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Comparison of NDT-methods for automatic inspection of weld defects
University West, Department of Engineering Science, Division of Process and Product Development. (PTW)ORCID iD: 0000-0001-7748-0565
University West, Department of Engineering Science. (PTW)
University West, Department of Engineering Science, Division of Process and Product Development. (PTW)ORCID iD: 0000-0001-6933-375X
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.

Place, publisher, year, edition, pages
2015. Vol. 50, no 1, 1-21 p.
Keyword [en]
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: urn:nbn:se:hv:diva-3113DOI: 10.1504/IJMPT.2015.066863ISI: 000352133300001Scopus ID: 2-s2.0-84921311226OAI: oai:DiVA.org:hv-3113DiVA: diva2:392434
Projects
ANDTE
Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2016-02-08Bibliographically approved
In thesis
1. Towards Automation of Non-Destructive Testing of Welds
Open this publication in new window or tab >>Towards Automation of Non-Destructive Testing of Welds
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

All welding processes can give rise to defects that will weaken the joint and can lead to failure of the welded structure. Because of this, non-destructive testing (NDT) of welds have become increasingly important to ensure the structural integrity when the material becomes thinner and stronger and welds become smaller; all to reduce weight in order to save material and reduce emissions due to lighter constructions.

Several NDT methods exists for testing welds and they all have their advantages and disadvantages when it comes to the types and sizes of defects that are detectable, but also in the ability to automate the method. Several methods were compared using common weld defects to determine which method or methods were best suited for automated NDT of welds. The methods compared were radiography, phased array ultrasound, eddy current, thermography and shearography. Phased array ultrasound was deemed most suitable for detecting the weld defects used in the comparison and for automation and was therefore chosen to be used in the continuation of this work. Thermography was shown to be useful for detecting surface defects; something not easily detected using ultrasound. A combination of these techniques will be able to find most weld defects of interest.

Automation of NDT can be split into two separate areas; mechanisation of the testing and automation of the analysis, both presenting their own difficulties. The problem of mechanising the testing has been solved for simple geometries but for more general welds it will require a more advance system using an industrial robot or similar. Automation of the analysis of phased array ultrasound data consists of detection, sizing, positioning and classification of defects. There are several problems to solve before a completely automatic analysis can be made, including positioning of the data, improving signal quality, segmenting the images and classifying the defects. As a step on the way towards positioning of the data, and thereby easing the analysis, the phase of the signal was studied. It was shown that the phase can be used for finding corners in the image and will also improve the ability to position the corner as compared to using the amplitude of the signal. Further work will have to be done to improve the signal in order to reliably analyse the data automatically.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2011. 42 p.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keyword
Welding, non-destructive testing, NDT
National Category
Computer Vision and Robotics (Autonomous Systems) Fluid Mechanics and Acoustics Applied Mechanics
Research subject
ENGINEERING, Industrial engineering
Identifiers
urn:nbn:se:hv:diva-4122 (URN)978-91-7439-352-1 (ISBN)
Presentation
2011-12-19, E246, Luleå tekniska universitet, Luleå, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2012-02-08 Created: 2012-02-02 Last updated: 2016-02-08Bibliographically approved
2. Imaging and analysis methods for automated weld inspection
Open this publication in new window or tab >>Imaging and analysis methods for automated weld inspection
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
Welding, materials
National Category
Materials Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-6696 (URN)978-91-7439-931-8 (ISBN)978-91-7439-932-5 (ISBN)
Opponent
Available from: 2014-09-17 Created: 2014-09-17 Last updated: 2016-02-08Bibliographically approved

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