MIL-HDBK-1003/7
Table 18
Relative Resistance of Most Widely Used Tube Materials to Failure
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*
*
90-10 70-30 Stainless
*
* Failure Mechanism
Admiralty
Cu-Ni Cu-Ni Steel
Titanium
*
*
*
2
4
4
5
6
*
* Erosion Corrosion
2
4
5
6
6
* Pitting (Operating)
*
4
6
5
4
6
*
* Pitting (Stagnant)
2
5
4
1
6
* High Water Velocity
*
3
4
5
6
6
* Inlet End Corrosion
*
2
3
4
6
6
* Steam Erosion
*
2
3
4
6
6
* Stress Corrosion
*
1
6
5
1
6
*
* Chloride Attack
3
6
5
1
6
* Ammonia Attack
*
2
4
5
6
6
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NOTE: Numbers indicate relative resistance to the indicated cause of failure on a scale
of 1 (lowest) to 6 (highest).
Freshwater Service. The most commonly used tube materials for freshwater
7.3.3.1
service are Type 304 stainless steel (ss), 90-10 copper nickel and, to a lesser extent,
Admiralty metal. Stainless steels, both type 304 and 316, provide excellent resistance
to all forms of corrosion in fresh water. However, stainless steels are susceptible to
biofouling, and scale buildup can also be a problem. Almost all failures of stainless
steel tubes, because of corrosion, can be traced to the problem of tube fouling
(including seawater applications). Type 304 stainless steel is a good selection for
freshwater makeup cooling tower systems. Stainless steel provides a good resistance to
sulfide attack, but the chloride levels must be kept low. For 304 stainless steel,
chlorides less than 1500 mg/L should be acceptable.
Copper alloys have also been used successfully in freshwater applications.
Their main advantage over stainless steels is better resistance to biofouling.
Admiralty and 90-10 copper-nickel have been used in both once-through and recirculating
freshwater cooling systems. Admiralty provides good corrosion resistance when used in
freshwater at satisfactory velocities (less than 8 fps), good biofouling resistance,
good thermal conductivity and strength, and some resistance to sulfide attack.
Admiralty is susceptible to stress corrosion cracking if ammonia is present. Admiralty
should not be used in the air removal sections. Admiralty is also susceptible to
dezincification. Because copper alloys are susceptible to ammonia based stress
corrosion cracking, to blockage induced erosion/corrosion, and to deposit related
attack, stainless steel (Type 304) is the best tube material for freshwater once-through
or recirculating cooling water systems.
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