Carsten Bellon

X-ray modeling for industrial applications

A computer package for the simulation of the X-ray imaging process in nondestructive evaluation (NDE) is presented. The components of the radiographic inspection system are considered independently, i.e. the characteristics of the source, the geometry and the material properties of objects and defects, as well as the imaging process itself. The model is based on a ray tracer technique describing the attenuation of the radiation. The scattering effect is included in terms of built-up factors. A CAD-interface provides the opportunity to arrange independent CAD objects, e.g. the component geometry or defect shapes, defining a testing scheme. Complicated defect shapes are created by a preprocessor, the built-up factors can be received from experiments or from a separate model using an efficient solution of the scattering problem based on the theory of Markovian processes with random structure.

Computer Simulation of X-Ray NDE Process Coupled with CAD Interface

Tools for computer simulation are helpful in NDE manyfold. A global conception of reliability in NDE can include among other procedures performance prediction by computer simulation. POD data of simulated defects can be calculated. Computer simulation gives the possibilities to optimize testing parameters, to make feasibility analysis for special testing problems, and to support the interpretation of testing results especially in case of complex component geometry. In this way simulation tools are valuable for planning and for evaluating of the examinations.

Computer Simulation of Radiographic Process — A Study of Complex Component and Defect Geometry

In proof of the applicability of a testing method, a global concept of reliability of NDE should be used which is based on both the theoretical and experimental procedure demonstration. This concept includes consequently the performance demonstration of the whole testing chain, including the physical method, the device and the inspector, by using statistical methods as well as empirical data base, and the performance prediction by computer simulation. In addition to this, the computer modeling can be used to optimise testing parameters, to make feasibility analysis for special testing problems, and to support the interpretation of indications, especially for very complicated component geometry. Thus, this variety of applications makes it necessary to develop an easy and practical model to describe the process of radiographie testing with good accuracy and with a small numerical expense, which may include any component geometry and uses experimental findings. A macroscopic model for the X-ray projection process was developed where the X-ray beam and target interaction is described as a simplified transport process. The influence of the scattering effects on the imaging process can be realised with acceptable accuracy by using a global description. The efficiency and limits of the model are discussed in terms of different examples exploring the detectability of cracks with complicated geometry. These cracks are considered for different types of high performance materials: (i) composites in the aircraft and space industry sector and (ii) realistic austenitic welding from the nuclear industry sector. These examples will show the capability of the modeling tool to handle also complicated object geometries and testing conditions like double wall penetration and ellipsoid shot.

Simulation of Scattering Process in Radiation Techniques Exploiting the Theory of Markovian Processes with Random Structure

There are a lot of physical and technical problems that need to calculate photon density distribution functions for the photon flow passing materials of different type. This flow can be described by a type of transport equations similar to the Boltzmann equation. Notwithstanding the huge number of equation types depending upon the particularities of the photon-matter interactions, the main properties of their trajectories are similar. Therefore it is possible to find a generalized model description for the photon trajectories which can be used to solve a large number of other problems.

SIMULATION AND EXPERIMENTAL VERIFICATION OF X-RAY SPECTRA

A model is discussed which describes the generation of X‐rays in conventional tubes using tabulated Bremsstrahlung energy spectra depending on three variables: the target atomic number, the incident electron kinetic energy, and the fraction of energy radiated. The constructed model includes technical tube parameters like kilovoltage, target material and target angle to also account for self‐absorption in the target, as well as radiographic parameters like filtering. Additionally a parameter‐free description of the characteristic radiation is included in the model. With the help of the simulation tool the influence of parameters can be separately studied. The validity of the proposed model is shown by measurements. This research is supported by the German Federal Ministry of Economics and Technology under contract MNPQ transfer II D 5‐30/06.

Measurement and modeling of scatter ratios at high energies

Determining scatter ratios at high energies (>∼1 MeV) presents challenges not immediately obvious from measurements at conventional X‐ray energies. This includes reduced attenuation even in heavy elements as well as a stronger forward bias of scattering. In order to check the reliability of different measurement setups with regard to material thicknesses, distances, and collimation, attenuation and scattering were separately simulated using a Monte Carlo model. The simulation results help in understanding the sources of radiation scattered into the detection area, thereby aiding in eliminating undesired contributions.

Modelling based radiography for NDE of subsea pipelines

This work presents the use of limited experimental measurements to develop a set of calibrated simulation parameters that can then be used for reliable simulation of subsea pipeline inspections. The modelling software aRTist is used as the simulation tool, and the calibration is through comparison with experimental images of a well characterised sample in a water tank. Image quality parameters such as signal-to-noise ratio, contrast and basic spatial resolution are compared with the aim of matching simulated values to experimental results. Currently the model is partially calibrated, with signal-to-noise ratio successfully matched while differences are still found in contrast-to-noise ratio comparisons. This means that measurements depending on absolute intensity are not accurate enough in the simulation at this stage. However, the simulation is found to be accurate for wall thickness measurements in tangential images, which are not based on absolute intensity, with simulated and experimental cases produc...

Monte Carlo Simulation Tool with CAD Interface

In radiography, irradiating the object and recording the transmitted radiation gives information about the inner structure of an object. The transmitted radiation consists of a primary and a scattered component. The Monte Carlo method allows the detailed description of the physics of radiation transport. On the other hand, it is necessary to handle complex object geometries to be able to simulate realistic inspection scenarios. Standard Monte Carlo programs like the Monte Carlo n‐particle transport code MCNP (Los Alamos National Laboratories) use mainly simple geometrical forms such as parallelepipeds, ellipsoids, or planes to construct complex geometries in a proprietary way. Here a model is presented that combines the Monte Carlo method with the world of CAD. Components are described as closed triangulated surfaces using STL as exchange format, which is supported by all CAD systems. The opportunities of the presented Monte Carlo simulation tool are discussed in terms of various examples and compared to MCNP.In radiography, irradiating the object and recording the transmitted radiation gives information about the inner structure of an object. The transmitted radiation consists of a primary and a scattered component. The Monte Carlo method allows the detailed description of the physics of radiation transport. On the other hand, it is necessary to handle complex object geometries to be able to simulate realistic inspection scenarios. Standard Monte Carlo programs like the Monte Carlo n‐particle transport code MCNP (Los Alamos National Laboratories) use mainly simple geometrical forms such as parallelepipeds, ellipsoids, or planes to construct complex geometries in a proprietary way. Here a model is presented that combines the Monte Carlo method with the world of CAD. Components are described as closed triangulated surfaces using STL as exchange format, which is supported by all CAD systems. The opportunities of the presented Monte Carlo simulation tool are discussed in terms of various examples and compared to ...

Corrosion Monitoring with Tangential Radiography and Limited View Computed Tomography

Accurate and reliable detection of subsea pipeline corrosion is required in order to verify the integrity of the pipeline. A laboratory trial was conducted with a representative pipe sample. The accurate measurement of the wall thickness and corrosion was performed with high energy X-rays and a digital detector array. A 7.5 MV betatron was used to penetrate a stepped pipe and a welded test pipe of 3 m length and 327 mm outer diameter, with different artificial corrosion areas in the 24 mm thick steel wall. The radiographs were taken with a 40 x 40 cm² digital detector array, which was not large enough to cover the complete pipe diameter after magnification. A C-arm based geometry was tested to evaluate the potential for automated inspection in field. The primary goal was the accurate measurement of wall thickness conforming to the standard. The same geometry was used to explore the ability of a C-arm based scanner in asymmetric mode for computed tomography (CT) measurement, taking projections covering only two thirds of the pipe diameter. The technique was optimized with the modelling software aRTist. A full volume of the pipe was reconstructed and the CT data set was used for reverse engineering, providing a CAD file for further aRTist simulations to explore the technique for subsea inspections.

Reliability Assessment by Simulation for High Energy Radiography

Efficient and reliable nondestructive evaluation techniques are necessary to ensure the safe operation of complex parts and construction in an industrial environment. Radiography is one of the classical nondestructive testing techniques widely applied in industry. Over the years modeling became more and more important in modern NDE. It is increasingly used to optimize techniques for complex applications and to support the preparation of written procedures. Hence, computer modeling has to be able to handle all significant properties of a NDE system with sufficient accuracy. In case of radiographic applications the model includes the radiation source, the interaction of radiation with material, the detection process, and the geometrical description of the part or the construction. As known from practice the last can be very complex and requires a description that allows the handling of arbitrary geometries. The link between NDE models and CAD provides the ability to quantitatively evaluate complex inspectio...