Pipe Inspection Using Radiography and Software Simulation
Radiography and Software Simulation allow nondestructive ways to inspect pipes.
Corrosion is one of the greatest issues plaguing industries that rely heavily on piping distribution networks. If left unchecked, corrosion deteriorates the pipe's wall thickness (i.e., wall loss), which can lead to loss of structural integrity, product loss and in extreme cases, ruptures and explosions.
However, what makes pipeline corrosion particularly dangerous is that some defects are not readily visible. Unseen corrosion, such as those occurring inside the pipe or under insulation, can progress for months or years before they manifest as leaks or spills. (For a case study, see INFOGRAPHIC: The El Paso Natural Gas Company Pipeline Explosion.)
Preventive and corrective maintenance helps to protect the environment and the public by minimizing the risk of an industrial accident. This article discusses a study of pipe inspections that were performed using the nondestructive technique known as radiography.
The Benefits of Nondestructive Inspections
The benefits of nondestructive tests outweigh the benefits from contact tests, especially because nondestructive tests allow the pipe to remain in full continuous operation during the inspection.
One of the most important parameters of an inspection is a measurement of the pipeline's wall thickness. Only radiographic methods provide inspections without costly section removal or operational shutdown. In the case of insulated pipelines, the radiographic approach also provides the added convenience of allowing insulation material to remain in place during the inspection. An additional advantage is that this technique can be performed in high-temperature environments.
Radiography for Pipeline Inspections
Tangential film-based radiography is used to measure and monitor a pipe's wall thickness and the possible presence of corrosion. One study used a radiography station complete with its software simulation package and steel pipes as test specimens. During the examination of the pipeline, the steel pipes were placed sideways to show its crossing section. The radiography beam was then exerted and projected onto a film, thus taking a direct measurement of the wall thickness of the pipe. This is captured on the film and is measured and reviewed against an expected thickness. This tangential film radiography approach is implemented in several practical examples, such as experimental equipment of charge-coupled device camera and imaging plate.
Pipeline Inspections using Software Simulation and Discrete Tomography
A software simulation using discrete tomography can also be performed to reconstruct the pipe's cross section with its corrosion defects. Discrete tomography can be applied although there are only two known factors in the object to be reconstructed: the pipe specimen itself and air. Software simulation is a cost-effective approach for presenting the data measurements and projections. It can be optimized using a general optimization strategy of simulated annealing. An examination using the discrete tomography simulation can be further experimented with an effect of Gaussian noise.
Pipeline Inspections Using the Triune Mathematical Model (TUMM)
Another possible simulation approach uses the triune mathematical model (TUMM), which uses electromagnetic power. It is a theoretical basis of electromagnetic information-measuring systems. The specimen in the TUMM study is an underground insulated steel pipeline. The model is developed based on solutions of boundary-value problems of electrodynamics, the theory of electric circuits with distributed parameters, and the theory of the distribution of the field of currents of volume conductors. Natural soils are characterized as nonmagnetic and low conductor at a certain frequency. The magnetic field in the underground pipeline is a linear current distributor.
The basis of the triune mathematical model is the theory of electromagnetic fields of cylindrical structures. However, it may lead to cumbersome solutions with its complexity. Therefore, from the viewpoint of methodology, it is reasonable to consider simplified models (equivalent circuits and linear currents). For instance, characteristics of the spatial distribution of the magnetic field of currents is the basis for the selection of measured parameters (input values) and the construction of algorithms and systems of noncontact current measurements (NCM) and coordinates of underground pipeline.
The triune mathematical model allows one to investigate efficiently electromagnetic phenomena connected with the corrosion state of underground pipeline. It also simplifies the detection and analysis of informative features of an electromagnetic field and development of methods and systems for inspections of corrosion protection.
The electromagnetic field is described as a multilayer cylindrical structure with a local defect and two parallel insulated pipe walls by equations of hybrid waves. On the basis of the triune mathematical model, the interrelations between geometric and electric parameters of underground pipeline and characteristics of its electromagnetic field are investigated, and informative feature and ranges of measured values are determined. An analysis of a phenomenological electric circuit of a pipeline is performed, simplified equivalent circuits for special cases of direct current and alternating current are constructed.
Current measurements are performed in a non-contact pipeline inspection. Several methods of current measurements are gradient and parallax methods, cyclic method, and observation method with azimuthal and radial orientations. A recent technology of noncontact examination using integral, differential, and local inspections of corrosion protection of underground pipeline is developed using rational use of electrometry.
Fluoroscopy/Real-Time Radiography (RTR)
Fluoroscopy, or real-time radiography (RTR), works by converting invisible X-rays into visible forms of light. X-ray radiation is emitted on one side of the material, where it penetrates the object and is captured by sensors on the other side.
These sensors, which work by fluorescence, convert X-rays into light to produce real-time digital images. Fluoroscopy, which is faster and safer than traditional radiography, can be used to quickly reveal corrosion and other internal pipeline defects. Like computed radiography, this technology is also considered to be nondestructive, making it especially useful for detecting corrosion under insulation (CUI) without having to remove the lining
Detecting Corrosion with Digital Radiography
Nondestructive digital radiography techniques, like computed radiography and fluoroscopy, provide inspectors with a clear, safe and nondamaging assessment of the pipeline’s interior. Corrosion inspections with digital radiography involve the evaluation of shadow projections. Because the X-rays penetrate the pipeline, digital radiography has the ability to display pipe wall thicknesses. (Read also: A Look at Digital Radiography for Corrosion Inspection.)
Applications of Digital Radiography
The nondestructive nature of digital radiography makes it ideal for identifying defects in sensitive pipeline infrastructure such as those found in the oil and gas industry. The level of detail that can be obtained by this type of imaging technology allows it to be used for numerous inspection applications, including detecting and measuring the following:
- Uniform corrosion
- Erosion corrosion
- Corrosion under insulation (CUI)
- Flow-assisted corrosion
- Corrosion under pipe supports
- Welding corrosion
In addition to corrosion, digital radiography can also be a useful tool for identifying:
- Pipeline blockage
- Valve operational issues
- Liquid-vapor interfaces
In conclusion, the integration of the developed information technology (with developed hardware and methods) into the general system of CP is beneficial. It increases the efficiency and informativeness of inspections. It also enables one to pass from routine maintenance to more targeted maintenance or repair on the basis of the technical state for the prevention of damages. The technology also increases reliability and prolongation of the service life of critical, expensive and important underground pipelines and any other related structures.