Sergio Damasceno Soares

Relationship between acoustic emission and CTOD testing for a structural steel

Abstract 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.

Ultrasonic inspection of adhesive joints of composite pipelines

Composite pipelines are an attractive solution when traditional materials are not suitable for this purpose, which happens frequently at aggressive environments and also where the structural weight is a limiting factor. This work studies the application of the ultrasonic technique at the detection of defects as lack of adhesive and lack of adhesion, commonly found in adhesive joints of glass fiber reinforced plastic (GFRP) pipelines applied at onshore and offshore facilities. Computational simulations were conducted in CIVA 11© software (beta version) in order to obtain the best possible configuration for the inspections, applying the pulse-echo technique. Experimental results were compared to these simulations and several transducers were tested. An inspection methodology and reference blocks were developed for the calibration of the inspections. Some samples were selected for cutting in order to compare the ultrasonic results and the real condition of the joints. Results show that smaller frequencies ar...

An endoscopic shearography system with radial sensitivity for inner inspection of adhesion faults in composite material pipes

This work presents the development of a special shearography system with radial sensitivity and explores its applicability for detecting adhesion flaws on internal surfaces of joints of composite material pipes. The system uses two conical mirrors to achieve radial sensitivity. A primary 45° conical mirror is responsible for promoting the inspection of the internal surface all way around 360°. A special Michelson-like interferometer is formed replacing one of the plane mirrors by a conical mirror. The image reflected by this conical mirror is shifted away from the image center in a radial way and a radial shear is produced on the images. The concept was developed and tested. Two tubular steel specimens internally coated with composite materials and having known artificial defects were analyzed to test the ability of the system to detect the flaws. The system presented very good results on all inspected specimens. The experimental results obtained in this work are promising and open a new front for inspections of inner surfaces of composite pipes with shearography.

Evaluation of Non-destructive Techniques (Thermography, Ultrasound and Eddy Current) for Detection of Failures in Metallic Substrates with Composite Anticorrosive Coatings

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.

Uso de redes neurais artificiais na detecção de propagação de defeitos em dutos rígidos

The interest in monitoring equipment in real time is increasing in nowadays, mainly aiming the greater security of its operations. The Acoustic Emission (AE) testing has been the subject of developments with the aim of application in various types of equipment, especially in the inspection of rigid and flexible pipes. This paper presents the methodologies and results of a study of applying the method of Acoustic Emission to detect propagation in defects in pressurized rigid pipes, being a pioneering work in this area of research. In this way, specimens were manufactured with defects artificially inserted. These specimens were submitted to hydrostatic testing and the defect propagation was monitor by AE. The ultrasound by Time of Flight Diffraction (TOFD) was the technique chosen to monitor the defect growth. The AE resulting signals were divided into the classes No Propagation (SP), Stable Propagation (PE) and Unstable Propagation (PI) and used as inputs set in the implementation of nonlinear classifiers by error back propagation. The correct classification results reached close to 86%, proving the efficiency of the method for the conditions tested in this job.

Detection of the Propagation of Defects in Pressurized Pipes Through the Acoustic Emission Technique Using Artificial Neural Networks

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

PETROBRAS Criteria for Acoustic Emission and Fracture Mechanics Relationship

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