Sizing Of Surface-breaking Cracks Research Articles

An arrayed uniform eddy current probe design for crack monitoring and sizing of surface breaking cracks with the aid of a computational inversion technique

This study demonstrates that eddy current testing can be an effective method for monitoring the growth of surface breaking cracks with the aid of computational inversion techniques. A uniform eddy current probe with 23 arrayed detectors was designed, and pseudo monitoring tests were carried out to measure signals due to six mechanical fatigue cracks introduced into type 316L austenitic stainless steel plates. In the test the position of the probe was fixed to simulate monitoring. The depths of the cracks were evaluated using a computational inversion method developed on the basis of k-nearest neighbor algorithm. The depths of the mechanical fatigue cracks whose actual depths were 1.1, 2.1, 3.1, 5.5, 6.7, and 8.5mm were evaluated to be 0.9, 1.9, 3.8, 4.3, 7.0, and 5.7mm, respectively. Additional simulations were conducted to demonstrate the stability of the method.

Recent research and development activities in electromagnetic sensor technologies

TSC designs and builds electromagnetic sensor probes for the industrial NDT market. These probes are used for the detection and sizing of surface-breaking cracks in metals and for the determination of stresses in steel. The company expends a great deal of effort in research and development; this R&D typically consists of numerical simulations and the creation of prototype probes. This paper details the research and development of some of the more complex probes TSC has recently created.

Reliability assessment of manual ultrasonic time of flight diffraction (TOFD) inspection for complex geometry components

Experimental probability of detection (POD) and probability of sizing (POS) curves are developed for the detection and sizing of surface-breaking cracks in components having complex geometry. A manual ultrasonic time of flight diffraction (TOFD) inspection system has been used to develop these POD and POS curves. Initially, it was assumed and subsequently verified that signal responses have a normal distribution. The effects of probe angle and probe center-to-center spacing on both POD and POS were observed. Unlike the PODs previously reported for conventional ultrasonic amplitude based flaw sizing techniques, the PODs associated with TOFD in the range of defect sizes considered here, exhibit a decreasing trend for a fixed set of experimental parameters. It is important to emphasize that the curves obtained in this work are specific to the geometry, specimen dimensions, set of notches and the specific probes used in the experiment. However, when using a manual TOFD inspection system, these curves can be useful for planning the risk-based inspection of components having complex geometry (such as a steam turbine rotor shaft).

Sizing of surface-breaking cracks in complex geometry components by ultrasonic Time-of-Flight Diffraction (TOFD) technique

Sizing a surface-breaking crack in a complex geometry component, for example a steam turbine's solid rotor shaft, is a challenging inspection task. This paper deals with experimental work for the evaluation of the Time-of-Flight Diffraction (TOFD) technique for sizing of surface-breaking cracks in such a complex geometry component. The experimental results show that with the help of the mathematical model explained here, TOFD can size such cracks with reasonable accuracy.

Eddy Current Examination of Fatigue Cracks in Inconel Welds

Basic studies on the eddy current examination of defects in Inconel, a typical nickel-base alloy used in the reactor vessel, pressurizer, and core internal of nuclear power plants, are carried out. The detecting and sizing capability of the eddy current method is investigated through analytical and experimental approaches. Probe’s detectability is numerically evaluated, and appropriate probe and examination conditions are correspondingly selected. The numerical signal calculation and crack reconstruction approach is confirmed in terms of the study of the eddy current examination of electrodischarge machining notches in Inconel base metal, and further applied to eddy current examination of fatigue cracks in Inconel welds. The profiles of fatigue cracks are reconstructed using eddy current testing signals. Crack depths estimated by eddy current reconstruction agree well with that of ultrasonic testing and are consistent with the crack depths revealed from destructive testing. The research presented in this paper shows that by choosing a proper testing situation, eddy current examination is feasible for detecting and sizing of surface-breaking cracks in Inconel welds.

Detection of Surface Breaking Cracks in Concrete Members Using Rayleigh Waves

This study examines the use of Rayleigh waves for the detection and sizing of surface-breaking cracks in concrete members. First, finite element simulations are performed to define the conditions for Rayleigh wave propagation in members with rectangular cross-section followed by an experimental study with a concrete beam. Time histories recorded at different locations are 2D Fourier transformed into the frequency-wavenumber domain to enhance interpretation and data analysis. Rayleigh waves form at depths less than half the beam depth. With the introduction of a slot, Rayleigh waves are not observed behind the slot, except for the shortest slot depth, and the slot depth cannot be estimated in the frequency-wavenumber domain. Autospectrum calculations reveal strong Rayleigh wave reflections in front of the slot and by can be used to estimate slot depth when the wavelength is less than half the beam depth.

Application of the ACFM inspection method to rail and rail vehicles

The ACFM inspection technique is an electromagnetic inspection method, which is widely used in the oil and gas industry for the detection and sizing of surface-breaking cracks. It provides a number of advantages over conventional inspection methods, particularly in the ability to inspect without removing coatings or grease, and has recently been adapted for a number of specific rail applications. The technique has now been accredited in the UK for use on vehicle wheelsets and for the inspection of plain rail. This paper describes the background to the ACFM technique and its application to in-service inspection. The development of a new 'Walking Stick'for inspection of the rail head is described, together with some of the challenges of inspecting the complex crack geometries associated with cracks generated by rolling contact fatigue (RCF). ACFM has also been applied to both plain and driven axles: examples of these applications together with its use on bogies are also given. This paper also considers some of the challenges faced when transferring technology from one industry to another. Operator training has to be considered as well as the validation requirements for acceptance of a new technique. Validation often requires comparison with existing technologies in blind trials but these are not necessarily quantitative in terms of performance. Destructive sectioning provides an absolute measure of system capability and was also used during these developments. Results from both destructive and non-destructive trials are discussed.

Modeling for quantitative non-destructive evaluation

A quantitative approach to non-destructive evaluation (NDE) must be based on models of the measurement processes. A model's purpose is to predict, from first principles, the measurement system's response to material properties and anomalies in a material or structure. For the ultrasonic case a measurement model should include modeling of the generation, propagation and reception of ultrasonic signals, and the ultrasonic interactions that generate the system's response function. A measurement model has many benefits, which are discussed in the paper. Three examples of the productive use of quantitative modeling in conjunction with measured data are presented: the detection and sizing of fatigue cracks which emanate from weep holes in the risers of wing panels in the interior of an aircraft wing by the use of ultrasound generated on the exterior surface of the wing, the determination of the elastic constants of anisotropic thin films deposited on a substrate, and the detection and sizing of surface-breaking cracks by the use of the laser-source scanning technique for laser generated and detected ultrasound.

Surface magnetic field measurement technique for nondestructive testing of metals

The Letter explains the principles of a new electromagnetic technique, the surface magnetic field measurement technique (SMFM), for the detection and sizing of surface-breaking cracks in metals. The signals associated with circular-arc cracks are examined and techniques for inverting crack signals to crack dimensions, are outlined.

Surface potential distributions due to eddy currents around long cracks in metals, induced by U-shaped current-carrying wires

Sizing of surface-breaking cracks in metals by the AC field measurement (ACFM) technique by producing the surface field by inducing current into the specimen under test is considered. The surface potential distribution produced by an inducing mechanism around a long crack in a ferrous metal is formulated, and the crack signal, which is the variation of the potential difference around the crack, is investigated by varying the crack depth, the dimensions of the inducer, and the inducer's lift-off distance from the metal surface. The inducer consists of two parallel U-shaped wires symmetrically attached to the two sides of an ACFM probe. It is shown that the direct application of the one-dimensional formula based on the uniform field assumption for the interpretation of the crack signal gives rise to an underestimation of the crack depth. However, it is shown that the error in depth measurement by this formula can be negligible if the horizontal sections of the inducer's wires are sufficiently long.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>