Due to the complex internal environment of pipelines and the minute dimensions of cracks, crack detection signals exhibit a low signal-to-noise ratio. To address the challenge of high-SNR detection for crack defects on both inner and outer pipeline walls, a balanced field electromagnetic crack detection method employing simultaneous clock sources for excitation and reference signals is proposed. The detection principle of balanced field electromagnetic technology for internal and external wall cracks in pipelines is elaborated. The influence of frequency difference noise between excitation and reception signals is analysed through theoretical and numerical simulations. A balanced field electromagnetic crack detection system based on FPGA digital orthogonal demodulation is developed, with software design completed for synchronising excitation and reference signals. Experimental validation confirms the system’s detection capability, demonstrating its ability to detect surface cracks ranging from 1 to 7 mm and buried cracks from 1 to 4 mm. Surface crack detection signals exhibit a single peak and valley characteristic, while buried crack signals display a double peak characteristic. Field crack detection pulling tests on pipelines demonstrated that the system consumes less than 1.1 W of power, achieving a signal-to-noise ratio exceeding 41.9 dB for surface crack detection and over 36 dB for buried crack detection. This method is suitable for inline inspection of crack defects on both the inner and outer walls of pipelines.