Non-metallic materials such as polyethylene pipelines and glass fiber-reinforced epoxy composites are widely used in energy infrastructure due to their corrosion resistance, mechanical properties, and cost-effectiveness. However, premature failures in buried and externally exposed components are often attributed to thermal or oxidative aging, while biological deterioration remains largely overlooked. Although bacteria are well known to cause microbiologically influenced corrosion (MIC) in metallic systems, the analogous process in non-metallic materials, referred to as microbiologically influenced degradation (MID), particularly driven by filamentous fungi, has received limited attention. This study aimed to characterize the degradation mechanisms associated with fungal colonization of polymeric and composite materials used in energy distribution systems. Failure analyses were conducted on polyethylene and glass fiber-reinforced epoxy pipelines exhibiting external surface deterioration under field conditions, integrating documented case studies provided by the Corporación para la Investigación de la Corrosión (CIC, Colombia). The methodology included visual inspection, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mechanical testing (tensile strength and hardness), along with physicochemical analysis of soils in contact with the pipelines. Fungal isolation from pipe surfaces and adjacent soils was performed to confirm active colonization. SEM analysis revealed surface alterations such as erosion, damage, and wear. FTIR results showed oxidative degradation with the appearance of –OH and C=O functional groups. Mechanical testing indicated variations in tensile strength and hardness, while TGA and DSC analyses showed changes in degradation behavior and the presence of secondary compounds not associated with the original material. Soil conditions favored microbial growth, supporting fungal utilization of polymeric materials as a carbon source. These findings demonstrate that fungal-driven MID can significantly affect the durability of non-metallic infrastructure components and should be incorporated into integrity management and risk assessment strategies.