The American Society of Mechanical Engineers

78 TRANSACTIONS OF THE A.S.M.E. JANUARY, 1941
terest of turbine manufacturers in the possibility of moisture
withdrawal to the end that they will actively attack the problem
with a view to more fully realizing the advantages to be gained
therefrom.
P h i l i p S p o b n . 38 This is not only an excellent paper, broad in
scope, but also an excellent answer to those who either bemoan
lack of opportunity for making further progress in the powerproduction
field or who would prefer to go back to the days in
power-plant design when pressures and temperatures were fixed
at 200 lb and 550 F. It is also an answer to those individuals who,
without the necessary knowledge, take a set of unrelated figures
and attempt to prove that the summation of a series of coordinated
progressive steps constitutes a retrogression.
In part 1 of the paper, Figs. 2 and 3, which show so well how the
large 3600-rpm turbine and hydrogen-cooled generator have aided
the cause for higher pressure and temperature (and plant performance),
are noteworthy. Perhaps few appreciate that “it is
doubtful if it would be practical to design a 1200-rpm turbine of
reasonable efficiency to operate at 1200 lb pressure 950 F.” Perhaps
it is not common knowledge that large 3600-rpm generators
of over 25,000 kw capacity were not available before 1935.
In part 2, a striking use of comparative illustrations indicates
the development of the double shell. The top cross section of
Fig. 8 shows the front end of the Logan 40,000-kw turbine,10 the
first turbine to have a double shell. Below is shown the 60,000-kw
Windsor turbine, the first to have the “valve-in-head” design.
When each of these turbines was opened, the close clearances
found to have been maintained by the diaphragm and shaft
packings were remarkable. The bottom cross section shows the
25,000-kw turbine for the Missouri Avenue plant of the Atlantic
City Electric Company. All of these units are on the systems of
the American Gas and Electric Company.
Since it is “details” which are most important in a design,
part 3 of the paper is particularly interesting. Piping and
valve designers could well take advantage of the ideas expressed
on bolting threads, as well as the use of washers under stopvalve-bonnet
bolts. The replacement of valve-stern packings by
close-clearance metallic bushings might well be extended to more
general use.
An additional special “detail” which might be mentioned is
the initial pressure regulators developed for the Windsor and Twin
Branch turbines which protect the boilers (and, hence, the turbines)
against too great a pressure drop which might cause carryover
and too rapid cooling of drums and other thick parts. We
are also using such a regulator for the Atlantic City and Philo
turbines.
A large number of the turbines described will soon come on the
line or are already in operation. We hope that a paper will be
presented at a future meeting summarizing actual operating experience
with these, and new developments in design, resulting
from that experience.
The author points out the stabilization of design speeds at 3600
rpm for some time to come. While this is so, we hope and believe
that no stabilization will occur in other fields. Certainly, all
should maintain the same spirit of inquiry and resourcefulness
evidenced in this paper by the author and his associates. Such
an attitude will assure not only more reliable but also more
economical turbines.
A u t h o r ’s C l o s u r e
In reply to Mr. Benjamin’s comments, it would be misleading
if the results of the tests shown in Figs. 19 and 20 were compared
with the guarantees shown in Fig. 21, particularly for such small
8* Vice-President and Chief Engineer, American Gas and Electric
Service Corporation, New York, N. Y. Mem. A.S.M.E.
differences as the 1 and 2 per cent differences mentioned by Mr.
Benjamin. A companion paper presented at the same meeting
jointly with Mr. Knowlton37 is designed to permit a more definite
appraisal of the relative fuel consumptions as between
turbines of comparable design for different steam conditions,
with and without hydrogen cooling and with different leaving
losses.
It is, of course, true that the improvements due to tandem
compounding or other improved turbine-design features, low
leaving loss, and hydrogen cooling might be considered as in
competition with comparable gains which can be obtained by
higher steam conditions. However, it would seem that it might
be better to consider that on the whole these might be used to
supplement each other.
Supporting Mr. Campbell’s statement that the erosion
problem on the last-stage buckets has been relegated to “one of
secondary importance in modern turbines,” it might be of interest
to state that four last-stage buckets of airfoil section at the tip
have been in operation at 1201 fps with a theoretical moisture
content of 13 to 14 per cent for an average of 81/! years and without
sufficient erosion to warrant replacing, or any serious reduction
in efficiency. These blades did not have stellite erosion
shields.
The writer can only indorse the stand taken by Mr. Drewry
with respect to the desirability of keeping water out of a turbine
However, the fact remains that this has happened in a number
of cases in the past, even with relatively modem steam conditions
and boilers, and it has been our intention to do everything
possible in connection with the design of the turbine to minimize
the detrimental effects if it does happen. It is quite probable
that a turbine designed with these drastic conditions in mind,
if it can be designed so as to withstand such severe service, will
be a better turbine to withstand the much less severe but ordinary
variations in temperature incident to rapid load changes
and rapid starts.
Making allowance for a somewhat different use of words, the
author finds himself for the most part in agreement with the comments
offered by Mr. McCutchan. Indeed, his discussion constitutes
an amplification of the author’s very brief review of the
principles controlling high-temperature strength.
1 Chromium was not mentioned by the author because its
beneficial characteristics are effective throughout a wide range of
temperatures.
2 The author welcomes Mr. McCutchan’s more complete
statement about grain size. As a matter of fact, any adequate
discussion of this subject might well cover an entire article by
itself.
3 The objectionable dendritic microstructure referred to by
the author might perhaps better have been called dendritic segregation
or banding. It is visible to the naked eye and is altogether
different from the acicular microstructure which gives
high values of creep strength in ordinary creep tests. There is no
disagreement about these matters once the meaning of the terms
is cleared up. By duplex microstructure the author referred to
the presence of large grains and small grains at the same time, and
he is not aware that any metallurgist regards such an arrangement
as desirable.
4 The author agrees with Mr. McCutchan that a reduction
of aluminum addition from 2 to 1 lb has not gone very far in this
direction. The present evidence is that such mills as still make
these large additions of aluminum can improve the high-tem-
37 “Relative ‘Engine Efficiencies’ Realizable From Large Modern
Steam-Turbine-Generator Units,” by G. B. Warren and P. H.
Knowlton, presented at the Semi-Annual Meeting, June 17-20,
1040, of The A m e r i c a n S o c i e t y o f M e c h a n i c a l E n g i n e e r s .