This work reports an ultrasonic strip waveguide with distributed sensors using convergent-divergent notch reflectors for pipe surface temperature measurements. A FEM (Finite Element Method) study was performed to find the suitable notch dimensions using the S0 (longitudinal) wave mode while considering uniform reflected signal amplitude/strength from each notch of the distributed sensors' waveguide. A thin-strip waveguide flattened surface improves surface contact with the transducer, effectively enhancing wave propagation and absorbing the surrounding temperature changes. It can be efficiently laid/aligned on the measuring region of interest in the cylindrical or planar surface. A single shear transducer typically transmits and receives the S0 wave mode in the waveguide as a pulse-echo approach. We fabricated the distributed sensors' waveguide as a helical configuration based on the pipe diameter (measuring region of interest). This sensor coupled securely to the pipe surface due to the self-stiffness effect of the sensor's helix configuration. Then, the time-of-flight difference (δToF) was initially obtained from the reflectors at various temperatures to calibrate the sensor with co-located thermocouples data. Furthermore, multiple heating experiments were conducted on the pipe to ensure the sensor's repeatability. The developed helical strip waveguide sensor is easy to use, simple in design, durable, and inexpensive for in situ temperature monitoring of insulated/coated pipes in power plants, oil, and petrochemical industries.