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CLARKE, WHITE, UPTHEGROVE—CONDENSER TUBES AND TH EIR CORROSION 515
Condenser shells were originally made almost universally
of cast iron with flanged joints which became rather
complicated and hard to keep tight in large condensers.
With the advent of welding the use of steel-plate shells
came rapidly into vogue and today practically all condenser
shells are of welded steel-plate construction. These
are free of flanged joints and are much lighter and less
costly than the old cast-iron shells.
The exhaust connection between turbine and condenser
has always been a troublesome feature. Expansion joints
of metal or rubber have been used but they involved two
large flanged joints which were extremely difficult to
make tight in the first place and to keep tight after installation.
The joints themselves were more or less subject
to cracking with age. In other cases the shell was
bolted to the exhaust flange of the condenser and carefully
designed systems of springs were installed to carry
the weight of the condenser when there was no vacuum
in the system. The most desirable arrangement is to
hang the condenser from the turbine and weld the joint
with suitable supports provided to take the weight when
the condenser is filled with water for testing.
When the question of condensing equipment for the
extension for The Narragansett Electric Company was
under discussion, the condenser-tube problem was seen to
be of major importance. The condensing water available
is particularly bad and heretofore only jet-type condensers
have been used, so no experience has been had with tubes.
In an attempt to assure the best material for tubes, it
was decided to conduct an extensive test on various materials
in a way that would as nearly as possible duplicate
the conditions actually existing in a working condenser.
Based on such information as was available, Admiraltymetal,
aluminum-brass, and cupronickel tubes were
selected as the ones most likely to give good service. A
miniature cast-iron condenser with Muntz metal tube
plates was used, as shown diagrammatically in Fig. 1 and
tubes of each of the three materials just mentioned, as well
as a bronze tube, were installed as indicated in the cross
section. Barriers were placed in the inlet water box as
indicated, separating the sections containing the various
kinds of tubes so there could be no possibility of water
coming in contact with more than one kind of tube.
No attempt was made to vent the water spaces. River
water was passed through the tubes at a velocity corresponding
to that expected in the actual condenser installation
and blowdown water from the station 400-lb
blowdown system was admitted to the steam space.
In addition to the condenser test, an impingement
test was made. As will be seen from the diagram, Fig. 1,
the river water from the test condenser was passed
thrcrugh a small heater where its temperature was raised
to 90-110 F and then sprayed against the inner surface of
split-tube samples. It was recognized that this test did
not bear a direct relation to the conditions existing in
a condenser, but it was thought that the information
obtained might supplement that from the condenser
test. It was also felt advisable to make an impingement
test as it was a test which would produce deterioration
in the tube metal more rapidly than would be the case
from a condenser test. When the work was started, it was
believed that the time element for the condenser test would
be of the order of but a few months. Therefore, it was
essential that as much supplementary information as
possible be obtained. As a matter of fact, there proved