Corrosion Monitoring of Metal Components in the Beishan Underground Laboratory

Field exposure and online corrosion monitoring were carried out at China's Beishan Underground Research Laboratory (URL) to investigate steel performance for underground facilities. Q235 and Q355 steels, the main construction materials, were tested in air or in fissure water at the ramp site near the ground, 280 or 560 m underground, respectively. Coupons and U‐bend specimens were exposed to underground air, whereas selected probes were exposed either to underground air or to fissure water. Within 6 months, the average corrosion rates remained low, whereas localized attack developed progressively. The maximum pit depth reached 123.40 µm on the upward‐facing Q235 coupon at the ramp, and upward‐facing surfaces generally showed deeper pits than downward‐facing surfaces. SEM and Raman analyses revealed discontinuous, porous rust layers containing iron oxyhydroxide‐related phases. No macroscopic stress‐corrosion cracks were observed. At −560 m, atmospheric‐probe and coupon corrosion rates were of the same order, while fissure‐water exposure produced a higher probe response.