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The aim of this work is to make a survey of typical flaws presented by modern anticorrosive coatings commonly employed for inside protection of petrochemicals storage tanks and discuss what can be expected from nondestructive inspection with conventional eddy current technique. In this sense, advantages and limitations of the method are discussed taking into account the characteristics of the coatings. Controlled defects were machined in carbon steel substrates in order to simulate localized corrosion. The detectability of the eddy current technique was evaluated for as-applied insulating coatings (with different thicknesses) in presence and absence of iron oxide inside the simulated corrosion defects. Comparing the results obtained with the original C-Scan maps and after the image processing, the machined defects were successfully detected. In this comparison, it was observed a significant improvement for the false defects elimination using image processing. Keywords: Eddy current testing, Coatings, Corrosion, Underfilm corrosion, Pitting

The aim of this study is to evaluate the ability of three nondestructive techniques—ultrasound, thermography and eddy current—for the detection of defects that can occur in metallic substrate with anticorrosive coating and compare the results regarding the advantages and disadvantages of each one of these inspection techniques. For this study, samples were made from a metallic substrate in which a composite anticorrosive coating and two types of defects were introduced: localized corrosion (defects of different geometries and depths inserted into the metallic substrate) and adhesion failure between the coating and the substrate. According to the results, all three techniques showed to be able to detect defects simulating localized corrosion on the substrate. However, the adhesion failure was only effectively detected by thermography and ultrasound and a high correlation between these two techniques was observed.

Acoustic emission testing may be employed as a nondestructive technique to detect flaws in materials and equipment. For pressure vessel construction, the test requires loading by internal pressure in order to open the flaw tips and to generate acoustic emission signals. The present work tries to investigate whether the required pressure level causes flaw propagation, risking vessel integrity. The material employed was a fine grained normalized C-Mn structural steel (ASTM A 516 gr. 60). Fracture mechanics crack tip opening displacement (CTOD) tests were conducted and the acoustic emission probes were placed on the testpieces, which enabled a correlation to be established at any moment between the crack acoustic behaviour and its CTOD value. A relevant result was that intense acoustic activity was detected before the first stable crack extension occurs. On a quantitative basis, it was found that the CTOD value corresponding to the first detectable acoustic emission from the loaded crack tip is lower than the CTOD for the initiation of stable crack propagation. As a final conclusion from this work, it can be said that for this specific steel, acoustic emission testing may be reliably performed at sufficiently low CTOD values, where the risk of fracture may be discarded.

Abstract Deep water oil and gas exploitation in Brazil has considerably increased the utilization of flexible pipes in conjunction with floating production systems. Acoustic emission is a nondestructive testing technique that could be used for detection of tensile armour wire rupture, which is a critical failure mode of flexible risers. This paper describes the experimental program implemented including: laboratory results, field experience and the model to define if there is or no armour wire rupture. It was concluded that acoustic emission can be used as a tool to help the integrity assessment of flexible risers using the setup and model developed during this experimental program. Introduction Deep water oil and gas exploitation in Brazil has considerably increased the utilization of flexible pipes in conjunction with floating production systems. Periodic inspections have detected considerable occurrence of damage on the top section of flexible risers which may affect their structural integrity. In order to mitigate the progression of these damages monitoring techniques have been studied and implemented for a continuous flexible riser integrity assessment, apart from the inspection program. Acoustic emission is one of these techniques for detection of tensile armour wire rupture. This paper describes experimental program implemented including: laboratory results, field experience, equation to define if there is an armour wire rupture or not. It was concluded that acoustic emission could be used as a tool to help the integrity assessment of flexible risers. Acoustic emission is a physical phenomenon occurring within materials. The term acoustic emission is used to define the elastic energy released within a material in the form of transient elastic waves. The application of load and/or the presence of a harsh environment produce internal modifications such as crack growth, local plastic deformation and corrosion, and in some cases phase changes. Thus it provides some information about the internal behavior of the materials under consideration. The waves are detected by means of suitable sensors which make it possible to convert the surface movements of the material into an electric signal. These signals are processed by appropriate instrumentation with a view to indicating and locating the acoustic emission sources. Figure 1 shows the schematic principle of the acoustic emission testing. [AFIAP, 2004]

The acoustic emission test has distinguished relevance in non-destructive testing and, therefore, existing research abound at present aiming at the improvement of the reliability of their results. In this work, the methodologies and the results obtained in a study performed are presented to implement pattern classifiers by using artificial neural networks, aiming at the propagation of existing defects in pressurized pipes by means of Acoustic Emission testing (AE). Parameters that are characteristic of AE signals were used as input data for the classifiers. Several tests were performed and the classification performances were in the range of 92% for most of the instances analyzed. Studies of parameter relevance were also performed and showed that only a few of the parameters are actually important for the separation of classes of signals corresponding to No Propagation (NP) of defects and Propagation (P) of defects. The results obtained are pioneering in this type of research and encouraged the present publication.Copyright © 2006 by ASME

During the last years, PETROBRAS has used acoustic emission technique as an inspection tool. In this period, the acoustic emission concept has changed from a revolutionary technique to a global inspection technique with the aim of indicating areas to complementary inspection. In the last years more than 600 acoustic emission tests were done in equipments like pressure vessels, reactors, tanks, spheres, and etc. In 2002, the results of acoustic emission tests and nondestructive tests done on these equipment were collected to build a database in the PETROBRAS environment. Analysis made in this database has shown that exists a clear relationship between acoustic emission and the severity of flaws.Copyright © 2006 by ASME