The detection and measurement of overlapping fatigue cracks at welded joints by thin-skin electromagnetic fields

1988 ◽  
Vol 419 (1856) ◽  
pp. 69-89 ◽  
Keyword(s):  
Measurement Method ◽  
Fatigue Cracks ◽  
Current Field ◽  
Welded Steel ◽  
Non Destructive Evaluation ◽  
Thin Skin ◽  
Response Profiles ◽  
Steel Joints ◽  
Non Destructive ◽  
Probe Response

Fatigue cracks occur at different locations at the toes of welded steel joints. With continued load cycling it is often found that the cracks grow towards each other and overlap in adjacent parallel planes. It is useful to be able to detect and measure overlapping cracks and in this paper the characteristic responses to be expected from these features are calculated for the alternating-current field-measurement method of non-destructive evaluation by thin-skin theory. Typical signal profiles are calculated for probe traverses across the cracks and parallel to the edges. These are compared with experimental data obtained by using three pairs of overlapping notches with different proportions, cut in a steel block. The notches were interrogated by a thin-skin field at a frequency of 6 kHz. The calculations show that overlapping cracks give rise to asymmetric cross-crack signal profiles, which do not occur for single cracks, and to characteristic changes in curvature in the probe response profiles. These features are well confirmed by the experiments. The results also show that traverses along the crack edges can be used to find the positions of the crack ends.

scholarly journals Optimisation of amplitude distribution of magnetic Barkhausen noise

2017 ◽  
Vol 68 (5) ◽  
pp. 384-389
Author(s):  
Jozef Pal’a ◽  
Vladimír Jančárik
Keyword(s):  
Measurement Method ◽  
Measurement Accuracy ◽  
Amplitude Distribution ◽  
Barkhausen Noise ◽  
Significant Issue ◽  
Magnetic Barkhausen Noise ◽  
Non Destructive Evaluation ◽  
Treatment Conditions ◽  
Lift Off ◽  
Non Destructive

Abstract The magnetic Barkhausen noise (MBN) measurement method is a widely used non-destructive evaluation technique used for inspection of ferromagnetic materials. Besides other influences, the excitation yoke lift-off is a significant issue of this method deteriorating the measurement accuracy. In this paper, the lift-off effect is analysed mainly on grain oriented Fe-3%Si steel subjected to various heat treatment conditions. Based on investigation of relationship between the amplitude distribution of MBN and lift-off, an approach to suppress the lift-off effect is proposed. Proposed approach utilizes the digital feedback optimising the measurement based on the amplitude distribution of MBN. The results demonstrated that the approach can highly suppress the lift-off effect up to 2 mm.

Influence of inspection on the safety of fatigue loaded welded cruciform steel joints – comparison of simplified and advanced crack growth models

2021 ◽  
Author(s):  
Davide Leonetti ◽  
Johan Maljaars ◽  
Bert Snijder
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Prediction Models ◽  
Growth Models ◽  
Fatigue Cracks ◽  
Welded Steel ◽  
Short Cracks ◽  
Proposed Model ◽  
Recent Developments ◽  
Steel Joints

<p>Probabilistic fatigue life prediction models of welded steel joints are often used to estimate the level of safety, which is given in terms of the probability of failure or the reliability index as a function of the applied load cycles. Prediction models based on fracture mechanics allow taking into account the effect of inspections on the estimated level of safety. Recent developments in fracture mechanics based fatigue prediction models allow modeling the behavior of short and long fatigue cracks under constant and variable amplitude loading. Short cracks are relevant since their growth characterizes most of the fatigue life, especially under service loading. A recently proposed model by the authors is considered and compared to a more traditional and simplified model as proposed in the standard BS7910, where no distinction is made between short and long cracks. The effect of the model uncertainty, the type of inspection, and the time of the inspection on the estimated level of safety are quantified for welded cruciform steel joints.</p>

scholarly journals An Experimental Study of Damage Detection on Typical Joints of Jackets Platform Based on Electro-Mechanical Impedance Technique

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7168
Author(s):  
Liaqat Ali ◽  
Sikandar Khan ◽  
Naveed Iqbal ◽  
Salem Bashmal ◽  
Hamad Hameed ◽  
...  
Keyword(s):  
Mechanical Impedance ◽  
Offshore Structures ◽  
Theoretical Background ◽  
Welded Steel ◽  
Electromechanical Impedance ◽  
Impedance Technique ◽  
Jacket Structures ◽  
Average Variance ◽  
Steel Joints ◽  
Non Destructive

Many methods have been used in the past two decades to detect crack damage in steel joints of the offshore structures, but the electromechanical impedance (EMI) method is a comparatively recent non-destructive method that can be used for quality monitoring of the weld in structural steel joints. The EMI method ensures the direct assessment, analysis and particularly the recognition of structural dynamics by acquiring its EM admittance signatures. This research paper first briefly introduces the theoretical background of the EMI method, followed by carrying out the experimental work in which damage in the form of a crack is simulated by using an impedance analyser at different distances. The EMI technique is used to identify the existence of damage in the welded steel joints of offshore steel jacket structures, and Q345B steel was chosen as the material for test in the present study. Sub-millimetre cracks were found in four typical welded steel joints on the jacket platform under circulating loads, and root average variance was used to assess the extent of the crack damage.

Non destructive evaluation of concrete contamination by chloride. Comparison of methods

2011 ◽  
Vol 15 (7) ◽  
pp. 1073-1084
Author(s):  
Jean-Paul Balayssac ◽  
Stéphane Laurent ◽  
Gilles Klysz ◽  
Jean-François Lataste ◽  
Xavier Derobert
Keyword(s):  
Comparison Of Methods ◽  
Non Destructive Evaluation ◽  
Non Destructive
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