Non-Destructive Testing Research Lines
Detection of loss of adhesion in fiberglass/epoxy composite pipes by non-destructive techniques
The use of composite materials in pipes for fluid transportation has become usual in the petroleum industry. PETROBRAS, for example, uses pipes with epoxy resin matrix reinforced with fiberglass, with diameters varying from 2” to 6” to transport oil at a temperature of 60ºC.
Connections between several sections of those pipes are made with Quick-lock and Taper-Taper Joints where the end of one of the pipes, which has certain conicity, is introduced in the next pipe, which also presents conicity though of a slightly bigger diameter. They are united with a specific polymeric adhesive for this type of joint and operational temperature. However, ungluing or loss of adhesion may bring line pressure drops, oil leakages or oil contamination making the assessment of the adhesive integrity and quality an urgent need.
This research line seeks to determine non-destructive test (NDT) methods capable of detecting a lack of adhesion and degradation with a time of the polymeric adhesive used in the joint of pipe sections with epoxy resin matrix with fiberglass reinforcement. It aims to assess the potential use of four NDT techniques (Ultrasound, Thermography, Acoustic Emission, and Radiography) to inspect and characterize failures on the mentioned materials, once there is no NDT technique consolidated to inspect composite materials and polymers nowadays.
All these tests will be complemented with information from typical corrosion tests such as cathodic displacement and tests in media where these materials are normally used.
Reliability studies using PoD (probability of detection)
PoD functions are widely used since the seventies to describe the reliability of a non-destructive test method or technique. This type of study ensures the structural integrity of critical components, avoiding health and environmental hazards.
A PoD curve is a mathematical curve similar to a probability cumulative function (varying between 0 and 1) that supplies information about the probability of the inspection technique to detect defects with sizes similar to a certain value. This is why a PoD curve may help to select the more suitable inspection technique. Using a reliability-based methodology a scientific approach for a rational inspection plan is possible. However, a limiting factor is the scarce literature data on PoDs of the different non-destructive inspection techniques. On the other hand, there are several factors that influence them such as inspection place, qualified personnel, automation degree, among others. Those facts evidence the need for more research in this area to effectively perform risk technique based inspections.
LNDC team intends to assess the reliability of non-destructive test techniques focusing inspection, initially for manual ultrasound technique and later expanding to other non-destructive techniques.
Reliability and study of corrosion defect inspection in oil storage tanks by acoustic emission method
Corrosion defects in the bottom of oil storage tanks are currently detected by acoustic emission (AE) non-destructive test, which allows the detection and localization of those regions at the bottom of storage tanks more impaired by corrosion.
However, the AE test procedure currently followed by PETROBRAS refineries does not consider the kind of corrosion defect detected in the test (localized or generalized), and neither relates the acoustic activity from the AE test with the loss of thickness of the plate.
The specific conditions needed for a corrosion defect to show detectable acoustic activity intensity are still obscure. This knowledge is concentrated on outsourcing companies that use specific criteria and programs to analyze results, and are unknown to the research and inspection team of PETROBRAS. In this scenario, this research performs a reliability study on the inspection of oil tank bottoms based on AE non-destructive tests and assess the specific conditions of the acoustic activity of corrosion defects in oil storage tank bottoms for this test.
Development of mechanical equipment/devices for submarine corrosion analyses in ship hulls by non-destructive test technique
This research seeks to develop two submarine vehicles, one for hull surface preparation for inspection and the other for ultrasound inspection. The preparation consists of a controlled hull cleaning operation removing the crust with suitable mechanical tools coupled to the vehicle. Inspection is performed with another vehicle, where immersion ultrasound transducers will be used to make hull thickness readings at different points, enabling the study of corrosion effects. Both vehicles will be able to work at 30 meters depth and will be remotely operated.
Development of new procedures for conventional and non-conventional techniques of non-destructive tests using computer simulation tools
Well-Succeeded radiography depends on numerous variables that affect the result and its quality. Many of those variables have a substantial effect on the results, while others have a minor influence. One of the difficulties found in applying radiography principles is the elapsed time between tests and analyses of the resultant radiography. It demands multiple tests (multiple expositions) to assess the effects of certain variables in the image quality.
This research aims to generate computational tools to help to obtain parameters capable of promoting high-quality radiographic images without a waste of time to adjust those parameters in the field. Research is based on the experimental results and is supported by computer simulation and database tools. One of the used tools is XRSIM software. One seeks the validation of the obtained results through software comparison with experimental results in order to be able to use it as a database to improve radiographic inspection.
Currently, radiography is the main non-destructive method used, but other techniques such as ultrasound and thermography will be explored as well.
Inspection and Characterization of duplex and super duplex stainless steels and welded Joints by non-destructive tests
The use of non-destructive inspection techniques in conventional stainless steel is well established. However, the non-destructive inspection of duplex and super duplex steels is a big challenge as those steels, being composed of ferrite and austenite, have some particularities. When using ultrasound, for instance, its waves propagate well in ferrite but suffer strong attenuation, scattering, and refraction in austenite.
In the case of magnetic and electromagnetic techniques, austenite presents a low electrical conductivity and a low magnetic permeability favoring inspection because of the detection of deeper defects and a better signal-to-noise ratio. On the other hand ferrite, because of its low electrical conductivity and high magnetic permeability, makes electric current penetration difficult and generates much noise due to its high magnetic permeability. Thus, the non-destructive inspection of those steels is still incipient, demanding further studies for better use.
Extended research is proposed on the inspection of duplex and super duplex steels, especially in welded joints, which presents the worst problems in those steels (incorrect ferrite/austenite balance and precipitation of deleterious phases). Ultrasound, Phased array, Rayleigh waves, TOFD, eddy currents, ACFM, ferrite content determination by ferrite scope and X-ray tests are expected to be performed. Samples of duplex steels heat-treated to obtain different deleterious phase contents, samples of those steels with known defects and, finally, real weld joints will be used in this study. All the analyses will be supported by a complete microstructural characterization of the samples to identify and quantify deleterious phases and the presence of other defects.
Grain orientation at the welded joints will be mapped by scanning electron microscopy with EBSD analysis to investigate its influence on ultrasound pulse response.