Abstract
Stress-assisted corrosion (SAC) forms fissures on the waterside of boiler tubes near external attachment welds. Because of the severe consequence of water leaks in black liquor recovery boilers, these fissures present a particular hazard in the pulp and paper industry. Aware of the hazard they present since the late 1980s, this industry has developed radiographic techniques to estimate their severity and empirical rules to determine the fitness-for-service of tubes containing SAC. Perhaps surprisingly, burst tests suggest that the strength imparted by external attachment welds more than compensates for the weakening effects of the internal stress-assisted corrosion fissures they produce. Although stress-assisted corrosion is closely related to corrosion fatigue cracking, which has been studied in detail by EPRI, cycle chemistry guidelines developed to avoid corrosion fatigue in utility boilers have not generally been applied in the pulp and paper industry. On the basis of information gathered at a pulp and paper industry colloquium on stress-assisted corrosion, a research program was developed to clarify the mechanisms of stress assisted corrosion (SAC) in industrial boilers and to determine the key parameters in its mitigation and control.
