Sergio Ricardo Kokay Morikawa

Monitoring of flexible oil lines using FBG sensors

Thorough the last two decades, oil and gas reservoirs discovered and developed in deep and ultra deep waters have continuously posed challenges to petroleum exploration and production activities in offshore basins. Maintaining optimum flow rates of oil and gas from subsea wellheads to surface processing facilities demands new technological solutions for petroleum companies operating in such frontiers. Integrity assurance of structures, equipment, and flow lines plays a major role in maximizing offshore production systems availability while at the same time keeping safety, operational, and environmental risks at minimum levels. In this scenario, implementation of permanent health monitoring solutions must take into account the environment of oil and gas production facilities, where installations in hazardous classified areas require explosion and fire-proof instrumentation. In this context, optical fiber sensors offer an attractive alternative to electrical sensing technologies, which, until now, have been the primary choice by maintenance personnel at offshore production units.

New Techniques for Integrity Management of Flexible Riser-End Fitting Connection

As the operation water depth for flexible risers increases, the stress level in these structures also increases. This higher load, associated with stress concentration close to end fitting, can induce fatigue damage in tensile armors at riser top section. Progressive rupture of wires due to fatigue, which may be accelerated by corrosion, is an important indication of deterioration in riser-end fitting connection, and has become a typical failure mechanism for flexible riser top section. In order to mitigate the progression of these damages, apart from the inspection program and the surface monitoring procedures already implemented, techniques for the early detection of failure mechanisms at the riser-end fitting connection, specially at the tensile armors, are under development. This paper describes and evaluates these techniques, such as visual torsion monitoring, detection through acoustic emission of tensile armor wire rupture, electromagnetic tensile armor stress measurement and monitoring through optical fiber sensor extensometers, as well as reports the results obtained from field experience.Copyright

Flexible riser monitoring using hybrid magnetic/optical strain gage techniques through RLS adaptive filtering

Flexible riser is a class of flexible pipes which is used to connect subsea pipelines to floating offshore installations, such as FPSOs (floating production/storage/off-loading unit) and SS (semisubmersible) platforms, in oil and gas production. Flexible risers are multilayered pipes typically comprising an inner flexible metal carcass surrounded by polymer layers and spiral wound steel ligaments, also referred to as armor wires. Since these armor wires are made of steel, their magnetic properties are sensitive to the stress they are subjected to. By measuring their magnetic properties in a nonintrusive manner, it is possible to compare the stress in the armor wires, thus allowing the identification of damaged ones. However, one encounters several sources of noise when measuring electromagnetic properties contactlessly, such as movement between specimen and probe, and magnetic noise. This paper describes the development of a new technique for automatic monitoring of armor layers of flexible risers. The proposed approach aims to minimize these current uncertainties by combining electromagnetic measurements with optical strain gage data through a recursive least squares (RLSs) adaptive filter.

Application of Piezoelectric Materials for Monitoring the Growth of Defects in Structures

This paper presents the results of an experimental investigation on the use of piezoelectric materials as a technique for monitoring the growth of defects in structures. The method consists of exciting the structure with piezoelectric actuators while recording the electromechanical responses from sensors placed close to the defect. The piezoelectric sensors detect the damage growth or an incipient defect by monitoring changes in the dynamic strain field, induced by the piezoelectric actuator, near the defect. This technique was evaluated through experiments using an aluminum frame structure. Results show that the piezoelectric active method is capable of detecting small changes in defect depth.

Monitoring Fatigue Crack Growth in Fracture Mechanics Specimens with Piezoelectric Sensors

This paper presents the results of an experimental study on the application of piezoelectric dynamic strain sensors for monitoring the crack growth in fracture mechanics specimens. The performance of the piezoelectric sensors was assessed through fatigue crack propagation tests in three point bend (TPB) specimens and compact tension (CT) specimens. Piezoelectric sensors of lead zirconate titanate (PZT) were placed close to the crack edge of TPB specimens and piezoelectric polyvinilidene fluoride polymer (PVDF) was bonded to the back face of CT specimens. The piezoelectric sensors detect the crack growth by monitoring changes in the dynamic strain field of the specimen. In its simplest mode, the piezoelectric sensors behave like dynamic strain gages, with the main advantage of having a high sensitivity which allows detection of lower strain levels and lower increase in crack length.

Simple tunable pulsed laser system for quasi-distributed sensors

A simple interrogation system for semi-distributed fiber Bragg grating (FBG) sensor array with a tunable pulsed laser is demonstrated. The pulsed light source is used to discriminate, in space or in time, the FBG position. The sensor array can then be constituted with low reflectivity FBG (<5%) and with the same wavelength (the FBGs have to be spatially separated). This improvement increases the capacity of the tunable pulsed laser system interrogation, which can reach up to 1000 sensors in one single fiber. The signals are measured with only one photodetection system, which makes detection less dependent of intensity variations and minimizes external influences on the circuit, such as variations in the environment temperature. A test approach has been assembled for the interrogation of five sensors in the same fiber, varying its reflectivity from 0.8% to 1.6% and with the same nominal wavelength.