Page 403 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION DAMAGE, DEFECTS, AND FAILURES 381

expansion was sufficient in this case to break three of the bridge rivets. This type
of localized corrosion is known to be a serious derating factor when the load bear-
ing capacity of a bridge or of any other infrastructure component is evaluated during
inspection.
In some cases, the deformation because of the corrosion of aluminum in lap joints
of commercial airlines is accompanied by a bulging (pillowing) between rivets,
because of the increased volume of the corrosion products over the original material.
This phenomenon was thought to be the primary cause of the Aloha accident in
which a 19-year-old Boeing 737 lost a major portion of the upper fuselage (Fig. 5.74)
in full flight at 24,000 ft (34). The “pillowing” phenomenon in which the faying
surfaces are forced apart is schematically shown in Figure 5.75.
The major corrosion product identified in corroded fuselage joints is hydrated alu-
mina, Al(OH) , with a particularly high volume expansion (6.0) relative to aluminum
3
(0.9). Such a buildup of voluminous corrosion products can result in an undesir-
able increase in stress levels near the critical fastener holes and subsequent fracture
because of the high tensile stresses resulting from the “pillowing.”
Corrosion failures are very environmentally context specific, as well as conse-
quentially context specific. In most of the industrial equipment context, a corrosion
rate of 25 μm/year for steel is acceptable whereas such an amount of rust in the food
industry would not be acceptable.
Another example consists of the development of a burial site for storing radioactive
waste. A corrosion failure would occur if a minimum amount of radioactivity would
leach in the groundwater after about 10 to 1 million years. Failure in this case has

Figure 5.74 Boeing 737 that lost major portion of fuselage (16).