Showing papers by "Luis Volnei Sudati Sagrilo published in 2006"

MFL signals and artificial neural networks applied to detection and classification of pipe weld defects

Abstract: This work evaluates the use of artificial neural networks (ANNs) for pattern recognition of magnetic flux leakage (MFL) signals in weld joints of pipelines obtained by intelligent pig. Initially the ANNs were used to distinguish the pattern signals with non-defect (ND) and signals with defects (D) along of the weld bead. In the next step the ANNs were applied to classify signal patterns with three types of defects in the weld joint: external corrosion (EC), internal corrosion (IC) and lack of penetration (LP). The defects were intentionally inserted in the weld bead of a pipeline of API 5L-X65 steel with an outer diameter of 304.8 mm. In this way, the MFL signal itself, digitized with 1025 points, was used as the ANN input. Initially the signals were used as inputs for the neural network without any type of pre-processing, later four types of pre-processing were applied to the signals: Fourier analysis, Moving-average filter, Wavelet analysis and Savitzky–Golay filter. Signal processing techniques were employed to improve the performance of the neural networks in distinguishing between the defect classes. The results showed that it is possible to classify signals of classes D and ND using ANN with very efficient results (94.2%), as well as for corrosion (CO) and LP signals (92.5%). Also it is possible to classify the defect pattern signals: EC, IC and LP using neural networks with an average rate of success of 71.7% for the validation set.

Reliability of the manual and automatic ultrasonic technique in the detection of pipe weld defects

Abstract: The objective of this work is to evaluate the reliability of the ultrasonic non-destructive testing (NDT) technique, for specific test conditions, using PoD (probability of detection) curves developed by experimental procedures. Two classes of defects, lack of penetration (LP) and lack of fusion (LF), were intentionally inserted in 24 girth weld beads of an API X70 steel pipeline with an outer diameter of 254 mm and wall thickness of 19.05 mm. These welds were inspected using manual and automatic ultrasonic techniques. The automatic ultrasonic inspection was carried out using pulse-echo and TOFD (Time-of-Flight Diffraction) techniques and manual tests were carried out by five qualified inspectors using pulse-echo technique. The bootstrap technique was used in order to obtain a confidence interval for the PoD curves. The results, besides producing real PoD curves, showed the superiority of the automatic techniques over the manual test in the probability of detection of these two classes of defects.

A Reliability-Based Comparative Study for Mooring Lines Design Criteria

Abstract: The characteristic load effect for the design of mooring systems can be defined by means of three procedures: 1) an extreme sea state with a given return period, 2) a set of sea states on a contour line associated to a return period or 3) extreme response (tension) statistics for a long-term period. This work presents the result of a reliability-based partial safety factor calibration study for a LRFD mooring line design criteria considering the three approaches mentioned above. The calibration exercise is applied to three FPSOs considering North Sea environmental conditions and different water depths: 200m, 800m and 3000m. The mooring systems investigated take into account lines made up of chains and polyester ropes. It is shown that the design procedure based on the long-term response, among all water depths investigated, is the one that presents less scattered reliability indices around the target level.Copyright © 2006 by ASME

Reliability-Based Design Criterion for TLP Tendons

Abstract: This paper presents a Load and Resistance Factor Design (LRFD) criterion applied to the design of Tension Leg Platform (TLP) tendons in their intact condition. The design criterion considers the Ultimate Limit State (ULS) of any tendon section along its whole length taking into account both dynamic interactions of load effects and the statistics of its associated extreme response. The partial safety factors are calibrated through a long-term reliability-based methodology for the storm environmental conditions, like hurricanes and winter storms, in deep waters of the Campeche Bay, Mexico. In the reliability analysis, the uncertainties in the definition of load effects and analytic limit state models for calculation of tendon strength and randomness of material properties are included. The results show that the partial safety factors reflect both uncertainty content and the importance of the random variables in structural reliability analysis. When tendons are designed according to the developed LRFD criterion, a less scattered variation of reliability indexes is obtained for different tendon sections across a single or various TLP designs.Copyright © 2006 by ASME