25 May 2005
Table 3-12. ASME Suggested Feedwater Limits for
Marine Propulsion Water Tube Boiler
Dissolved oxygen (ppm O2) before
chemical oxygen scavenger addition
Total iron ppm Fe (as Fe)
Total copper ppm Cu (as Cu)
pH at 25 oC (77 oF)
Chemicals for pre-boiler system
Oily matter ppm
1. Makeup water percentage: Up to 5% of feedwater.
2. External treatment: at sea, evaporator condensate; in port, evaporator
condensate or water from shore facilities meeting feedwater quality
3. Assumes existence of deaerator.
4. Saturated steam purity: 30 ppb TDS maximum, 10 ppb Na maximum, 20
ppb SiO2 maximum.
5. VAM = Use only volatile alkaline materials.
Boiler Water Chemistry Limits. Tables 3-13 through 3-16 show boiler
water chemistry limits. The limits are specific for the type of boiler, operating pressure,
and steam application. There are two types of limits to recognize. The first comes from
the presence of natural constituents in the feedwater (i.e., TDS or conductivity, silica,
and alkalinity). These constituents can be the controlling factor for COC. Blowdown is
ultimately required to keep their levels within limits. SS is the result of precipitation of
minerals. These are kept within limits through bottom blowdown. The second type is
treatment limits for chemicals added into the boiler (see Tables 3-17 and 3-18).