Weld Cracking in Oil Refinery Deaerator
Vessels. Two deaerator vessels with associated
boiler feedwater storage tanks operated in similar
service at a refinery. The vertical deaerator
vessels were constructed of carbon steel (shell
and dished heads), with trays, spray nozzles,
and other internal components fabricated of type
410 stainless steel. Boiler feedwater was treated
by sand filtration using pressure filters, followed
by ion-exchange water softening. Hardness was
controlled at less than 0.5 ppm calcium carbonate
(CaCO3). A strong cationic primary coagulant
(amine) was used to aid the filtering of
colloidal material. Treated water was blended
with condensate containing 5 ppm of a filming
amine corrosion inhibitor. Final chemistry of
the feedwater was controlled to the concentration
limits given in Table 4. Oxygen scavenging was
ensured by the addition of catalyzed sodium
bisulfite (NaHSO3) to the storage tanks. Treated
water entered the top of the tray section of the
deaerators through five or six spray nozzles and
was stored in the horizontal tanks below the
deaerators.