this paper proposes a method of modeling stress in pressurized boiler components for the use in a boiler life monitoring system and/or in life-extending control. A lowdimensional model of stress components at critical locations is obtained by a suitable approximation of the underlying partial differential equations. A typical boiler component, e.g., a steam header, is spatially large with repeated elements. The proposed method is based on splitting the component into elementary parts, modeled separately as n-port systems and then obtaining the overall model as an interconnected network. The interconnection is done on a finite set of frequencies to avoid the complexity escalation. Transfer function is then fitted on the frequency-domain data. The resulting model is of low order with a good agreement with a finite element model.