This study investigates the leakage problems of forged aluminum shaft seals in cracking gas compressors under alkaline conditions (pH=10.5). Through chemical corrosion kinetics analysis and engineering practices, the corrosion-thermomechanical coupling failure mechanism was elucidated. Results indicate that the corrosion rate of aluminum in alkaline environments reaches 0.25 mm/month, while the thermal expansion coefficient mismatch between forged aluminum (2.4×10^-5/℃) and steel shaft (1.2×10^-5/℃) causes a fluctuation rate exceeding 30% in labyrinth clearance, leading to seal performance degradation. Polyetheretherketone (PEEK) was proposed to replace forged aluminum. Its superior corrosion resistance (<0.01 mm/a), low friction coefficient (0.2), and excellent thermal compatibility (2.2×10^-5/℃) can significantly enhance sealing reliability. Field applications confirmed that PEEK shaft seals reduce leakage rates by 98%, decrease annual maintenance costs by 82.4%, extend service life from 8 months to no less than 5 years, and eliminate unplanned downtime, providing practical basis for the optimization of industrial sealing systems.