DataSheet2_Optimally Temperature Compensated FBG-Based Sensor Dedicated to Non-Intrusive Pipe Internal Pressure Monitoring.PDF

Pipe internal pressure measurement is of utmost importance in the oil & gas industry to monitor the extraction process, and thus to prevent hydrate-plugs formation which may occur in specific temperature and pressure conditions. Traditional solutions usually rely on pressure sensors in direct contact with the fluid to monitor, therefore requiring one hole per sensor, but they also weaken the pipe structure, which may prematurely lead to significant leaks. Attempts to develop non-intrusive pressure sensors relying, for instance, on acoustic waves detection or even strain measurements (the pipe wall acting, in some way, like the membrane of a traditional intrusive sensor), are up to now not fully satisfying, mainly due to poor temperature cross-sensitivity compensation. Thus, 1 °C temperature compensation error typically leads for Fiber Bragg Grating (FBG) transducers to pressure measurement biases greater than 26% at 100 bar (e.g.: Ø 4” NPS Sch. 160 steel pipe). Consequently, if such non-intrusive, but biased, solutions could possibly have been considered to monitor, for instance, a Nuclear Power Plant (NPP) primary coolant circuit, it was with the risk of dramatic consequences since the fluid can reach temperatures up to 320 °C. On the other hand, the solution detailed here truly achieves to cancel the temperature cross-sensitivity, and potentially any additional effect on pressure measurement, provided that each effect has the same influence on all transducers. It first relies on a better understanding of the pipe behavior under hydrostatic pressure, supported by a dedicated model developed on purpose, which demonstrates that the internal pressure and the surface temperature variations of a closed pipe can be recovered with at least two direction-sensitive transducers, the temperature dependence of the pressure measurement being simply removed by a straightforward compensation process. This paper explains the underlying principle, thanks to a formal model established with only few hypotheses, but extended to more complex field conditions. It ends with a lab-test validation involving FBG transducers attached to a pressure circuit submitted to temperature variations greater than several tens of °C, and concludes about the advantages and limitations of this novel approach for non-intrusive sensing, and its potential extensions to other measurement techniques.

管道内压测量在油气工业中对监测开采流程、防止特定温压条件下形成水合物堵塞至关重要。传统解决方案通常依赖与待测流体直接接触的压力传感器，因此每个传感器需开设一个开孔，但此举会削弱管道结构，可能过早引发严重泄漏。此前尝试开发的非侵入式压力传感器，例如基于声波检测或应变测量的方案（管壁在一定程度上可充当传统侵入式传感器的隔膜），迄今尚未完全令人满意，主要原因在于温度交叉灵敏度补偿不足。以光纤布拉格光栅（Fiber Bragg Grating，FBG）传感器为例，1℃的温度补偿误差通常会导致100巴压力下的测量偏差超过26%（如公称直径4英寸SCH 160钢管场景）。因此，这类非侵入式但存在测量偏差的方案若用于监测核电站（Nuclear Power Plant，NPP）一回路冷却系统，将面临灾难性后果的风险——该系统内流体温度可达320℃。与之相对，本文详述的方案真正实现了温度交叉灵敏度的消除，且只要各影响因素对所有传感器的作用一致，即可消除压力测量中的其他附加效应。该方案首先基于对静水压下管道行为的深入理解，辅以专门开发的专用模型，证明封闭管道的内压与表面温度变化可通过至少两个方向敏感型传感器恢复，压力测量的温度依赖性可通过简便的补偿流程直接去除。本文通过仅基于少量假设建立的形式化模型阐释其核心原理，并将其拓展至更复杂的现场工况。最后通过实验室测试验证：将FBG传感器附着于承受数十摄氏度以上温度变化的压力回路中，并总结了这种非侵入式传感新方法的优势与局限，以及其向其他测量技术拓展的潜力。