分佈式水下管線的光纖偵漏系統

The Distributed Fiber Optic Leak Detection System for Underwater Pipelines

水下管線常因腐蝕或外力而受到破壞，因而造成管內物質的外漏，由於洩漏地點的不確定性，使得事後偵漏的工作非常困難，傳統的偵漏方法，例如氣泡追蹤法，壓力量測法，不是徒勞無功就是誤差太大，因此，尋求新偵漏技術乃是異常迫切之務。本文提出以同軸式桑克干涉儀光纖感測系統的觀念，來改良傳統的環狀式桑克干涉儀的架構，作為分佈式水下管線洩漏位置的偵測系統，可供對水下管線洩漏的長期監測或早期預警之用，其功能也與傳統桑克干涉儀作比較，其中，包括零點頻率的準確度，光纖的使用效率等多項參數都顯示出具體的功能提升。

Underwater pipelines may suffer leakage from damage due to corrosion or external stresses. Because of the uncertainty of the leaky location, it is very tough for the after-event leaky detection. The traditional detection devices are neither failed to work nor unacceptable for its large errors. Hence it is very helpful to design a novel leak detection system. A distributed fiber optic sensing system based on the principle of the Sagnac effect used to sense time-varying physical field was proposed to detect the location of a leaky pipeline. Because the configuration of a Sagnac interferometer is a loop, it is hard to be set in real surrounding. Nevertheless, half of its length of loop fiber has to be isolated or protected from these physical fields. Hence, in this paper, an in-line conception was studied as the design goal. Its performance is compared with that of a traditional one. The results denote that several parameters, including accuracy of null frequency, efficiency of fiber usage etc., demonstrated themselves with very satisfied performance.