Practical System for Monitoring Current Stress and Accumulated Fatigue of Vessel Hull using Nondestructive Method, by Measuring Magnetic Properties of the Metal, the Coercive Force

摘要

Bearing capacity of the hull is primarily determined by its longitudinal strength. There are always a number of critical cross-sections along the length of the hull, which are structural concentrators of stresses caused by loading by goods carried, the irregularity of their placement, as well as the wave load. The magnetic characteristic of metal, the coercive force, is now the most effective informational parameter for practical assessing of fatigue in conjunction with monitoring of the current stresses. Several compact transducers in areas-concentrators allow monitoring both the current strength and assess the degree of fatigue. The system of transducers helps improving safety of loading and unloading works, as well as safety of navigation allowing choosing that direction of movement, in which the wave impact load on the hull in the critical sections does not exceed the permissible boundary values. There is a 10-year experience in monitoring several types of "river-sea" class vessels in the process of transportation, as well as in the optimization of repair works (detection of areas losing capability to resist the working load, with the assessment of the degree of reduction of capacity after repair and replacement of strengthening elements in such concentrator areas). At the same time can also be isolated the weakest link in the structure. Based on its current coercimetric state and the known boundary value for the brand of metal from which the hull is made, is predicted residual life calculated from the known from monitoring rate of fatigue-type degradation of metal. The proposed monitoring system is simple, reliable and convenient in the specific conditions of seagoing vessel operation.