PSI - Issue 70

T. Ramya et al. / Procedia Structural Integrity 70 (2025) 469–476

470

1. Introduction The cold water pipe has a diameter of 0.63 m, made of High Density Poly Ethylene. It carries the deep sea cold water from a depth of about 400m to a sump that is installed at a depth of about 5m. Typical length of this pipe varies between 700-1200m and depends on the availability of the 400m water depth near the island and that of 10-12 o C deep sea water (Rognoni et al. (2008)). The pipe is welded in island lagoon, fitted with necessary attachments and installed at the site, after making the final connections. Low-Temperature Thermal Desalination (LTTD) plants rely on deep sea cold water for the condensation process to produce freshwater (Natarajan et al.(2002)).The intake system comprises a deep-sea cold water pipe that follows an inverse catenary profile, with its rear end hold by dead weights, while the intermediate section, extending from approximately 20 m depth and remain free to move in response to oceanographic conditions as shown in figure 1.(Kathiroli et al.(2006)). In the proposed monitoring approach, the pipeline's structural response, particularly strain variations, will be measured under prevailing environmental conditions using FBG based fiber optic sensors (Hubbard et al.(2021) and Aibinu et al.(2021)). This technique makes it possible to evaluate pipeline behavior in real time, offering vital information about performance & stability in an offshore environment .

Fig.1. Typical configuration of Cold water pipe

For monitoring the strain behavior of cold-water pipelines, FBG-based fiber optic sensors are recommended because of their following advantages like inherent sensor identification, insensitivity to losses, signal stability, multiplexing, good resistance to humidity and suitable to high pressure. The structure's health can be assessed using a variety of techniques, one of which is structural health monitoring, or SHM. Recent advancements in fiber optic sensor technology have made fiber optic sensors crucial for tracking the condition of structures. Fibre Bragg Gratings are created at specific time interval by exposing the optical fiber core to a powerful ultraviolet radiation. This exposure causes variation in the refractive index of the core at specific region. This permanent change in refractive index is influenced by various physical factors including vibration, strain, temperature and pressure. For sensing applications, FBG can be used to quantify a variety of physical parameters by tracking the resulting changes in reflected wavelength. Hence, by fixing the FBG strain sensor in the cold-water pipeline using clamps, the strain experienced on the pipe can be calculated.