Definite Mechanical Signature of Corroded Ductile Iron Pipe Flanges: Revealed through Tensile Data Analysis

Based on structural stressing-state theory, this study reveals the tensile behavior of corroded ductile iron pipe (CDIP) flanges under different degrees and types of corrosion from experimental strain data. First, the measured strains are transformed into the generalized strain energy density values as state variables, which are then used to construct numerical models and parameters that characterize the stressing states of the flanges under tension. A refined clustering analysis (CA) criterion is subsequently developed to detect mutation points in the evolution of these stressing-state parameters. These mutation features are further verified by examining the evolution curves of the stressing-state modes. The mutation points define the starting point of the flange’s failure process and the elastoplastic branch point of the flange’s normal working process, aligning with the natural law of transition from quantitative to qualitative change in physical systems. These two characteristic points are deterministic and consistently present in the experimental data of tensile CDIP flanges, reflecting a fundamental law of structural mechanical behavior. Furthermore, corrosion leads to a nonmonotonic trend in the failure load, which first increases and then decreases, allowing for the definition of a corrosion parameter. Therefore, this study challenges the prevailing view that structural working processes lack deterministic, physics-governed characteristic points. As a result, the characteristic points offer a new foundation to improve and optimize the present design codes of structures such as tensile CDIP flanges.