Thickness change

Projection radiography is widely used for pipe inspection and corrosion monitoring. Film digitisation allows a direct access to the local density variations by computer software. Following to a calibration step an interactive estimation of local wall thickness change based on the obtained density variation is possible. The theoretical model is discussed, the limitations of the application range are shown and examples of the practical use are given. The accuracy of this method is compared to results from wall thickness measurements with ultrasonic devices. 

Basically it is only possible to determine a wall thickness change in penetration direction from a density variation of a radiographic film. No absolute wall thickness values can be obtained in this way contrary to the tangential method. 

After this calibration step (the effective absorption coefficient is determined from a known wall thickness change and the corresponding variation of the optical film density) the evaluation of local wall thickness changes Aw (corresponding to De,o) from the nominal wall thickness w o , (corresponding to Dnom) can be done according to ... 

Note that this relationship is in conPadiction to the well known equation for the calculation of the thickness resolving power given by Halmshaw in 111. The relationship in 111 requires explicit knowledge about built-up factors for scatter correction and the film contrast factory (depending on D) and is only valid for very small wall thickness changes compared to the nominal wall thickness. 

But there are many practical applications where no known wall thickness change can be obtained from the radiographic film under consideration because at the exposure it was not... 

The second influence must be separated clearly from the first to achieve reliable results. This can be done in the most practical cases using symmetry axes of the object, where the geometrical influence is small eompared to the real wall thickness change. 

Profile Plot This window display the data (grey values, optical densities or wall thickness changes in mm after calibration) along the line shown in the image window. 

In fig, 4 local corrosion by erosion is shown in a pipe with a bore of 100 mm behind a welding. In this case only the nominal wall thickness of the pipe is known (6.3 mm). To calibrate the obtained density changes into wall thickness changes a step wedge exposure with a nominal wall thickness of 13 mm (double wall penetration in the pipe exposure) and the same source / film system combination was used. From this a pcff = 1-30 1/cm can be expected which is used for the wall thickness estimation of the pipe image according to equation (4). 

Holographic information can be recorded by spatially modulating either (or a combination of) the absorption or phase (index or thickness change). 

Software packages are commercially available for simulation of hydrauhc transients. These may be used to analyze piping systems to reveal unsatisfactoi y behavior, and they aUow the assessment of design changes such as increases in pipe-wall thickness, changes in valve actuation, and addition of check valves, surge tanks, and pulsation dampeners. 

Next, the straight-sided tension specimen has a transition region that is created by thickness change (instead of the width change of the ASTM D 638 specimen) as shown in Figure 2-22. Failures typically occur either in the bonded tabs or in the gage section. If the bonded tabs fail, then the failure load is never a measure of the subject material s strength ... 

Equation (7) indicates that the critical film thickness changes very slowly with an increase in initial viscosity when it is close to 26 nm. 

Twenty scans wepe co-added to produce one spectrum at a resolution of 4 cm every 30 seconds. The reaction was followed by monitoring the absorbance of isocyanate as a function of time. Film thickness changes were compensated for by normalizing the isocyanate absorbance to the 1446 cm band which remains constant in absorbance during the reaction. The infrared absorbance of the free isocyanate is converted to concentration by comparison to the absorbance observed in a similar sample which has no functional groups with which the isocyanate can react. 

The same observations are true for the evanescent wave of the modes in the surrounding medium. Moreover, these changes in the field distributions are accompanied by an increase of the effective refractive indices of the cladding modes, as will be clarified later. For this reason and by virtue of (3.1), the resonance wavelengths of the coated LPG are expected to blue-shift in response to an overlay thickness change. 

The developed sensor was used for ultrathin-film measurement. The reflection spectrum was shifted during the deposition of thin films (e.g., self-assembly of polyelectrolyte layers) onto the sensor end. The reflection between the thin film and the fiber endface was neglected because of their similar refractive indices. As the film increased its thickness, the length of the fiber cavity changed. The amount of change was estimated by the phase shift of the interferogram. The device could also be used as an immunosensor in which the optical thickness changes were used to... 

Fig. 8.41 Simulated resonance curve shift with the thickness change of the lipid membrane...

Fig. 9.6 The calculated effective index change in the silicon PWEF waveguide of Fig. 9.3 induced by adsorbed films of constant optical thickness (a) Dopt 0.4 nm and (b) Dopt 0.1 nm for film thickness between 0.5 and 16 nm. As the film thickness changes, the refractive index is adjusted so that the optical thickness remains constant. For comparison, the graphs also show 8iVeff and the corresponding SPR angle shift A6 for an SPR experiment...

Blue Grass liner change-outs—all titanium and C-276 liners 0.5-in. initial wall thickness, change-out when 0.2 in. remaining. 

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