This research aims to explore the evolutions of the piezomagnetic field (B field) of X80 steel under cyclic tensile stress at different piezomagnetic field measurement distances. The X80 sample was subjected to cyclic preloading with a large stress amplitude. Subsequently, a series of cyclic tensile experiments were conducted to measure the piezomagnetic fields in the vicinity of the X80 sample at pre-determined distances by a fluxgate magnetometer. It was found that the magnetic parameters of X80 steel have quantitative relationship with the piezomagnetic field measurement distance. The B field-stress curves with different maximum stresses share a same evolution trajectory during the loading process when the starting point of the loading processes stays unchanged. The unloading curves have different traces with the tendency towards the starting points. Additionally, the relationship between Tail reversals and piezomagnetic field measurement distance was also discussed in this paper. Based on the piezomagnetic signals, the stresses of the pipelines can be detected and safety problems can be also prevented.

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