Failure risk assessment of pressure vessels and piping systems is an important part of their integrity management. Obviously, there are many shortcomings in risk analysis using only traditional procedures, which are mostly qualitative or conservative by nature. This study develops a novel limit analysis method using quantitative magnetic measurements to determine the failure risk of steel vessels. First, the correlation between the physico-mechanical properties of a pressurized steel cylinder and the magnetic coercive force was obtained by hydraulic tests, it is found that increasing internal pressure leads to an increase in the coercive force, and the magnetomechanical behavior can be described by a linear general expression. By solving the inverse problem, it is possible to diagnose the transition of the structure to the yield region or the fracture region based on the measurements of coercivity, which enables us to conduct the risk assessment prior to the failure of a pressurized cylinder, validated by a full-scale hydrostatic burst test. Finally, a quantitative criteria for identifying the structural failure of the pressurized cylinder was established based on coercivity measurements.