. This kind of characterisation of a defect is often difficult to do in the raw data, and is therefore an area where automated analysis can go beyond what is possible for an operator during manual inspection. This was shown for flash thermography, where an analysis method was developed that could determine the size, shape and depth of a defect. Similarly for laser ultrasound, a method was developed for determining the size of a defect.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology , 2014. , viii, 68 s. p.
Series
Doctoral thesis / Luleå University of Technology, ISSN 1402-1544
Keyword [en]
Welding, materials
National Category
Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-6696ISBN: 978-91-7439-931-8 (print)ISBN: 978-91-7439-932-5 (print)OAI: oai:DiVA.org:hv-6696DiVA: diva2:747572
Opponent
Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2016-02-08Bibliographically approved
List of papers
1. Comparison of NDT-methods for automatic inspection of weld defects
Open this publication in new window or tab >>Comparison of NDT-methods for automatic inspection of weld defects
2015 (English)In: International journal of materials & product technology, ISSN 0268-1900, E-ISSN 1741-5209, Vol. 50, no 1, 1-21 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study is to investigate different NDT-methods for weld inspection in an objective manner. Test objects are produced with known variation of flaws: internal pores, surface and internal cracks, toe radius and weld depth. The NDT-methods compared are: phased array ultrasound, radiography, eddy current, thermography and shearography. The results show that radiography is the better method for volumetric defects in thin plates while ultrasound is better for flat defects and thicker, non-flat plates. Thermography was shown to have a good ability of detecting surface defects. A combination of ultrasound and thermography results in a detection of all the non-geometrical defects investigated in this study.

Keyword
non-destructive testing, NDT, weld defects, automatic inspection
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-3113 (URN)10.1504/IJMPT.2015.066863 (DOI)000352133300001 ()2-s2.0-84921311226 (Scopus ID)
Projects
ANDTE
Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2016-02-08Bibliographically approved
2. Improved Image Quality in Phased Array Ultrasound by Deconvolution
Open this publication in new window or tab >>Improved Image Quality in Phased Array Ultrasound by Deconvolution
2012 (English)In: 18th World Conference on Nondestructive Testing: 16-20 April 2012, Durban, South Africa, 2012, 1-5 pdf. p.Conference paper, (Refereed)
Abstract [en]

High contrast and resolution in phased array ultrasonic images are of importance for accurate evaluation. The spread of the ultrasonic beam is one cause of the images being unsharp. One technique for reducing the influence of the beam spread, and thereby improving the image quality, is by deconvolving the data with the point spread function of the ultrasonic beam. By assuming that the material is homogeneous, the point spread function of the beam can be simulated using diffraction theory. Results from a deconvolution performed on data acquired from a side drilled hole in a steel calibration block are presented. It is shown that a significant improvement in sharpness and contrast can be achieved.

Keyword
ultrasound, phased array, image quality, deconvolution, point spread function
National Category
Signal Processing
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4142 (URN)
Conference
18th World Conference on Non-Destructive Testing
Available from: 2012-04-23 Created: 2012-02-10 Last updated: 2016-02-08Bibliographically approved
3. Improved Corner Detection by Ultrasonic Testing using Phase Analysis
Open this publication in new window or tab >>Improved Corner Detection by Ultrasonic Testing using Phase Analysis
2013 (English)In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 53, no 2, 630-634 p.Article in journal (Refereed) Published
Abstract [en]

In ultrasonic testing, corners are used for sensitivity calibration in the form of notches, for measuring the sound velocity in the material, and as known reference points during testing. A 90° corner will always reflect incoming waves in the opposite direction due to a double reflection and therefore give a strong echo. This article presents a method for separating the echo from a corner from other echoes and more accurately find the position of the corner. The method is based on analysing the phase of the reflected signal. The proposed method was tested on a steel calibration block and the width of the indication was reduced by up to 50% compared to the amplitude signal. This results in a more accurate positioning of the corner. Using the phase instead of the amplitude will also improve the reliability, since reflections other than from corners will disappear.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
phase, ultrasound, non-destructive testing, corner, calibration, WIL, Work-integrated Learning, AIL
National Category
Signal Processing
Research subject
ENGINEERING, Physics; Work Integrated Learning
Identifiers
urn:nbn:se:hv:diva-4112 (URN)10.1016/j.ultras.2012.10.015 (DOI)000311488800039 ()2-s2.0-84870250647 (Scopus ID)
Projects
ANDTE
Available from: 2012-01-26 Created: 2012-01-26 Last updated: 2016-02-08Bibliographically approved
4. Sizing of subsurface defects in thin walls using laser ultrasonics
Open this publication in new window or tab >>Sizing of subsurface defects in thin walls using laser ultrasonics
2014 (English)Article in journal (Refereed) Submitted
Abstract [en]

Laser ultrasonics is a non-destructive testing technique where a focused laser is used for generating an ultrasound pulse and a second laser is used for detection. This ultrasound pulse is used for detecting surface or near surface defects. A defect will not only reflect the incoming surface wave, but also alter the frequency contents of the transmitted wave. When the detection laser was scanned along the surface, changes in frequency contents of the sound pulse were detected and could be analysed to give information about the diameter of the defect.

Keyword
Laser ultrasonics, Rayleigh waves, additive manufacturing, defect sizing
National Category
Mechanical Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-6695 (URN)
Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2016-02-08Bibliographically approved
5. Analysis method for pulsed thermography based on an analytical solution of the heat equation
Open this publication in new window or tab >>Analysis method for pulsed thermography based on an analytical solution of the heat equation
2014 (English)Article in journal (Refereed) Submitted
Abstract [en]

An analytical solution to the heat equation is presented, using a simplified physical model of pulsed thermography. This solution was compared to experimental data and showed good correlation, with r=0.97. An analysis method for sizing and determining the depth of a defect was developed using this analytical solution. The shape of the defect was estimated using deconvolution. Results from thermography tests on flat bottom holes show the possibilities of the method to determine the size, shape and depth of the defect, if the physical properties of the material are known.

Keyword
Pulsed thermography; defect shape reconstruction; analytic solution; deconvolution
National Category
Mechanical Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-6694 (URN)
Note

Ingår i författarens avhandling.

Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2016-02-08Bibliographically approved
6. Surface crack detection in welds using thermography
Open this publication in new window or tab >>Surface crack detection in welds using thermography
2013 (English)In: NDT & E international, ISSN 0963-8695, E-ISSN 1879-1174, Vol. 57, 69-73 p.Article in journal (Refereed) Published
Abstract [en]

Thermography is today used within non-destructive testing for detecting several different types of defects. The possibility for using thermography for detecting surface cracks in welded metal plates has here been investigated. During testing the weld is illuminated using a high power infrared light source. Due to surface cracks acting like black bodies, they will absorb more energy than the surrounding metal and can be identified as a warmer area when imaged using an infrared camera. Notches as well as real longitudinal cold cracks in a weld are investigated using the presented method. The results show that thermography is promising as a method for detection cracks open to the surface.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Thermography, Surface flaw, Welding, Crack, work-integrated learning, WIL, AIL
National Category
Production Engineering, Human Work Science and Ergonomics Metallurgy and Metallic Materials
Research subject
ENGINEERING, Physics; Work Integrated Learning
Identifiers
urn:nbn:se:hv:diva-4830 (URN)10.1016/j.ndteint.2013.03.008 (DOI)000319848500009 ()2-s2.0-84877761561 (Scopus ID)
Available from: 2013-05-03 Created: 2012-11-26 Last updated: 2016-02-08Bibliographically approved

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