Guided Wave Focusing Mechanics in Pipe

Guided waves can be used in pipe inspection over long distances. Presented in this paper is a beam focusing technique to improve the S/N ratio of the reflection from a tiny defect. Focusing is accomplished by using non-axisymmetric waveforms and subsequent time delayed superposition at a specific point in a pipe. A semi-analytical finite element method is used to present wave structure in the pipe. Focusing potential is also studied with various modes and frequencies.

Evaluation of WB Coatings by Scanned Imaging Microscopy

Organic thick coatings (epoxy, polyurethane, and acrylic-urethane) have been widely applied to high modulus substrates (e.g., steel) for anticorrosion protection. To improve performance, reinforced components (clay, bochmite, nanopaticles, etc.) are usually added to these coatings. However, the acoustic evaluation of these coatings is difficult due to their low acoustic velocities and high attenuation coefficients. In this paper, first, the scanning acoustic microscope (SAM) is used to image sub-surfaces, coating/substrate interfaces, and to measure acoustic velocities. Different phases can be observed on some coatings and defects can be found at some interfaces. Secondly, the atomic force microscope (AFM) is applied to image surfaces at high resolution (compared to SAM). These results agree with SAM images. Thirdly, a nano-indentation technique is utilized to measure the reduced Young’s modulus and absolute hardness of the coatings. The results show that epoxy has the highest Young’s modulus and acrylic-urethane has the lowest. Reinforced components can either increase or decrease Young’s modulus, and hardness depending on the coating material. Finally, results from the SAM, AFM and nano-indentation are compared and analyzed to optimize the evaluation.

Scattering From Voids in Solids in the Intermediate Wavelength Regime

The main objective of this work was to develop techniques of non-destructive testing and give them a strong theoretical underpinning to render them as quantitative as possible. Thus in ultrasonic testing the objective was to combine the traditional manual search for flaws with computer automated search and elastic scattering theory to provide quantitative data on location, size, shape, and orientation. This approach led to several schemes to solve the Inverse Scattering Problem or the reconstruction of a flaw from just a few reflected ultrasonic echoes. Early efforts led to successes with idealized man-made flaws consisting of single and compound flaws embedded in Titanium-alloy. Later this work produced results with naturally occurring flaws in aerospace components.

Micro-Structural Monitoring of 2.25Cr-1Mo Steel by Surface SH Wave

The feasibility of SH (shear horizontal) waves for monitoring thermally degraded materials is explored. It turns out that the use of SH waves leads to a promising nondestructive technique for the purpose of microstructure evaluation and material characterization of such materials. This is because SH modes can interact with entire surface and subsurface area of specimen that is mainly exposed to severe thermal environment, while a conventional point-by-point technique is confined to just local investigations, underneath a transducer. Consequently, SH modes’ data can show a better sensitivity and provide us with various features for thermal damage evaluation, compared to ones of local inspection, which results in the enhancement of experimental reliability. 2.25Cr-1Mo steel specimens for various degradation levels were prepared by isothermal aging heat treatment at 650° and evaluated by the present technique to investigate the influence of thermal damage to the SH wave feature based on the attenuation coefficients. Discussed is monitoring for thermally degraded structural materials used at high temperature by the surface SH-wave propagating along near surface and subsurface layer with horizontal displacement polarization. Because of the carbide precipitation increase and spheroidization near the grain boundary of a microstructure to aging degradation, the attenuation coefficient had a tendency to increase as degradation proceeded. It was identified possibly to evaluate degradation using the characteristics of the attenuation coefficient and amplitude spectra through Fast Fourier Transform (FFT) analysis. Frequency dependence of the ultrasonic attenuation coefficient to aging degradation appeared large, which made sure that the attenuation coefficient can be an important parameter for the evaluation of aging.

Acoustic Microscopy for Evaluating Cracks Produced by CO2 Laser Within Thin Alumina Plates

The laser shaping of thin alumina ceramic plates appears to be an advantageous manufacturing method. Unfortunately, the failure rate for using this technique is high because of crack initiation during the application of a high power laser. We address the issue of crack initiation with the use of in-process and post-process analysis. This article reports our results on the evaluation of the surface and interior cracks with optical, scanning laser, scanning electron and scanning acoustic microscopy. We present images of surface and subsurface micro-cracks generated at different power levels of a high power CO2 laser system. The spatial variation of the Rayleigh wave velocity is measured by the V(z) curve technique. These preliminary data suggest that, some with improvement, the V(z) technique may detect residual stress with high spatial resolution. The obtained results may contribute to the understanding of the fracture mechanism, and can eventually provide guidance for the choice of laser parameters (e.g., power, focus, scanning rate, emitting duration, or the like) in laser shaping apparatus.

Stress and Temperature Effects on Ultrasonic Properties in Cross Linked and High Density Polyethylene

Cross linked polyethylene is widely used in the manufacturing of tanks for the agriculture, petroleum and chemical industries. These tanks are exposed to a number of environmental effects, which can lead to material degradation. Ultrasonic wave speed change is a method that shows promise in evaluating the UV degradation effects. In order to evaluate the UV effects in the field, however, the effect of stress and temperature on the wave speed must first be established. A series of tests were performed to establish the ultrasonic properties in cross linked as well as natural polyethylene at a range of temperatures from −6 deg C to 44 deg C (22 deg F to 112 deg F). The change is linear, as expected. For the stress tests, the velocity decreased with tension, also as expected. Tests were performed from approximately 689 kPa to 9.6 MPa (100 psi to 1400 psi). Results from these tests were incorporated into the overall algorithm used for evaluating tank degradation.

Characterization of Moon Rock Media With Elastic Waves

Elastic wave propagation in porous media will be introduced by a discussion of scattering to show the use of broad frequency band pulses in relating the attenuation, velocity and backscattering to information on porosity. Examples will be given for microporosity in castings and powder metal components. This will be followed by a discussion of the influence of volatiles within the pores on the absorption of elastic waves in porous ceramics and rocks. Implications of these findings will be given for ultrasonic device applications and for the interpretation of the lunar seismic experiments carried out as part of the Apollo missions to the moon.

Natural Focusing for the Detection of Defects Beyond Elbows

Long range ultrasonic guided wave inspection is advancing rapidly and is commonplace today. Benefits of using longitudinal or torsional modes are being established in special circumstances of improved sensitivity, resolution, or penetration power. The possibility of inspection under insulation, coatings, or with water filled pipes or around elbows is possible. Detection of defects beyond a pipe elbow is difficult for axisymmetric wave impingement onto the elbow. For non-axisymmetric input to the elbow region, however, via partial loading around the circumference, allows natural focusing to occur because of angular profile variation around the circumference of the pipe. An experiment is reported here to demonstrate this process.

A Novel Technique With a Magnetostrictive Transducer for In Situ Length Monitoring of a Distant Specimen

A Magnetostrictive sensor was used to generate sound waves in a specimen through thirty feet of wire. Many hardware aspects are discussed such as boundaries, materials, acoustic horn design, and sound propagation characteristics which facilitated the generation of sound energy in the specimen. Temperature effects on velocity and length were calculated and a model was developed to determine length from a time of flight measurement. The specimen was heated in an oven to various temperatures and times of flight were measured and compared to the model. Results show agreement between the measured values and the model as well as the ability for a high precision length measurement.

Pressure Vessels Inspections Using Ultrasonic Phased Arrays

Phased arrays offer significant technical advantages for weld inspections over conventional ultrasonics. The phased array beams can be steered, scanned, swept and focused electronically. Beam steering permits the selected beam angles to be optimized ultrasonically by orienting them perpendicular to the predicted defects, especially Lack of Fusion. Electronic (linear) scanning permits very rapid coverage of the welds. Beam steering (usually called sectorial or azimuthal scanning) can be used for mapping welds at appropriate angles to optimize Probability of Detection of defects. Electronic focusing permits optimizing the beam shape and size at the expected defect location, also to optimize Probability of Detection. Overall, the use of phased arrays permits optimizing defect detection while minimizing inspection time. The paper describes the application of phased arrays for inspecting pressure vessel welds. Phased arrays offer significant practical advantages over conventional automated inspections. Thick section weld inspections typically use the established “top, side, end” or “top, side, TOFD” views of the weld. Other displays can be used, e.g. strip charts for zone discrimination scanning of narrow gap welds. Special inspections can be easily performed with phased arrays, e.g. additional beams for extra coverage, multiple angles or inspection set-ups simultaneously, or special scans such as tandem probes. Different delivery systems and instrumentation can be assembled for any required scan. Fitness-For-Service inspections requiring high PoD and accurate sizing can be performed using upscale systems. These phased array inspections can be tailored to any known code requirements.