Autonomous underwater inspection of submerged pipelines is challenging due to confined geometries, turbidity, and the scarcity of reliable localization cues. This paper presents a minimal-sensing strategy that enables a free-swimming underwater robot to center itself and traverse a flooded pipe of known radius using only an IMU, a pressure sensor, and two sonars: a downward-facing single-beam sonar and a rotating 360 degree sonar. We introduce a computationally efficient method for extracting range estimates from single-beam sonar intensity data, enabling reliable wall detection in noisy and reverberant conditions. A closed-form geometric model leverages the two sonar ranges to estimate the pipe center, and an adaptive, confidence-weighted proportional-derivative (PD) controller maintains alignment during traversal. The system requires no Doppler velocity log, external tracking, or complex multi-sensor arrays. Experiments in a submerged 46 cm-diameter pipe using a Blue Robotics BlueROV2 heavy remotely operated vehicle demonstrate stable centering and successful full-pipe traversal despite ambient flow and structural deformations. These results show that reliable in-pipe navigation and inspection can be achieved with a lightweight, computationally efficient sensing and processing architecture, advancing the practicality of autonomous underwater inspection in confined environments.

翻译：水下淹没管道的自主检测面临诸多挑战，包括空间受限、水体浑浊以及可靠定位信息稀缺。本文提出一种最小化传感策略，使自由游动的水下机器人仅利用一个惯性测量单元（IMU）、一个压力传感器和两个声呐——一个向下发射的单波束声呐与一个旋转360度声呐——即可在已知半径的充水管道中对中并穿行。我们提出一种计算高效的方法，从单波束声呐强度数据中提取距离估计值，从而在噪声和混响条件下实现可靠的管壁检测。通过闭式几何模型融合两个声呐的测距数据以估计管道中心，并采用自适应置信度加权比例-微分（PD）控制器在穿行过程中保持对中。该系统无需多普勒速度计程仪、外部跟踪设备或复杂的多传感器阵列。在直径46厘米的淹没管道中，使用Blue Robotics BlueROV2重型遥控水下航行器进行的实验表明，尽管存在环境水流和结构变形，系统仍能实现稳定的对中并成功完成全程管道穿行。这些结果表明，通过轻量级、计算高效的传感与处理架构，能够实现可靠的管道内导航与检测，从而提升了受限环境下自主水下检测的实用性。