Moisture is generally referred to as a chemical contaminant when suspended in lubricating oils.

Moisture is generally referred to as a chemical contaminant when suspended in lubricating oils. Its destructive effects in bearing applications can reach or exceed that of particle contamination, depending on various conditions. Like particles, vigilant control must be exercised over entry of water to minimize its accumulation in the lubricants and its damage to bearing surfaces.
This paper will discuss the influence of moisture on the chemical stability of a lubricant's additives and base stock. The effects of moisture on machine surfaces, particularly as relates to wear and corrosion, will also be discussed. Finally, a three-step, proactive maintenance strategy will be proposed to minimize the effects of moisture on lubricant and bearing life.

 http://dramarnathgiri.blogspot.in/2012/12/the-second-most-destructive-lubricant.html?q=LUBE+OIL

Fouling Factors Fouling is a function of the system and the equipment used.

Fouling Factors Fouling is a function of the system and the equipment used.  Parameters which influence the fouling rate in a system include: the type of fluid, the type of heat exchanger, the temperatures, the velocities and the materials of construction.  The actual fouling rate is different for each application.  There are numerous resources for fouling factor values.  The best source is from existing operating facilities.  When production data is available, it can be used to calculate the actual fouling factors for the system.  Together with the maintenance and cleaning history, this provides the best resource for selecting the fouling factors for a particular application. However, when production data is not available, one must rely on other sources.  Over the years, typical fouling factors have been compiled for various systems and fluids.  The tables below show some of these typical fouling factors:

Process Fluids	Fouling Resistance
	(ft2-°F-hr/BTU)
Oils
Fuel Oil #2	0.002
Fuel Oil #6	0.005
Transformer Oil	0.001
Engine Lube Oil	0.001
Gases and Vapors
Acid gas	0.002 - 0.003
Ammonia vapor	0.001
Chlorinated hydrocarbons vapors	0.001 - 0.0015
Chlorine Vapor	0.002
CO2 vapor	0.001
Compressed Air	0.001
Hydrogen	0.0005
Hydrogen (saturated with water)	0.002
Light Hydrocarbon vapors (clean)	0.001
Natural Gas	0.001 - 0.002
Natural Gas Flue Gas	0.005
Nitrogen	0.0005
Polymerizable vapors (with inhibitor)	0.003 - 0.03
Refrigerant Vapors (oil bearing)	0.002
Solvent Vapor	0.001
Stable Overhead Products	0.001
Steam (non-oil bearing)	0.0005
Steam (exhaust, oil bearing)	0.0015 - 0.002
Liquids
Ammonia Liquid	0.001
Ammonia Liquid (oil bearing)	0.003
CO2 Liquid	0.001
Chlorinated hydrocarbons liquid	0.001 - 0.002
Chlorine Liquid	0.002
DEG & TEG Solutions	0.002
Ethylene Glycol Solutions	0.002
Gasoline	0.002
Heavy Fuel Oils	0.005 - 0.007
Heavy Gas Oil	0.003 - 0.005
Hydraulic Fluid	0.001
Kerosene	0.002 - 0.003
Light Gas Oil	0.002 - 0.003
Light hydrocarbon liquid (clean)	0.001
MEA & DEA Solutions	0.002
Naphtha and Light Distillates	0.002 - 0.003
Organic Heat Transfer Liquids	0.002
Refrigerant Liquids	0.001

                                                       

Water	Fouling Resistance		Fouling Resistance
	(ft2-°F-hr/BTU)		(ft2-°F-hr/BTU)
water temperature	125°F or less		over 125°F
water velocity	3 ft/s or less	over 3 ft/s	3 ft/s or less	over 3 ft/s
Boiler Blowdown Water	0.002	0.002	0.002	0.002
Brackish Water	0.002	0.001	0.003	0.002
Condensate	0.0005	0.0005	0.0005	0.0005
Cooling Tower Water (treated)	0.001	0.001	0.002	0.002
Cooling Tower Water (untreated)	0.003	0.003	0.005	0.004
City or Well Water	0.001	0.001	0.002	0.002
River Water (minimum)	0.002	0.001	0.003	0.002
River Water (average)	0.003	0.002	0.004	0.003
River Water (muddy or silty)	0.003	0.002	0.004	0.003
Sea Water	0.0005	0.0005	0.001	0.001
Treated Boiler Feed Water	0.001	0.0005	0.001	0.001