Corrosion-induced Cracking

Oxygen/aluminum ratios were also determined at various locations in the cracks as indicated in Figure 7.11 and results are given in Table 7.2. The oxygen/aluminum ratio increases from 1.5 to 2.0 as the crack location moves towards the crack tip. The ratios of 1.5 and 2.0 likely represent AI2O3 and AIO2, respectively. This observation tends to indicate that corrosion induced cracking took place. 

Delamination leading to spall of cover Horizontal corrosion induced cracks Due to plane of weakness at rebar level... 

Li, C.-Q., Melchers, R.E. Zheng, J.-J., 2006. Analytical Model for Corrosion-Induced Crack Width in Reinforced Concrete Structures. Structural Journal, 103(4) 479-A87. 

Vu, K., Stewart, M.G. Mullard, J., 2006. Corrosion-Induced Cracking Experimental Data and Predictive Models. Structural Journal, 102(5) 719-726. 

Corrosion also occurs as a result of the conjoint action of physical processes and chemical or electrochemical reactions (1 3). The specific manifestation of corrosion is deterrnined by the physical processes involved. Environmentally induced cracking (EIC) is the failure of a metal in a corrosive environment and under a mechanical stress. The observed cracking and subsequent failure would not occur from either the mechanical stress or the corrosive environment alone. Specific chemical agents cause particular metals to undergo EIC, and mechanical failure occurs below the normal strength (5aeld stress) of the metal. Examples are the failure of brasses in ammonia environments and stainless steels in chloride or caustic environments. 

Intergranular corrosion-fatigue cracks in copper may he difficult to differentiate from stress-corrosion cracking. The longitudinal orientation of the cracks revealed that the cyclic stresses were induced by fluctuations in internal pressure. 

Dents in tubing can induce erosion failures, especially in soft metals such as copper and brass. Welding and improper heat treatment of stainless steel can lead to localized corrosion or cracking through a change in the microstructure, such as sensitization. Another form of defect is the inadvertent substitution of an improper material. 

Cracking mechanisms in which corrosion is implicated include stress corrosion cracking, corrosion fatigue, hydrogen-induced cracking and liquid metal embrittlement. Purely mechanical forms of cracking such as brittle failure are not considered here. 

Norco, Louisiana (Ref. 15) 7 (6 in buildings) A corrosion-induced propane leak in a fluid catalytic cracking unit resulted in an explosion that destroyed the control room. Six fatalities occurred in or near the control room the seventh was caused by a falling brick wall. 

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