Abstract Blockages occur in pressure sensing lines in nuclear power plants due to solidification of boron, sludge, and accumulation of other contaminants. This paper investigates the impact of sensing line blockages on the pressure system transfer function based on an equivalent pi model. For both whole-length and localized blockage scenarios, the first resonant peak tends to shift toward a lower frequency while reducing the peak magnitude. Higher frequency resonant peaks may move to either higher or lower frequencies depending on the blockage type. The lower frequency peaks start to vanish when the impulse line cross-sectional area shrinks. Operational steam pressure noise data from a nuclear power plant are analyzed and are found to compare well to simulation results from the sensing line model. Utilization of the resonant peak frequency and peak interval deviations in the operational data power spectral density is introduced in this paper. This work can be employed to achieve predictive maintenance of sensing lines so that plant operation is not disturbed.