Installed ultrasonic sensor systems are becoming more commonly used and accepted as a method to improve data integrity and increase productivity for Oil & Gas asset inspectionsespecially with underground insulated offshore and otherhard-to-access thickness monitoring locations (TMLs). Example applications where installed sensor technologies have been deployed successfully include: crude overhead lines sour water service offshore risers for sand monitoring and midstream buried pipelines. Many additional applications of these systems are anticipated to augment static thickness monitoring improve the accuracy of thicknessdata/trendingand reduce pressure-boundary penetration of conventional corrosion probes while allowingboth remote and real-time monitoring where desirable. This paper / presentation will review the development of a new flexible permanently installed monitoring system. Concepts for optimizing the measurement system will be discussed including hard-wired and wireless approaches proper transducer selection temperature compensation and statistical data analysis. A comparison of performance between dual-element and single-element ultrasonic transducers will be presented as well as field trial results on several example applications.