A Deaerator (DA) Tank is a pressure vessel found in boiler systems which removes gases (mainly oxygen) from condensate and make-up water. They generally consist of a water storage section and a deaerating/heating section. These tanks are typically made of welded carbon steel, and the residual stress of the welds coupled with the mechanical stress of operation makes them susceptible to weld cracking. Left undetected, these weld cracks can lead to catastrophic failures. In addition to the damage caused to the tank itself, catastrophic failures of a DA Tank often turn the tank into a projectile as steam and water are released from the failure resulting in additional destruction to facilities, equipment, and personnel.
Preventative measures are a good starting point when considering a maintenance program for DA Tanks. When purchasing a DA Tank, while it is generally not required, insist that all welds be stress relieved (post-weld heat treatment) in order to reduce the residual weld stress that often leads to cracking. All welds should be inspected for cracking by qualified technicians utilizing wet fluorescent magnetic particle inspection (WFMT) within five years of being placed in service, and then on a five-year cycle. This will help ensure that any cracking caused by operating stress can be detected and repaired prior to a catastrophic failure.
While there are monetary and time costs associated with timely inspection and repair schedules, these costs are minimal when considering the costs associated with a single unscheduled repair resulting from a catastrophic failure. It is very important that these thanks be properly maintained from both a reliability and safety consideration. For more information, please refer to the National Board of Boiler and Pressure Vessel Inspectors at www.nationalboard.org
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