Deaerators vessel

In smaller boiler systems, the FW tank often acts as a common condensate receiver, MU water heater, and deaerating vessel. As such, the tank is subject to the same corrosion problem risks that befall deaerators, economizers, and FW lines. Smaller systems often are inadequately designed and constructed, with the result that they may suffer serious oxygen corrosion in a particularly short time. (It is not unknown for tank wall perforation to occur within 3 to 6 months of the installation of a new FW tank as a result of pitting corrosion.)... 

This would draw water out of the deaerator vessel. 

Equipment found to suffer from cracking included tanks, absorbers, carbon treater drums, skimming drums, and piping. All welds of deaerator vessels in carbon steel should be post-weld stress relieved to minimize cracking and pitting. (Bond)5... 

The milk is usually delivered in the cooled tank (at least — 8 °C of a milk truck. For purification, it is fed into a clarifier (self-cleaning disk separator) via a deaerating vessel. These separators can process either cold or warm milk (40 °C) at speeds of 4500-8400 rpm with throughput capacities of up to 50,0001/h. 

Two deaerator vessels with associated boiler feed-water 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. 

Deaerator vessel and storage tank A were inspected. All tray sections were removed from the deaerator. With the exception of the top head-to-shell weld in the deaerator, all internal welds were ground smooth and magnetic particle inspected. No cracks were found. 

Corrosion damage was limited to minor pitting of the bottom head in the deaerator vessel. Inspection of deaerator vessel B revealed cracking at one weld. Tray sections were removed from the deaerator vessel, and shell welds were grit-blasted. Except for the top head-to-shell weld in the deaerator, all internal welds in both B nnits were then ground smooth and magnetic particle inspected. Three transverse cracks were found at the bottom circumferential weld in the deaerator vessel. These were removed by grinding to a depth of 1.5 mm (0.06 inch). 

Unlike deaerator vessel A, it was noted that none of the spray nozzles in deaerator vessel B was operational at the time of inspection. In addition, two valves had fallen to the bottom of the deaerator vessel. The bottom section of trays in deaerator vessel B had fallen to the bottom of the storage vessel. Corrosion damage in deaerator vessel B was limited to underdeposit pitting attack at circumferential... 

The cracks described in this example are very similar to those found in many other investigations, despite a variety of deaerator vessel designs and operating conditions. Cracks typically display the following characteristics ... 

All welds in deaerator vessels should be postweld stress relieved. Operational upsets should he avoided, and water chemistry must be maintained within acceptable limits. This is especially true with regard to water oxygen levels, which should be kept low to minimize pitting corrosion. 

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