NACE Task Group T-7H-7 on Deaerator Cracking was formed in 1984 to conduct an organized, in-depth study into the cause of the high incidence of serious deaerator cracking problems in steam generating plants. The task group had previously sponsored technical symposia in which several papers were published on deaerator cracking.
This standard is intended to be the primary source of information on deaerator cracking and is directed toward operators and designers of deaerator equipment used in steam generation. Information presented in this standard reflects the work of the many individuals involved in documenting the deaerator cracking problem and is based on studies of carbon steel units. In developing this standard, the task group considered the case of a southeastern U.S. paper mill that had experienced a ruptured deaerator storage tank with loss of life. The catastrophic failure resulted in an increase in deaerator inspections and widespread concern for vessel reliability and personal safety. A "Deaerator Advisory," published by the Engineering Division of TAPPI reported that 68 vessels (approximately 50% of the vessels inspected in 1983) showed cracking in welds and adjacent heat-affected zones resulting from corrosion fatigue. Of the three reported storage vessel ruptures, one resulted in fatalities and considerable plant downtime.
Other literature on deterioration of deaerators noted that investigations of various systems indicated that cracks in the welds and heat-affected zones of longitudinal and circumferential seams were the cause of some of the problems. Corrosion, another major cause, had occurred at a more rapid rate in the weld heat-affected zone in some instances, and problems had reportedly occurred in both the welds and the base metal caused by shell thinning to levels that could not support the load. Periodic internal inspections combined with nondestructive examinations were recommended to detect deaerator deterioration. Other reports of the seriousness of deaerator weld cracking also were published at this time.
T-7H-7 has continued to actively collect data and information on re-inspections. However, continued efforts will focus on surveillance of the cracking problem and updates relative to the committee's findings.
This standard recommended practice was originally prepared in 1990 by T-7H-7 under the guidance of NACE Unit Committee T-7H on Corrosion and Its Control in Steam Generating Systems and issued by NACE International under the auspices of NACE Group Committee T-7 on Corrosion by Waters. It was revised by T-7H-7 in 1996.
1.1 The objective of this section is to identify important factors influencing boiler feedwater (BFW) deaerator cracking based on literature references and case history analyses. Historical Document 1991