MIL-HDBK-1003/7
Because of the expense and potential problems with titanium tubes, 90-10
copper-nickel and 70-30 copper-nickel tubes are considered better selections for clean
seawater applications. When the seawater is also characterized by a high sulfide
concentration, the new austenitic and ferritic stainless steel condenser tube alloys
should be considered since 90-10 copper-nickel and 70-30 copper-nickel are highly
susceptible to sulfide pitting attack.
Polluted Water Service. Polluted water materials should be used whenever
7.3.3.4
sulfides, polysulfides, or elemental sulfur are present in the cooling water. Sulfides
produce and accelerate corrosion of copper alloys. Therefore, copper based alloy tubes
are not considered feasible polluted water materials. Stainless steel is also not
acceptable since the polluted water is usually brackish or seawater. This leaves
titanium and the new austenitic and ferritic stainless steels. The most acceptable of
these tube materials is titanium based mainly on its greater experience. However, the
"super" stainless steels, which were created predominantly for use with polluted cooling
water, are less expensive than titanium and are not expected to experience any of the
problems with cathodic protection systems that are possible with titanium tubes. The
majority of installations using these new "super" stainless materials are located in
coastal areas with polluted cooling water. To date, the results have been favorable for
the "super" stainless steels used in this application.
Tubesheets. In order to prevent galvanic action between tubes and
7.3.4
tubesheets, the obvious selection of tubesheet material for new units is the use of same
material as the tubes. However, this may be prohibitively expensive. The next best
choice is to use materials that are as close as possible to one another in the galvanic
series (see Figure 31) or ensure satisfactory performance by using coatings or cathodic
protection.
Freshwater Service. Tubesheet material compatible with stainless steel tubes
7.3.4.1
are carbon steel and stainless steel. Carbon steel has been used successfully for
tubesheet material. Since it is less expensive than stainless steel, it is the obvious
tubesheet material selection for use with stainless steel tubes. Muntz metal is the
most widely used tubesheet material with copper-nickel tubes. Muntz metal is also
suitable for use with Admiralty tubes.
Brackish and Seawater Service. Because of their relatively high yield
7.3.4.2
strengths, aluminum bronze and silicon bronze provide good tube-to-tubesheet joint
integrity and good pull-out strength. The materials are compatible with all copper
alloy tubes. Even if titanium tubes are used, aluminum bronze is the most common choice
for tubesheet material involving welded tubes. (Cathodic protection is required,
however.) Silicon bronze tubesheets are not widely used. Aluminum bronze is the
preferred tubesheet material for copper-nickel installations since silicon bronze is not
easily weldable and since Muntz metal does not provide as much strength. Also, as a
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