At the maintenance of hydraulic pipe system during continuous operation in many industrial plants, an ice plug technology for temporary partial isolation is generally applied. We have been developing ice plug technology in order to apply to nitric acid pipe systems. As chemical reagents such as nitric acid possess volume shrinkage characteristic in contrast to water, we implemented mock-up test in order to study specific freezing process of nitric acid and application ability of the ice plug technology.
Consequently, we confirmed nitric acid transferred completely to white solid phase around -60 °C to -70 °C. Furtehrmore, in mock-up test, approximate 40 °C of freezing point depression originated from freezing concentration process of nitric acid was observed. It did not affect ice plug formation, it was possible to form ice plug possessed sufficient pressure resistance performance with freezing completion time of estimated freezing process.

The residual plastic strain in ferromagnetic structural components will affect the structural integrity, the mechanical properties of materials and even the service life. Therefore, accurately characterizing the degree of residual plastic strain is important to predict the service life time of components. The plastic deformation changes the dislocation density and the magnetic hysteretic properties of ferromagnetic materials. The variation in the shape of magnetic hysteresis curves will be suitable indicators for nondestructive evaluation of the residual plastic deformation in ferromagnetic steels. The core issue is to find stable magnetic parameters a that are sensitive to the changes of the residual plastic strain. In this study, the performances of the magnetic parameters (including coercive force H_c, maximum magnetic flux density B_max, hysteresis loss W_L and the harmonic amplitudes of magnetic flux density b₁, b₃) to the residual plastic strain in low carbon steel were investigated by experiments. Especially, the influences of excitation frequency on the performances of magnetic parameters in characterizing the residual plastic strain were analyzed. The results show that both the parameters of B_max and b₁ demonstrate linear dependency on the residual plastic strain ε_p even the frequency of the applied magnetic field changes. Therefore, the parameters of Bmax and b₁ are preferred parameters to characterize the residual plastic strain in the tested low carbon steel.