Rito Mijarez

An axisymmetric guided wave encoded system for flood detection of oil rig cross-beams

A novel and completely autonomous guided wave system for flood detection in the hollow cross-beam members of offshore steel oil rigs is presented. Underwater non-destructive testing methods such as ultrasound have been used to inspect for the presence of seawater in these applications, often in conjunction with remote operating vehicles. Alternatively, a monolithic PZT guided wave transducer which can be permanently attached to a sub-sea installation and that can be powered by the action of the seawater is now being developed. Upon activation, the transducer transmits an ultrasound-encoded signal to a receiver, in the form of a real-time digital signal processing system at the surface level. Experiments have been carried out using a jointed steel pipe structure, 10 m in length, 0.5 m in diameter and 16 mm in thickness, completely immersed in seawater. The transmitter was attached to the inner wall of a spur pipe and configured to generate narrow bandwidth, low frequency ultrasonic chirp signals, coupled to the pipe as an axisymmetric mode. Results confirmed that although some attenuation occurs, the system signal processing system successfully identified the signals above the background noise.

Detection of damage in multiwire cables based on wavelet entropy evolution

Multiwire cables are widely used in important engineering structures. Since they are exposed to several dynamic and static loads as well as detrimental environmental conditions, their structural health can be compromised. Due to the critical role played by multiwire cables, it is necessary to develop a non-destructive health monitoring method to maintain their structure and proper performance. Ultrasonic inspection using guided waves is a promising non-destructive damage monitoring technique for rods, single and multiwire cables. However, the propagated guided waves are composed of an infinite number of dispersive vibrational modes making their analysis difficult. In this work, an entropy-based method to identify small changes in non-stationary signals is proposed. An experimental system to capture and post-process acoustic signals is implemented. The discrete wavelet transform is computed in order to obtain the reconstructed wavelet coefficients of the signals and to analyze the energy at different scales. The use of the concept of entropy evolution of non-stationary signals to detect damage in multiwire cables is evaluated. The results show that there is a correlation between the entropy value and level of damage of the cable including breaking of single wires and change in the mechanical contact conditions among the wires. It is found that the studied method has low sensitivity to signal noise and can reduce the computational complexity encountered in a typical time–frequency analysis.

Automatic guided wave PPM communication system for potential SHM of flooding members in sub-sea oilrigs

An automatic guided wave pulse position modulation system, using steel tubes as the communication channel, for detecting flooding in the hollow sub-sea structures of newly built offshore oilrigs is presented. Underwater close visual inspections (CVI) are normally conducted during swim-round surveys in pre-selected areas or areas suspected of damage. An acceptable alternative to CVI is a non-destructive testing (NDT) technique called flood member detection (FMD). Usually, this NDT technique employs ultrasound or x-rays to detect the presence of seawater in the tubular structures, requiring divers or remote operating vehicles (ROVs). The field-proven FMD technique, integrated within the concept of structural health monitoring, offers an alternative to these traditional inspection methods. The system employs two smart sensors and modulators, which transmit 40 kHz guided wave pulses, and a digital signal processing demodulator, which performs automatic detection of guided wave energy packets. Experiments were performed in dry conditions, inside and outside the laboratory; in the former using a steel tube 1.5 m×0.27 m×2 mm, and in the latter using a tubular steel heliport structure approximately 15 m×15 m in area and the base deck of an oilrig under construction. Results confirm that, although there was significant dispersion of the transmitted pulses, the system successfully distinguished automatically guided wave encoded information that could potentially be used in sub-sea oilrigs.

Continuous structural health monitoring guided wave PPM system using steel pipes as communication channel for flood detection in steel offshore oilrigs

An automatic guided wave pulse position modulation system, using steel tubes as communication channel, for detecting flooding in the hollow sub‐sea structures of offshore oilrigs is presented. The system employs two smart PZT‐based sensors and modulators and a demodulator based on a PZT transducer, a DSP and a microcontroller. Experiments performed in a tubular steel heliport structure and the base of a deck of an oilrig under construction, have successfully distinguished automatically guided wave encoded information.

Continuous structural monitoring of oil rig sub-sea structures for flood member detection using axisymmetric guided waves

An axisymmetric guided wave system for detecting flooding in the hollow sub‐sea structures of offshore steel oil‐rigs is presented. A sensor, attached to a sub‐sea structure and powered by seawater, transmits chirp‐encoded signals to a monitoring real‐time digital signal processing system at surface level. Experiments performed using a jointed steel pipe structure, 7 m × 0.5 m × 16 mm, completely immersed in seawater showed optimal performance at 38 kHz contrasted to 21 kHz, corroborating values predicted by disperse theoretical model.

Permanently Attached Single PZT Guided Wave Encoded Sensor for Flood Detection of Oil Rig Crossbeams

This paper presents preliminary results of a new guided wave system for detecting flooding in the hollow crossbeam members of offshore steel oil‐rigs. A sensor, permanently attached to a sub‐sea structure and powered by seawater, transmits chirp‐encoded signals to a monitoring real‐time digital signal processing system at surface level. Experiments performed using a jointed steel pipe structure, 10m×0.5m ×16mm, completely immersed in seawater showed that although attenuation was significant, the system successfully identified the signals.

A simple approach of partial discharge source location in high voltage cables

This article presents a new approach of partial discharges (PD) source location in power cables. The main advantage of this approach is the detection of the propagation direction of the PD. The method provides a pattern named by the authors PD+D, which, in contrast to the well–known phase-resolved partial discharge (PRPD) pattern, graphically shows the direction of PD propagation and uses the polarity of a sensor array on top of the magnitudes of the positive and negative parts of each PD pulse to detect the direction of propagation, is described in detail. The proposed technique is useful for the evaluation and diagnosis of power cables, since it can identify incipient faults. The attained results that demonstrate the value of this methodology and their scope and limitations are discussed.

Signal processing algorithm for thermal drift compensation in high-temperature down-hole instrumentation systems

Down-hole oil and gas industry requirements for measuring thermodynamic and geophysical parameters, for instance pressure, temperature, vibration and multiphase flow, are challenging. Accomplishing these necessities requires a complete signal communications chain of high-performance components and effective signal processing communication techniques to provide system reliability. Nevertheless, noise interference, cable attenuation and thermal drift of the front-end passive electronic elements can lead to poor signal-to-noise ratio (SNR) and possibly loss of the communication link. This paper describes a signal processing algorithm implemented in a bidirectional communication system that exchanges data from a down-hole high pressure and high-temperature (HPHT) measurement tool to the surface installation. The communication channel is a multi-conductor coaxial logging cable also used as a power supply transmission line. The instrumentation system consists of a proprietary down-hole measurement tool, composed of an HPHT sensor and a high-temperature digital signal processor (DSP)-based electronic device; located in the surface installation is a data-acquisition equipment. The system employs a signal processing algorithm, based on the frequency domain SNR characterization of the whole communication chain, which determines in real time the optimal carrier frequency that is automatically implemented in the selected modulation/demodulation technique. The obtained laboratory test results of the down-hole tool, using changes in temperature from 25° to 185°C, provide a firm basis for testing and evaluating the system in the field.

Simple Geomagnetic Induced Current Detection and Monitoring in Power Transformers

This paper presents a detection system of geomagnetic induced currents based on the measurement of the magnetic field outside the magnetic core; it is possible to evaluate the core operating conditions of power transformers under the effect of geomagnetic induced currents. The nonlinear behavior of the core due to asymmetric saturation produces a distortion in the external magnetic field which can be evaluated by the measurement of the magnitude of even harmonics; we describe the experimental setup and the instrumentation required for real-time detection of asymmetric saturation caused by quasi-DC magnetic fields. The experimental results obtained by simulating the presence of geomagnetic induced currents are presented.

Down-hole switching-mode power supply using a remote CA start up pulse

Abstract The hydrocarbon industry leans heavily upon advanced technologies to extract oil and gas from greater depths and in harsher environments. The challenge to electronics manufacturers and des...