UFC 3-240-13FN
25 May 2005
Table 4-9. Assessing Corrosion Rates in Cooling Water Systems:
90-Day Corrosion Coupon Test
Metal
mpy
Comment
<1
Excellent
> 1 to 3
Good
Mild steel piping
> 3 to 5
Fair
> 5 to 10
Poor
> 10
Unacceptable
Excellent
< 0.2
Good
> 0.2 to 0.5
Mild steel Hx
Fair
> 0.5 to 1.0
tubing
Poor
> 1.0 to 1.5
Unacceptable
> 1.5
< 0.1
Excellent
> 0.1 to 0.2
Good
Copper and
> 0.2 to 0.3
Fair
copper alloys
> 0.3 to 0.5
Poor
> 0.5
Unacceptable
<2
Excellent
> 2 to 4
Good
Galvanized steel
> 4 to 8
Fair
> 8 to 10
Poor
> 10
Unacceptable
< 0.1
Acceptable
Stainless steel
> 0.1
Unacceptable
NOTE: Determine pitting on coupons by visual observation; any pitting is unacceptable.
4-5.5
Corrosion Control Methods. In cooling water systems, two basic
techniques are used to provide corrosion protection to the metals that the water
contacts: use of chemical corrosion inhibitors, and raising the pH of the cooling water.
Figure 4-19 illustrates the effect of pH on the corrosion rate of mild steel. Most military
cooling water systems contain components fabricated primarily of copper alloy and mild
steel. Galvanized steel is present in galvanized cooling towers and stainless steel may
be present in piping. As the cooling water pH is increased (ideally to within the range of
8.0 to 9.5), copper and mild steel corrosion rates will decrease as shown in Figure 4-19,
although very high pH levels are corrosive to copper. The increase in pH alone cannot
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