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chloride concentration and the molybdenum and
nickel contents.
In respect to nickel content, resistance to SCC
is minimum at some intermediate value, with it being greater at both lower and higher nickel
contents. That intermediate value is the nominal
content for the 300 series austenitics.
Molybdenum, however, has a dramatic posi-
tive effect on the SCC resistance.
Duplex alloys exhibit higher SCC resistance
due to the beneficial effects of ferrite and the low
nickel content.
Published results show that for chloride con-
raining media, the high Molybdenum austenitic
alloys are, at least, as good as the duplex alloys,
whereas the 300 series grades have poor resist-
ance.
4.3. Summary
Alloy 885 has consistently been produced
with a PREN from 39 to 40, exceeding the
minimum specified by Glover.
Alloy 885 is processed to conform to a CF of
35 or greater.
The amount of ferrite phase is optimized.
Maximum benefit is provided (strength) without
increasing susceptibility of forming undesirable
sigma phase, hard and cause of embrittlement.
A low carbon content (below 0.03%) reduces
the susceptibility of the alloy to sensitization.
The addition of nitrogen further impedes carbide
precipitation. Material can be welded with no
post weld heat treatment.
The alloy has a structure of approximately
85% austenite and 15% ferrite for ease of pro-
cessing.
This material shows, therefore, excellent per-
formance in cold and warm seawater environ-
ments due to its high localized corrosion resist-
ance. The stress corrosion cracking resistance is
also high. It is easy to process and weld.
5. Operating performance
We have analysed some performance para-
meters, more specifically, pump efficiency,
turbine efficiency and specific consumption, i.e. kWh/m 3 of product.
For the size of trains under consideration
(2,500 mVd and above), for a feed water to
permeate conversion around 45%, those para-
meters, today, are within the values shown in
Table 2.
Table 2
High-pressure train - performance level
Train size, Pump Turbine KWh/m 3 of
mVd efficiency, % efficiency, % product
2,500 80-82 84-86 3.56-3.37
5,000 81-83 85-87 3.47-3.28
7,000 83-85 86-88 3.27-3.10
10,000 84-86 87-88 3.17-3.02
Flowserve has approximately 220 trains of
these sizes in operation or under construction.
That is a total installed production capacity of
about 950,000mVd. Operating hours accumulated
year to date are close to 7.5 million.
6. Conclusions
There is a clear trend for high-pressure trains
of larger size. For a given plant size it reduces