A comparative analysis of inspection results for underground crude oil transmission pipelines was conducted using two diagnostic methods: Metal Magnetic Memory Non-Contact Magnetic Diagnostic (MMM-NCMD) and ultrasonic inline inspection tools (ILI). The results demonstrate that both methods provide complementary information on pipeline condition. The MMM- NCMD method enables identification of stress concentration zones within the pipeline wall, which is critical for prioritizing indications obtained from ILI inspections. Ultrasonic ILI tools exhibit limitations in detecting defects in circumferential welds and discontinuities oriented at large angles (greater than 15–20°) relative to the pipeline axis. The ultrasound-based testing method used to detect cracks parallel to the pipeline axis has limitations related to the pipeline wall thickness. In pipeline walls less than 6 mm thick, detection is practically zero. Although MMM- NCMD is a qualitative method, it significantly enhances the interpretation of ILI results. The study confirms that MMM- NCMD is an effective complementary diagnostic technique for assessing the operational condition of underground crude oil transmission pipelines.