Experimental analysis of the obturation of pipes by ice plugs

This paper assembles together the knowledge acquired during seven tests of freezing with liquid nitrogen on pipes representing circuits in thermal or nuclear power plants, using different geometrical configurations, steels and initial conditions. These tests made it possible to link the physical phenomena to the appearance of the thermal stresses caused by the freezing. The stresses measured were below the elasticity limit. The speed of temperature fall and the thermal gradients (in the thickness, axial and azimuthal) were measured; this made it possible to define a typical transient regime that may be considered representative of a freezing operation. The tests of the resistance of the plug to pressure showed that it could withstand high pressures. The tests also led to improvements in the technology of the process and the methods used. (orig.)