BLOWER AS 5203550 - Caterpillar

Corrosion
Piping System Materials
Electromotive series - A list of metals whose order indicates the relative tendency to be oxidized.An excellent material for piping carrying sea water is the copper-nickel alloys. The cost makes the use of this piping unusual for all but the most critical systems. Whenever practical, use the same type of material for all the sea water piping. Piping that is made from different metals should not make contact with each other. One of the metals can corrode at a rapid rate.The materials will corrode according to their position in the electromotive series. Refer to Table 1 for corrosion rates of various metals in sea water.
Table 1
Corrosion Rates of Various Metals in Sea water    
Metal     Corrosion Rate in Quiet Sea water (1) mm/yr    
Aluminum     .02 to 1.20    
Zinc     .02 to 0.25    
Lead     .02 to 0.38    
Iron (Steel)     .10 to 0.25    
Silicon Iron     .00 to 0.07    
Stainless Steel (2)     .00 to 0.12    
Copper Alloys     .01 to 0.38    
Nickel Alloys     .00 to 0.02    
Titanium     nil    
Silver     nil    
Platinum     nil    
( 1 ) Rates are ranges for general loss in sea water at ambient temperatures and at velocities no greater than 1 m (3 ft) per second. Pitting penetration is not considered. The values shown are in millimeters per year.
( 2 ) Many stainless steels exhibit high rates of pitting in stagnant sea waterBlack iron pipe is often used in sea water service. Replacement should be planned every two or three years. If it is necessary to use pipe or other cooling system components of more than one material, avoid allowing the dissimilar metals to touch, even by mutual contact with an electrically conductive third material. Corrosion will be much more severe if a flow of electrons is able to pass freely from one of the metals to the other.Galvanic Corrosion in Sea Water
Noble metal - A metal or alloy, such as gold, that is highly resistant to oxidation and to corrosion.Electrochemical series - A list of metals that have been arranged in order of their standard electrode potentials.When two dissimilar metals are electrically connected and both are submerged in saltwater, the metals form a battery and an electrochemical reaction takes place. In this process, one metal is eroded. The rate of deterioration is proportional to a number of factors:
The differential potential between the two metals on the electrochemical series.
The relative areas of the two metals: If there is a small area of the more noble metal relative to the less noble metal, the deterioration will be slow and relatively minor. If there is a large area of the more noble metal such as copper sheathing on a wooden hull, and a much smaller area of the less noble metal, such as iron nails holding the copper sheathing to the wood, the wasting away of the iron nails will be violent and rapid.
Stray electrical