Time-of-flight diffraction ultrasonics

About: Time-of-flight diffraction ultrasonics is a research topic. Over the lifetime, 544 publications have been published within this topic receiving 3189 citations.

Method for estimating fatigue propagation life of intermittent sandwich steel plate

Abstract: The invention discloses a method for estimating fatigue propagation life of an intermittent sandwich steel plate based on the TOFD (Time of Flight Diffraction) technology and the fracture mechanics theory. An initial flaw size in calculation parameters of the fracture mechanics theory has great influence on fatigue propagation process, so that the measurement accuracy of an initial flaw length has influence on the accuracy of an estimation result when estimating the fatigue propagation life by using the fracture mechanics theory; since the TOFD is extremely high in flaw measurement accuracy being +/- 0.3mm parallel to an acoustic beam, the size of the intermittent sandwich flaw measured by using the TOFD technology is taken as the initial flaw length calculated by using the fracture mechanics theory; other parameters calculated by using the fracture mechanics theory are obtained by cutting, sampling and manufacturing a steel plate with the intermittent sandwich flaw into a test piece for carrying out fatigue test; by utilizing the fracture mechanics theory, the fatigue propagation life of a boiler steel structure with the intermittent sandwich flaw is estimated. The method is accurate in measurement.

Pod Generator Project, a Numerical Assessment of the Inspection of Fatigue Cracks Using Tofd

Abstract: Risk based inspection strategies rely on detailed knowledge of the performance of inspection techniques. The objective of the “POD generator” project is to develop a numerical modeling approach to assess the effectiveness of specific inspection techniques. Simulation offers flexibility and reliability at acceptable costs. Therefore numerical models have been developed and validated for accurately simulating the physics of inspection techniques. These numerical models are then used to generate quantitative probability of detection (POD) curves. In the case of ultrasonic time‐of‐flight‐diffraction (TOFD) inspections, the human factor is included on two levels. First in the way a TOFD scan is carried out (positioning variations). And secondly, in the fact that simulated inspection results are interpreted by real operators. This paper shows the assessment of the inspection of fatigue cracks using TOFD using this numerical approach. The influence of high‐low and the human interpretation on the performance of the inspection was investigated by generating multiple POD‐curves under different circumstances. This way we show that the numerical modeling approach is an efficient and reliable way of determining the sensitivity of inspection techniques for complex influencing factors.

Monitoring heights of defects in welds using the ultrasonic time-of-flight diffraction technique

Abstract: SUMMARY The Time-of-Flight Diffraction (TOFD) technique has been used to monitor the heights of defects in welds of a vessel that has been in operation for 25 years. Regular monitoring of defect height provides a check that the defects are stable. Satisfactory results mean that the vessel can be kept in operation for a further period. The TOFD technique has been selected for its high sizing accuracy, as this allows a high level of reproducibility to be achieved. This presentation will describe the approach to this monitoring problem, as well as the preparations and the formulation of the criteria used to judge future results on the presence of growth.

Design of Ultrasonic Probe Configuration Using Finite-Difference Time Domain Simulation

Abstract: An analysis tool has been developed for optimizing ultrasonic transmitter-receiver configurations for in-situ monitoring of crack propagation during cyclic loading in order to develop better crack tip models for fatigue life estimation. Time-of-flight diffraction technique is simulated using finite-difference time-domain method to study the interaction of ultrasonic waves from probes with defects/cracks. Governing equations relating velocities to stresses are discretized using central finite-difference formulation and solved on a staggered grid in an explicit time-marching scheme, with velocity and stress components offset in time and space. This leads to a leap frog scheme in which the velocity and stress components are calculated alternately from each other. Grid size is taken as the ratio of minimum wavelength and number of steps per wavelength \((N = \text {15} -\text {20})\) to ensure stability. Time step is obtained from Courant stability criteria. Defect surface is modelled as traction-free. Perfectly matching layer with small damping factor is applied to minimize the amplitude of waves reflected from boundaries created at the edges of domain. Simulation matches well with results from finite element model using ABAQUS / EXPLICIT solver. FDTD method can be used for designing optimum transmitter-receiver configuration since it is computationally less expensive and easy to implement as compared to FEM.

Device for TOFD (time of flight diffraction) and phased array integrated detection of hot melt butt joint of polyolefin pipeline

Abstract: The invention relates to a detection technology of a hot melt butt joint of a polyolefin pipeline and aims at providing a device for TOFD (time of flight diffraction) and phased array integrated detection of a hot melt butt joint of a polyolefin pipeline. The device comprises two phased array ultrasonic probes, two holding devices, two circumferential motion scanning devices, and two probe frame and coupling devices, wherein the holding devices clamp the polyolefin pipeline in a surrounding manner and are used for mounting the circumferential motion scanning devices; the two ends of a connecting rod are connected with mounting platforms of the circumferential motion scanning device respectively via mounting frames; the two probe frame and coupling devices are mounted in the middle of the connecting rod; the bottoms of the coupling devices are placed on the polyolefin pipeline; the two phased array ultrasonic probes are oppositely mounted on oblique surfaces of hollow containers; and ultrasonic transmission directions of the phased array ultrasonic probes are intersected below a position between the ultrasonic probes. The phased array ultrasonic probes can achieve omnibearing detection of the hot melt butt joint; a shape feature of a defect can be accurately positioned; and a non-fusion defect of the hot melt joint is detected and evaluated completely.