Flood member detection for real-time structural health monitoring of sub-sea structures of offshore steel oilrigs

Abstract

A structural flood detection system for real-time health monitoring in the hollow sub-sea members of new offshore steel oilrigs is presented. Field-proven flood member detection techniques, integrated within the concept of health monitoring, offer an alternative to underwater nondestructive testing methods based on ultrasound and x-rays, which have been used to detect the presence of seawater in these applications, often with diverse or remote operating vehicles. The system employs a single piezoelectric transducer which can be permanently attached to the inner wall of every sub-sea structure and which is powered by a normally inert seawater battery. Upon activation, the sensor transmits ultrasonic chirp or tone encoded pulses, in the range of 21–42 kHz, to a monitoring receiver system at deck level for decoding and identifying flooded members. Experiments have been carried out using a jointed steel pipe structure, 7 m in length, 0.5 m in diameter and 16 mm in thickness. This structure was flooded and completely immersed in seawater. Two approaches to the system were considered during the investigation, depending on the communication channel exploited; the former utilized guided waves, on the basis of exploiting the steel structure as a wave-guide; the latter employed underwater ultrasound, based on using the seawater as a propagation medium. Although severe losses were encountered in both approaches, the system effectively identified the signals above the background noise. This work forms the foundation for the future development of a system that can be used with large, commercial offshore platforms.

Sediment microbial fuel cell powering a submersible ultrasonic receiver: New approach to remote monitoring

“…The developed SMFCs and PMSs can be used to power other underwater sensors that have power requirements similar to those of the SUR. For example, the acoustic [14,22], piezoelectric [21], thermocouple [11], optical [3], barometric [25], and electrochemical [16] sensors that are used for environmental monitoring, habitat monitoring, seismic monitoring, oceanography, and military surveillance all have power requirements that are in the range from 10 mW to 2.5 W. The main advantage of our PMS is that it can track the time of monitoring using a RTC.…”

“…There are many alternative power sources used for unattended sensors, such as seawater batteries [21], wind turbines [2,12], solar panels [1,18,27], piezoelectric energy generators [24,28], and ther-moelectric energy harvesters [6,13]. Each of these has its disad-vantages, especially for underwater sensors like the SUR.…”

Ultrasound imaging of immersed plates using high-order Lamb modes at their low attenuation frequency bands

“…A variety of emitter/receiver configurations and propagation modes are reported in the literature when considering the inspection of immersed structures. Leinov et al [25] analyzed the propagation through buried pipes to detect corrosion using a pulse-echo configuration, where the wave was excited by a ring of transducers around the pipes; Djili [27] analyzed immersed copper tubes using a similar pulse-echo arrangement, but exciting the tube with a single transducer; Mijarez et al [28] used a pitch-catch configuration with a pair of transducers for SHM of sub-sea tubular structures. The Time-Reversal technique [29] has also been used in the detection of cracks in a hollow cylinder immersed in water [30].…”

Outlier Analysis and Artificial Neural Network for the Noncontact Nondestructive Evaluation of Immersed Plates

“…Na and Kundu [7] devised a transducer holder to activate flexural cylindrical waves for damage detection in underwater pipes. Mijarez et al [8] developed a OUTLIER ANALYSIS OF IMMERSED PLATES 155 waterproof transmitter and a seawater-activated battery package to monitor the tubular cross-beam members used in offshore steel structures. Bingham et al [9] tested a pair of robots crawling along a ship hull and carrying ultrasonic transducers to send and receive guided waves along the hull surface.…”