# Review of Structural Health Monitoring Techniques in Pipeline and Wind Turbine Industries
## 6 Concluding Remarks  
The energy industry uses various infrastructures such as reactor, tank, pump, pipeline, plates, turbine, etc. Many of these parts are metallic and undergo wear and tear with time, as they carry fluids of different chemical composition as well as pass through various environmental conditions. The monitoring, repair, and maintenance of this infrastructure is extremely challenging and complex. Corrosion coupons, electrical resistance probes, etc. offer technologies to observe the damages and leaks through gadgets placed inside the conduits. They pass on certain signals and analyze the data to indicate any damage in the infrastructure or help to indicate the rate of corrosion. Generally, the techniques are average in nature and fail to precisely indicate the position of leak or damage. If it works in post processing mode, it fails to indicate the time and extent of leak. The limitation in resolutions for these techniques also restrict them to be used as predictors of damages for various parts of infrastructure. Acoustic emission or ultrasonic-type sensors offers better precision in terms of location and time of leaks; however, the technology is better applicable to see within. Point OFS, distributed OFS, etc. techniques are novel and can precisely locate the positions of leaks or damages from external positions. They also allow the prediction of damages in time ahead. However, many of these techniques fail to indicate the changes happening within. SCADA and CMS have come up with improved techniques to monitor the external damages at very high frequency. These data are required to be processed and communicated to quickly determine damages to external surfaces. These techniques are used to monitor the structural health of wind farms. UAV-based techniques have come up recently, as they offer the opportunity to scan the infrastructure externally from very close proximity. Various sensors (acoustic emission, thermal, laser, etc.) can be mounted on this airborne platform and used to determine the location of leaks or damages (Table 2). Over-ground pipelines, reactors, and tanks are easy to monitor; however, complexities increase for underground infrastructures. The extreme conditions that can be found in the oil and gas wellbore pose a certain difficulty in the monitoring of the downhole. This occurs by the presence of carbon dioxide, hydrogen, and mechanical stresses. The OFS can be relied upon for downhole sensing, but with temperatures as high as 300 degrees and hydrogen ingress, the silica fibers are dangerously affected. In addition, instrumental in this can be the presence of water, resulting in long-term instability [101]. The silica hydrogen bond with the adsorption of hydroxyl can result in extrinsic attenuation. As a counter-action to this, a hermetic carbon layer can be added for protection of the silica, but this idea would also fail at the unusually high temperatures encountered, resulting in increased importance of protective coatings [152; 153]. The alternatives for silica include sapphire cladding, which is highly expensive. If the cost can be overlooked, it normally eliminates problem and can still work at 1800 degrees. Another challenge is the transfer across long distances and across the hundreds of thousands of miles of pipeline infrastructure with high resolution. There is a common compromise between high-distance transmission and the resolution received. OFS aims to decrease this problem and lead to an optimized [104; 154; 155; 156; 157; 158; 159; 160; 161; 162]. Acoustic, OFS, and UAV-based techniques offer certain opportunities along with some challenges. It is not possible to monitor the deformations from inside as well as outside using one technology. It is required to place a sensor inside to get an early indication for impending damages or leaks expected in the future.