JOHNSON CONTROLS
86
FORM 160.67-O2
ISSUE DATE: 10/9/2020
SECTION 7 - PREVENTIVE MAINTENANCE
STEAM PURITY/TURBINE DEPOSITS
Overview
It is generally recognized that the performance and re-
liability of a steam turbine can be adversely affected by
the admission of contaminated steam. When contami-
nants enter the turbine with the steam supply, the usual
result is the accumulation of deposits, either inert or
highly reactive, depending on the contaminants pres-
ent. If the contaminants are reactive, they can cause
serious damage by corrosive attack on the turbine ma-
terials.
To avoid these deposits, adequate boiler water chem-
istry control and other precautions are required along
with the need for constant surveillance during opera-
tion and inspections. When deposits or material attack
are noted during inspections, investigations into the
nature and origin of contaminants should be conducted
and a program for corrective action begun
STEAM PURITY
Deposits and harmful ions come from additive chemi-
cal elements in boiler feedwater. Make-up water for
many steam systems utilizing Murray turbines is in-
dustrial grade water which contains dissolved and sus-
pended contaminants which must be removed prior to
use in the steam system.
To avoid the likelihood of adverse effects from depos-
its and harmful ions, limits shown in Table 7 are estab-
lished for steam turbines. These limits are based on
operating history and recommendations from various
consultants. Their maintenance will ensure protection
of the turbine.
Warranty may be void in the event opera-
tional failure is attributed to inadequate
boiler feed water treatment.
EFFECTS OF DEPOSITS AND HARMFUL
IONS ON TURBINE
Efficiencies in a steam turbine are sensitive to surface
finish because of the high velocities and sharp turning
that are required by the design. While corrosion and
stress corrosion problems are unusual in steam plants,
such problems can result from boiler carry-over due
to inadequate de-aeration and boiler feed-water treat-
ment.
The chloride ion that is present in most industrial wa-
ter, can cause stress corrosion problems, but most typi-
cally it is associated with the pitting of turbine blades
and nozzles, especially in the presence of oxygen.
DETECTION OF DEPOSITS
Indication of the accumulation of deposits in the steam
path could include:
• Increased stage pressure.
• Reduced power output.
• Increased active thrust with increased oil or bear-
ing temperatures in the thrust bearing.
• Excessive vibration
If deposits are observed in the turbine during inspec-
tion, samples should be taken and submitted for chemi-
cal analysis by a laboratory to determine their make-up
and what action is required to remove them from the
system.
DETECTION OF CORROSION
Indications of corrosion may be difficult to determine.
A steam turbine’s efficient performance dictates that
it’s steam path possess tight corners and crevices.
These areas can be susceptible to pitting due to the col-
lection of condensate that possesses harmful ions.
The turbine’s blade and first stage nozzles should be in-
spected during scheduled shutdown using a bore scope.
If possible the upper half casing should be removed,
under supervision of a YORK Service Representative
for better inspection.
Pitting of the blades and nozzles is evidence of a cor-
rosive attack, making them susceptible to stress cor-
rosion cracking. YORK Service should be consulted
prior to the restart of the turbine. If residue or conden-
sate is present in the turbine and corrosion is present,
samples of the residue or condensate should be submit-
ted for chemical analysis to determine the presence of
excessive chlorides and other harmful ions.
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