# Review of Structural Health Monitoring Techniques in Pipeline and Wind Turbine Industries
## 3 Health Monitoring in Corrosion
### Distributed OFS for Chemical Sensing
 } & It uses FBG-based external & & & & & \\  & point sensors to determine & & & & & \\  & & change in temperature and & & & & \\  & & strain. The pressure wave & & & & \\  & & generated transmits both the & & & & \\  & & directions from point of & & & & \\  & for corrosion & & & & & \\  & & leakage, where the pressure & & & & \\  & & sensors detect the leakage & & & & \\  & & point by analyzing the & & & & \\  & & pressure wave & & & & \\ \hline \multirow{8}{*}{8} & \multirow{8}{*}{\ \begin{tabular}{c} Distributed OFS \\ for Physical \\ Sensing \\ \end{tabular}  } & \multirow{8}{*}{ \begin{tabular}{c} Parameters of corrosion and \\ leaks are determined by \\ temperature change due to \\ seals. Optical fibers are \\ wound over the pipe to \\ detect the leak \\ \end{tabular}  } & Determination of & & & & & \\  & & & & & & \\  & & & & &  
Figure 14: (**a**) Transmission spectra of optical fiber pH senor coated with localized surface plasmon resonance (LSPR) Au-nanoparticles-incorporated SiO\({}_{2}\) layer at different pH; and (**b**) pH sensing results from silica matrix coatings embedded with a variety of optically active materials. Reproduced with permission from [124] Copyright 2014 The Royal Society of Chemistry. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**SI No** & \begin{tabular}{c} **Name of SHM** \\ **Technique** \\ \end{tabular} & **Nature of Technique** & **Applicable** & **Precision of Damage** & \
\begin{tabular}{c} **Use for** \\ **Water-Based or** \\ **Oil-Based conduit** \\ \end{tabular} &
\begin{tabular}{c} **Potential to Predict** \\ **Future Damages** \\ \end{tabular} \\ \hline
14 & \begin{tabular}{c} Infrared \\ Thermography \\ \end{tabular} & \begin{tabular}{c} Remote sensing of cracks and \\ by thermal photogrammetric \\ camera \\ \end{tabular} & For tall structures and & \begin{tabular}{c} Easy to use and fast \\ response time for \\ covering detected \\ objects into visual \\ images \\ \end{tabular} & \
\begin{tabular}{c} Detection of \\ pipeline \\ temperature \\ variations \\ \end{tabular} &
\begin{tabular}{c} Detect leaks with \\ infrared picture \\ techniques to detect \\ pipeline \\ temperature \\ \end{tabular} \\ \hline
15 & LiDAR Sensing & \begin{tabular}{c} LIDAR sensing for small \\ cracks by LiDAR scanner \\ \end{tabular} & \begin{tabular}{c} For oil and gas \\ pipelines as well as \\ minor cracks detection \\ for civil \\ infrastructures \\ \end{tabular} & \
\begin{tabular}{c} In the absence of any \\ temperature variation \\ between the gas and the \\ environment, the leaks \\ can be detected \\ \end{tabular} &
\begin{tabular}{c} The pulsed laser is \\ used for methane \\ detection as a \\ light source for gas \\ pipelines \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 13: (**a**) Demonstration of distributed water detection in air based on the swelling-induced strain changes interrogated with an optical backscatter reflectometer (OBR). The first water drop was added at 1 min, and the second water drop was added at 30 min [71]; (**b**) Phase shift-based optical fiber sensor (OFS) without any additional coating for simultaneous multi-parameter monitoring including ionic strength as a corrosivity indicator [71].