Film Density Measurements Research Articles

Tangential X-Ray Radiography for Pitting Geometry Analysis of Outside Wall of Insulated Steel Pipes

The piping systems used for the transportation of liquids and gases in power stations, petroleum petrochemical facilities, and chemical plants are significantly impacted by corrosive processes. One of the most destructive forms of corrosion is pitting corrosion, which produces holes on piping metal surfaces. Monitoring pit depth is necessary in order to prevent leakage in the piping system, especially during operation. However, measuring pit depth as a part of periodical inspections is complicated since the pit depth on the outside wall of a pipe may vary. Non-destructive testing (NDT) methods such as ultrasonic, liquid penetrants, and magnetic particles are used to detect defects in industrial components; however, they first require the removal of insulation and the shutdown of the pipe system. Another alternative NDT technique, tangential radiography technique (TRT), offers a solution to this problem as tests can be conducted without removing piping insulation, allowing testing while the piping system is online. In this study, we tested TRT using an X-ray radiation source, which has good controllability (i.e., intensity and exposure time) and a lower impact on the human body than do γ-ray sources. We focused on the comparison of film density measurements using a density meter and a light meter. The magnification of pit diameter was used to obtain an equation for small-diameter pipes (i.e., diameter of less than 50 mm). The working voltage was varied (200, 230, and 260 kV) in order to generate appropriate X-ray energies to measure various pit depth (20, 40, and 60%, receptively) of a stepped steel pipe specimen. Film density measurements using the density and light meters showed similar results; however, the film density result using the density meter was more accurate. All tangential side edges of the specimen burned off for film densities above 3.5. Degrees of magnification (1.0123, 1.0254, and 1.0379) varied as a function of distance from the midpoint of the X-ray target (30, 60, or 90 mm, respectively). Using the results, a linear equation with three variables was obtained to determine the actual diameter of pitting: 0.000385436a + 0.038350128b + 0.000467083c = d; where the actual diameter = film diameter/d. High working voltage produced low film contrast, high film definition, and low scatter. Low working voltage produced high film contrast, low film definition, and high scatter. Based on our results, a working voltage of 260 kV is most appropriate for effective analysis.

Dependence of surface free energy on molecular orientation in polymer films

Surface free energy of mechanically drawn polycarbonate films was determined using contact angle measurements and shown to increase with orientation. The increase in polymer film surface free energy was attributed to increased polymer chain packing during orientation, supported by film density measurements, which provides enhanced intermolecular interactions. Surface free energy can therefore be increased by, or used to predict, polymer orientation.

Spontaneous molecular orientation of polyimides induced by thermal imidization (6). Mechanism of negative in-plane CTE generation in non-stretched polyimide films

The mechanism of negative coefficient of thermal expansion (CTE) generation for non-stretched polyimide (PI) films is proposed in this work. Negative CTE behavior was observed in some miscible binary blend films composed of a major fraction of a rod-like semi-crystalline PI derived from pyromellitic dianhydride (PMDA) with p-phenylenediamine (PDA) and flexible PIs based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) whereas homo PMDA/PDA PI film shows a considerably low but a positive CTE value. The results suggest that the negative CTE generation is related to not only a considerably high extent of in-plane orientation of the PMDA/PDA chains but also to the crystallinity of the blends. The present work revealed that some other PIs, a poly(ester imide), and a polybenzoxazole system also display negative CTE and these systems also possess extremely high extents of in-plane chain orientation without exception. In addition to CTE, the morphologies were monitored as a function of imidization temperature for two PI systems, PMDA/2,2′-bis(trifluoromethyl)benzidine and PMDA/m-tolidine by wide-angle X-ray diffraction, FT-IR spectroscopy, birefringence, and film density measurements. The results suggested that the negative CTE phenomenon occurs when PI films possess very high extents of in-plane orientation and a less crystalline morphology simultaneously, thereby significant thermal expansion can be allowed to the thickness direction.

Acoustic resonant spectroscopy for characterization of thin polymer films

An acoustic resonant spectroscopy technique for measuring the acoustic impedance, ultrasonic velocity, and density of micron-scale polymer films is developed. The method, which is based on spectral analysis, observes the acoustic resonance between water, the film, and a tungsten plate with high acoustic impedance in the frequency range of 20–70MHz. The interface between the film being examined and the plate is vacuum sealed, enabling us to characterize the low-density polyethylene film with acoustic impedances as low as about 1.9MNm−3s and the poly(vinyl chloride) film as thin as about 8μm. The error in the film density measurements is found to be less than 1%, and the validity of the technique is verified.

A radiographic calibration method for eddy current testing of heat exchanger tubes

The most technically available NDT method for in-service inspection of heat exchanger tubes is eddy current testing. Using a differential ID bobbin probe, tubes can be tested with high speed, but for accurate estimation of tube condition, precisely machined calibration blocks from the same material are necessary. The purpose of this work was to calibrate the eddy current system by radiography without the use of expensive calibration blocks. Wall thickness measurement and deterioration determination due to corrosion/erosion/pitting was evaluated in this study by using radiograph ie film density measurements. It was found that this method can determine the remaining wall thickness as well as pitting corrosion in the tubes using differential and absolute film density measurements. Results show that good precision can be obtained with this method of eddy current system calibration.

In-service corrosion evaluation in pipelines using gamma radiography – a numerical approach

Wall thickness measurement and deterioration determination of 6 and 10 inch pipes due to corrosion/erosion/pitting was evaluated by using radiographic film density measurements. Special reference blocks were prepared withdefined step wall reductions and artificial defects. Gamma radiography with a Ir-192 source was used. A double-wall technique with longitudinal film arrangement was used for this purpose. Formulae were developed from the experiments for numerical calculations. It was observed that this method can determine remaining wall thickness as well as pitting corrosion in insulated and non-insulated pipes with differential and absolute density measurements. The purpose of the work was the optimisation of techniques, quality control, evaluation of radiographs and parameters affecting the results. Furthermore, the studies included investigation on the limitations of each technique and stability of test conditions. Results show good precision - above 97% - between real and calculated values.

COMPARISON OF SINGLE‐PHASE AND HIGH‐FREQUENCY GENERATORS FOR X‐RAY UNITS

The purpose of this study was to compare characteristics and performances between single-phase (SP) and high-frequency (HF) generators for x-ray units dedicated to veterinary radiology practice. A 30-kW SP and a 30-kW high HF generator connected to a rotating anode x-ray tube were used for the study. Source-film distance, screen/film combination, and film processing were kept the same during the experiment. The mAs value yielding a similar film optical density of a stair step phantom, as assessed by a densitometer and a similar dose, as assessed by a solid state detector, was estimated for different kVp values. The ratio of the mAs used with the SP generator to the equivalent mAs used with the HF generator to produce similar film density or radiation dose was calculated. Subject contrast was measured for different kVp values as the relative difference in film optical density between two steps of the phantom. The waveform of the tube current was recorded for the two generators using an oscilloscope. Motion artifact was produced on a lateral radiograph of a canine tarsus using the two generators. Reproducibility was assessed by comparing the variances of film density measurements made on the central step of the phantom on 10 consecutive images produced with the two generators. mAs ratios (SP/HF) to obtain similar film optical density ranged from 2 (for 90kVp) to 2.5 (for 70 kVp), and mAs ratios to obtain similar radiation dose ranged from 1.2 (for 100 kVp) to 1.4 (for 70 kVp). Image contrast was slightly higher for the SP than for the HF generator. Current waveform for the SP generator was half-sinusoidal and it was almost continuous for the HF generator. Motion artifact appeared as blur for the HF generator and as several regularly placed images of the subject for the SP generator. Reproducibility was significantly better for the HF than for the SP generator (P = 0.047). It was concluded that the HF generator was approximately two times more efficient, had a better reproducibility, and produced images with a lower contrast than the SP generator. Motion artifact appears differently due to different current waveform.

Preparation and characterization of SiO2–B2O3–P2O5 particles and films generated by flame hydrolysis deposition for planar light-wave circuits

Boron-phosphosilicate glass particles were deposited on Si wafer by flame hydrolysis deposition under controlled conditions. A few ten nanometer sized and spherical glass particles were synthesized in an oxy-hydrogen flame. The wafer surface temperature of 500 °C proved sufficient to form the Si–O–B framework while a higher temperature (approximately 730 °C) was required to produce Si–O–P formation. Gaussian bands at 3242 cm−1 provided evidence that the dissolved B2O3 concentration increased with the substrate temperature. In as-deposited porous films, a certain quantity of crystalline B2O3 remained, which was completely transformed into the noncrystalline phase after post deposition annealings. Film density measurements indicated that the B2O3 content in the doped silica films would be substantially lower than that in the precursor mixture.

Quantitative use of film density variations for thickness variation determination by polychromatic X-radiography

Abstract Based upon calculation of the attenuation of poly-energetic x-rays through a sample of known composition, derivation of the film contrast factor and estimation of the build-up factor, film densities may be applied for quantitative determination of the inspected sample thickness variation, without the need of imaging a calibration sample during the exposure. The accuracy and reliability of such calculations has been tested using the radiographs of an aluminium step wedge with known thickness variations. This allow calculation of the variation of the build-up factor with aluminium step wedge thickness for relatively small total sample thicknesses and at low x-ray energies. Different exposure at varying exposure time and on different x-ray films were performed in order to assess the film contrast factor and to evaluate the variability of the results on the build-up factor variation with sample thickness. The trend of the build-up factors as a function of sample thickness for different peak x-ray energies shows a minimum at approximately 9–11 mm sample thickness, slowly increasing values for smaller sample thickness values, and rapidly increasing values for larger sample thicknesses. The explanation for the observed minimum is somewhat uncertain, although it can be concluded that the calculation procedure for the linear attenuation coefficient results in a compensation for the beam hardening effect. The calculation procedure for determination of sample thickness variations based on film density measurements is examplified using the results of the build-up factor determination. A 2.0 mm aluminium step thickness difference was derived from film density measurements at an accuracy better than 90%. The accuracy of the results depends mainly on the accuracy of the fit of the film contrast factor as a function of film density and the accuracy of the build-up factor values as a function of the sample thickness.

Quantitative Use of Film Density Variations for Thickness Variation Determination by Polychromatic X-Radiography

Abstract Based upon calculation of the attenuation of poly-energetic x-rays through a sample of known composition, derivation of the film contrast factor and estimation of the build-up factor, film densities may be applied for quantitative determination of the inspected sample thickness variation, without the need of imaging a calibration sample during the exposure. The accuracy and reliability of such calculations has been tested using the radiographs of an aluminium step wedge with known thickness variations. This allow calculation of the variation of the build-up factor with aluminium step wedge thickness for relatively small total sample thicknesses and at low x-ray energies. Different exposure at varying exposure time and on different x-ray films were performed in order to assess the film contrast factor and to evaluate the variability of the results on the build-up factor variation with sample thickness. The trend of the build-up factors as a function of sample thickness for different peak x-ray energies shows a minimum at approximately 9–11 mm sample thickness, slowly increasing values for smaller sample thickness values, and rapidly increasing values for larger sample thicknesses. The explanation for the observed minimum is somewhat uncertain, although it can be concluded that the calculation procedure for the linear attenuation coefficient results in a compensation for the beam hardening effect. The calculation procedure for determination of sample thickness variations based on film density measurements is examplified using the results of the build-up factor determination. A 2.0 mm aluminium step thickness difference was derived from film density measurements at an accuracy better than 90%. The accuracy of the results depends mainly on the accuracy of the fit of the film contrast factor as a function of film density and the accuracy of the build-up factor values as a function of the sample thickness.

Film dosimetry analyses on the effect of gold shielding for Iodine‐125 eye plaque therapy for choroidal melanoma

One of the methods currently being used to treat choroidal melanoma employs an episcleral plaque containing I-125 radioactive seeds. However, comprehensive dosimetry studies on the plaque are scarce and controversial. For this work, we use film to study the dosimetry outside the lip of the gold shield of the eye plaque. This lip around the gold shield was made to protect the critical structures behind and adjacent to the lesion. Since the changes of energy spectrum of I-125 in tissue are negligible, film dosimetry seems to be a logical choice because of high spatial resolution required around the lip of the gold plaque. For this study, we first established an H and D curve with dose expressed in a unit of specific dose rate constant. This avoids absolute dose measurements. All film density measurements are made with a 1-mm aperture scan, normalized to the density at the prescription point for tumor of 3-5-mm apical height, i.e., 5 mm from the interior surface of sclera, and converted to percentage isodose curves. With a gold shield, it is found that when the plaque is placed against the optical nerve, the optical disk and macula, located at 2 mm outside the lip, on the exterior surface of sclera, may receive 85% of the prescription dose for a 12-mm plaque and 58% for a 16-mm plaque. For tumors of 8-mm apical height, the optical nerve would receive more than the prescription dose.

Radiometric procedure for linearising computer-interfaced display systems

Procedures for the adjustment of computer-interfaced display devices have been based on a subjective approach, generally relying on the visual examination of digital test patterns. The lack of an objective adjustment procedure means that the best image quality may not always be achieved. The authors describe how a simple home-made radiometer can be used to make screen luminance as well as density measurements on transparency film. The measurements are first used to determine the brightness and contrast settings for the display which enable the film to be used in the linear range of its optical densities. The display device characteristics, showing how luminance varies with grey level, are then determined. Using this information a simple display-linearising mapping can be produced to ensure that screen luminance (and hence film density) is a linear function of display grey-level value. Film-density measurements are also used to investigate the luminance and hence phosphor uniformity characteristics of the screen.

Photography as a technique for studying visual range

A technique is described that uses black and white and color photography to study visual range, and the effects of clouds and haze on a scene. Black and white film is used for quantitative measurement of visual range. Film density measurements are digitized using a flying spot scanner to assure that the measurement, analysis and interpretation are reproducible and accurate. The density wedges and the negatives are digitized. The procedure and an example are presented. Color film is used to qualify the black and white measurements. The techniques applied in analysis and some results of the field measurement program are presented.

Optical and physical properties of vacuum-deposited PbS films

We describe the film density, void volume, thickness, species, reflectivity and crystal size of vacuum-deposited PbS films. Film densities, as determined from film thickness and areal film density measurements, were approximately one-half that of bulk PbS, resulting in a calculated average film void volume of about 60%. Film thicknesses ranging from 160 to 890 nm measured with the stylus and interferometer measuring methods were accurately determined for PbS films overlaid with approximately 100 nm of aluminum. The ion backscattering measuring method yielded an average [S]/[Pb] ratio of 0.955±0.07 or 1.00 (within experimental errors). The specular reflectivity of the glass-film interface of prism substrates, measured at an angle of incidence of 45° and at λ = 1060 nm, decreased as deposition time increased. The PbS films exhibited two sizes of crystals with the smaller located near the glass-film interface. The stylus, interferometer and ion backscattering measuring methods are useful in determining the density, void volume, thickness and species of vacuum-deposited films.

Crop surveys from multiband satellite photography using digital techniques

Multiband and Multibase photography of the Imperial Valley, California, taken during the Apollo 9 mission was analyzed using statistical multispectral pattern recognition techniques. With a scanning microdensitometer, 70-mm frames were converted into digital form and stored on magnetic tape. All analysis was conducted using a digital computer which enabled rapid automatic processing of any of over five million film density measurements. Automatic recognition of fields of barley, sugar beets, and alfalfa was attempted, and the recognition accuracies were 75% for barley, 59% for sugar beets, and 27% for alfalfa. Highly accurate detection of bare soil, salt flats, and water was achieved. Low percentage ground cover crops such as lettuce, onions, carrots, and cabbage were indistinguishable from bare soil. Results using multiband photography are compared with results using color separations of color infrared photography which covered approximately the same bands.