ASTM D8323-20

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D8323 − 20
Standard Guide for
Management of In-Service Phosphate Ester-based Fluids for
Steam Turbine Electro-Hydraulic Control (EHC) Systems
This standard is issued under the fixed designation D8323; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The intent of this guide is to provide a summary of management practices for in-service phosphate
ester-based fire-resistant fluids used in steam turbine electro-hydraulic control (EHC) applications.
Users may also review ISO 11365 and other related publications for additional information (1-5).
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This guide provides recommendations to achieve safe
mendations issued by the World Trade Organization Technical
and reliable operation of EHC systems, recommended levels
Barriers to Trade (TBT) Committee.
for required corrective action, and suggested management
practices.
2. Referenced Documents
1.2 The recommended set of physical and chemical proper-
2.1 ASTM Standards:
ties of triaryl phosphate esters and their limits have been
D445 Test Method for Kinematic Viscosity of Transparent
selected based on past operating experience with various fluids
and Opaque Liquids (and Calculation of Dynamic Viscos-
(primarily xylylated and butylated triaryl phosphate esters)
ity)
used in different EHC system designs under different operating
D664 Test Method for Acid Number of Petroleum Products
and environmental conditions.
by Potentiometric Titration
1.3 This guide is not intended to replace Original Equip-
D892 Test Method for Foaming Characteristics of Lubricat-
ment Manufacturer (OEM) specifications but rather support
ing Oils
users experiencing operating problems by recommending lim-
D974 Test Method for Acid and Base Number by Color-
its based on existing knowledge of triaryl phosphate ester
Indicator Titration
degradation mechanisms. This guide should be used outside
D1169 Test Method for Specific Resistance (Resistivity) of
the warranty period or in cases where no OEM standard exists
Electrical Insulating Liquids
or is available.
D1298 Test Method for Density, Relative Density, or API
Gravity of Crude Petroleum and Liquid Petroleum Prod-
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this ucts by Hydrometer Method
D1500 Test Method forASTM Color of Petroleum Products
standard.
(ASTM Color Scale)
1.5 This standard does not purport to address all of the
D3427 Test Method forAir Release Properties of Hydrocar-
safety concerns, if any, associated with its use. It is the
bon Based Oils
responsibility of the user of this standard to establish appro-
D4052 Test Method for Density, Relative Density, and API
priate safety, health, and environmental practices and deter-
Gravity of Liquids by Digital Density Meter
mine the applicability of regulatory limitations prior to use.
D4057 Practice for Manual Sampling of Petroleum and
1.6 This international standard was developed in accor-
Petroleum Products
dance with internationally recognized principles on standard-
D4175 Terminology Relating to Petroleum Products, Liquid
Fuels, and Lubricants
This guide is under the jurisdiction of ASTM Committee D02 on Petroleum
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
mittee D02.C0.01 on Turbine Oil Monitoring, Problems and Systems.
Current edition approved June 1, 2020. Published July 2020. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
D8323-20. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8323 − 20
D4293 Specification for Phosphate Ester Based Fluids for ing the level of contamination by solid particles
Turbine Lubrication and SteamTurbine Electro-Hydraulic ISO 4407 Hydraulic fluid power – Fluid contamina-
Control (EHC) Applications tion – Determination of particulate contamination by the
D4898 Test Method for Insoluble Contamination of Hydrau- counting method using an optical microscope
lic Fluids by Gravimetric Analysis ISO 6247 Petroleum products – Determination of foaming
D5185 Test Method for Multielement Determination of characteristics of lubricating oils
Used and Unused Lubricating Oils and Base Oils by ISO 6618 Petroleum products and lubricants – Determina-
Inductively Coupled Plasma Atomic Emission Spectrom- tion of acid or base number – Colour-indicator titration
etry (ICP-AES) method
D6224 PracticeforIn-ServiceMonitoringofLubricatingOil ISO 6619 Petroleum products and lubricants – Neutraliza-
for Auxiliary Power Plant Equipment tion number – Potentiometric titration method
D6304 Test Method for Determination of Water in Petro- ISO 9120 Petroleum and related products – Determination
leum Products, Lubricating Oils, and Additives by Cou- of air-release properties of steam turbine and other
lometric Karl Fischer Titration oils – Impinger method
D6595 Test Method for Determination of Wear Metals and ISO 10050 Lubricants, industrial oils and related products
Contaminants in Used Lubricating Oils or Used Hydraulic (Class L) – Family T (Turbines) – Specifications of triaryl
Fluids by Rotating Disc ElectrodeAtomic Emission Spec- phosphate ester turbine control fluids (Category ISO-L-
trometry TCD)
D6971 Test Method for Measurement of Hindered Phenolic ISO 11365 Petroleum and related products – Requirements
and Aromatic Amine Antioxidant Content in Non-zinc and guidance for the maintenance of triaryl phosphate
Turbine Oils by Linear Sweep Voltammetry ester turbine control fluids
D7042 Test Method for Dynamic Viscosity and Density of ISO 11500 Hydraulic fluid power – Determination of the
Liquids by Stabinger Viscometer (and the Calculation of particulate contamination level of a liquid sample by
Kinematic Viscosity) automatic particle counting using the light-extinction
D7596 Test Method for Automatic Particle Counting and principle
Particle Shape Classification of Oils Using a Direct ISO 15597 Petroleum and related products – Determination
Imaging Integrated Tester of chlorine and bromine content – Wavelength-dispersive
D7669 Guide for Practical Lubricant Condition Data Trend X-ray fluorescence spectrometry
Analysis ISO 20764 Petroleum and related products – Preparation of
D7690 Practice for Microscopic Characterization of Par- a test portion of high-boiling liquids for the determination
ticles from In-Service Lubricants by Analytical Ferrogra- of water content – Nitrogen purge method
phy ISO 20823 Petroleum and related products – Determination
D7720 Guide for Statistically Evaluating Measurand Alarm of the flammability characteristics of fluids in contact with
Limits when Using Oil Analysis to Monitor Equipment hot surfaces – Manifold ignition test
and Oil for Fitness and Contamination 2.3 EN Standards:
D7843 Test Method for Measurement of Lubricant Gener- EN 14077 Petroleum products – Determination of organic
ated Insoluble Color Bodies in In-Service Turbine Oils halogen content – Oxidative microcoulometric method
using Membrane Patch Colorimetry 2.4 IEC Standards:
D8112 Guide for Obtaining In-Service Samples of Turbine IEC 60247 Insulating liquids – Measurement of relative
Operation Related Lubricating Fluid permittivity, dielectric dissipation factor (tan d) and d.c.
E659 Test Method for Autoignition Temperature of Chemi- resistivity
cals 2.5 DIN Standards:
DIN 51794 Testing of mineral oil hydrocarbons – Determin-
2.2 ISO Standards:
ing of ignition temperature
ISO 760 Determination of water – Karl Fischer method
(General method)
3. Terminology
ISO 2049 Petroleum products – Determination of colour
3.1 For definitions of terms used in this standard, refer to
(ASTM scale)
Terminology D4175.
ISO 3104 Petroleum products – Transparent and opaque liq-
uids – Determination of kinematic viscosity and calcula-
4. Significance and Use
tion of dynamic viscosity
4.1 This guide outlines the requirements for monitoring the
ISO 4405 Hydraulic fluid power – Fluid contamina-
performance of in-service fire-resistant fluids based on triaryl
tion – Determination of particulate contamination by the
gravimetric method
Available from European Committee for Standardization (CEN), Avenue
ISO 4406 Hydraulic fluid power – Fluids – Method for cod-
Marnix 17, B-1000, Brussels, Belgium, http://www.cen.eu.
Available from International Electrotechnical Commission (IEC), 3, rue de
Varembé, 1st floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, https://
Available from International Organization for Standardization (ISO), ISO www.iec.ch.
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Available from Deutsches Institut für Normung e.V.(DIN), Am DIN-Platz,
Geneva, Switzerland, http://www.iso.org. Burggrafenstrasse 6, 10787 Berlin, Germany, http://www.din.de.
D8323 − 20
phosphate esters to accomplish safe and reliable operation of combustion. The rate of charge generation is dependent on a
turbine electro-hydraulic control systems. number of factors including flow rate, the electrical properties
of the fluid (that is, conductivity), fluid temperature, viscosity,
5. Safety Precaution
whether the equipment is grounded, the materials of construc-
tion and the dimensions of pipework or components through
5.1 Fire safety tests are used to measure and describe the
which the fluid is flowing. If the charge on the component is
properties of phosphate esters in response to heat and flame
not dissipated, it will accumulate until it is high enough to
under controlled laboratory conditions and may not accurately
discharge to a part that is at lower potential, producing a spark.
represent the hazard of the fluids under actual fire conditions.
7.1.3 Thermal breakdown occurs in the absence of oxygen.
5.2 Fires that have occurred in operating turbines have
Depending on the phosphate structure and temperature, differ-
usually been caused by fluid or vapors contacting hot surfaces.
ent degradation pathways will occur. However, pure thermal
For example, fluid that may spill and be absorbed into
breakdown in industrial applications is unlikely as oxygen is
unprotected thermal insulation can experience an exothermic
normally present in the fluid.
reaction resulting in a rapid temperature increase. The ignition
of the absorbed fluid can occur at temperatures below the fluid 7.2 Attempting to reduce the fluid’s degradation rate will be
autoignition or manifold ignition temperatures. difficult if the system design, system operating conditions and
applied maintenance encourage oxidation to take place or
6. Requirements for Fresh Fluid
allowsmoistureingress.Insuchcases,thefluidmayneedtobe
replaced or subjected to bleed-and-feed more frequently.
6.1 Specification D4293 provides requirements for the fresh
Alternately, design changes can be made to improve fluid life.
fluid. Alternative, users may check ISO 10050 for require-
Finally, auxiliary equipment may also be used to remove
ments.
degradation products.
7. Fluid Deterioration
8. Fluid Conditioning System
7.1 Phosphate esters can degrade in several ways. In
general, three main degradation processes (that is, hydrolysis,
8.1 To achieve safe and reliable operation of EHC systems,
oxidation, thermal degradation) are responsible for the genera-
the triaryl phosphate ester hydraulic fluid should be kept clean,
tion of a wide variety of breakdown products.
with a low water content and acidity. To accomplish this, EHC
7.1.1 A common form of phosphate ester degradation is
systems generally have a fluid conditioning system with an
hydrolysis. In the presence of water, aryl phosphate esters tend
acid scavenging filter, operating continually.
to break down into their constituent acids, phosphoric acid
8.2 The principle behind the fluid conditioning system is
derivatives and phenols. The hydrolysis reaction is not usually
that the rate of acid removal must be greater than its rate of
rapid at ambient temperatures but accelerates with increasing
production. If not, control of fluid degradation is lost and
temperature and is catalyzed by the presence of stronger acids
acidity can increase quickly because of autocatalytic reactions.
and some metals.
In such a scenario, fluid life will be considerably shortened.
7.1.2 Another common form of degradation is oxidation. It
There is also a greater chance of operational problems. The
is a free radical process occurring as the fluid reacts with
goaloftheconditioningsystemisnotonlytheremovalofacid,
oxygen. Depending on heat level, oxidation of triaryl phos-
but also keeping the fluid dry and clean.
phate esters occurs via three mechanisms: ‘Low’ temperature
8.3 There are several different types of purification media
(<~200 °C) oxidation produces varnish precursors that even-
that have been used in EHC systems.
tually precipitate; ‘Moderate-high’ temperature (~300 °C to
1000 °C) oxidation or incomplete combustion occurs as a 8.3.1 For many years, fuller’s earth (an attapulgus clay
result of micro-dieseling or wasted energy through internal based on aluminosilicates) was used to treat phosphate esters.
valve leakage; and, ‘Extremely high’ temperature (>1000 °C)
It allows for removal of active chemical species, thus effec-
oxidation arises from static discharge (6, 7). tively controlling both fluid acidity and resistivity. It can also
7.1.2.1 Varnish is the result of the precipitation/deposition adsorb moisture from the fluid, but if other means are not used
of degradation compounds (also known as varnish precursors) to keep the system dry, its acid scavenging capacity will be
arising primarily from the breakdown of hydrocarbons and sacrificed. Fuller’s earth’s main disadvantage is that, when
phosphates. exposed to fluids with high acidity, it can release calcium and
7.1.2.2 The mechanism of micro-dieseling involves the magnesium. These contaminants can then form metal soaps or
rapid adiabatic compression of air bubbles in the system pump. salts that may precipitate from the fluid and form sticky
Thecompressionoffluidinthepresenceofairbubblesleadsto gels/deposits in servo-valves, pencil filters, the auxiliary filtra-
an instantaneous temperature increase in the bubble. These tion system, and other system components. If an EHC system
high temperatures lead to the formation of incomplete com- is exposed to fuller’s earth purification treatment over long
bustion products. periods (for example, several years), users should inspect their
7.1.2.3 The result of excessive internal valve leakage is reservoirs for gels or deposits, or both. These can occur on the
known to be another thermal degradation mechanism, resulting sides as a bathtub-like ring, on the bottom or they may be
in fluid darkening and the formation of degradation products. floating. It is also important that the particulate filter (that is,
7.1.2.4 Static discharge, as a result of flow electrification, the ‘polishing filter’) downstream of the acid scavenging filter
occursatextremelyhightemperatures,resultinginoxidationor shouldhavearatingsufficienttopreventfinesfromgettinginto
D8323 − 20
the EHC system (for example, finer than the main pump 9. Flushing the Hydraulic Portion of EHC Systems
discharge filter). They can be changed together with the acid
9.1 Flushing is another form of corrective action that allows
scavenging filter, based on OEM guidelines, or experience
EHC systems to be maintained in safe and reliable condition.
based on pressure drops.
There are a multitude of different flushing techniques used to
8.3.2 An alternative adsorbent for low-pressure systems
clean EHC systems and this guide will cover only the rinse
without servo valves and without resistivity limits is activated
flush and cleaning agent flush processes. These flushes require
alumina. It can contain sodium aluminate leading to the release
a detailed plan, appropriate equipment and an agreed-upon end
of sodium ions and species containing aluminum hydroxide
point. The procedure and equipment required depend on the
linkages.Thesecontaminantscaninteractwithacidphosphates
system design, the extent of any fluid degradation and the
contributing to foaming problems.Activated alumina can have
desired objectives. It is not possible to have a generic proce-
a wider particle size distribution than fuller’s earth and its hard
dure to cover all eventualities. Turbine OEMs may also have a
particlescanbeabrasive.Ifused,preferenceshouldbegivento
flushing procedure for new systems that can provide a good
a low-sodium type.
starting point.
8.3.3 An alternative option to fuller’s earth and activated
9.2 Rinse Flush:
alumina is a mixture of dried alumina with aY-zeolite (sodium
9.2.1 Asystem rinse flush may be required when EHC fluid
aluminosilicate).Thismaterialiscommerciallyavailableandis
is contaminated with large amounts of mineral oil, which
effective at low levels of acidity but less-so at higher levels
reducesitsfireresistance.Inaddition,itmayalsobeperformed
when compared to fuller’s earth. One advantage is that it does
when the system is accidently contaminated with large
not contain either magnesium or calcium, however, sodium is
amounts of water or particles. It may also be performed during
still present. Some fluid suppliers recommend that sodium
a change of fluid type or after major work on the EHC system,
aluminosilicate adsorbents not be used on fluids previously
or both. A system rinse flush that includes steam valve
treated with fuller’s earth. In the absence of recommendations
actuators requires the servo and solenoid valves to be removed
from a fluid supplier, users are advised to perform bench tests
and flushing valves installed in their place. If the steam valve
to verify that fluid properties are not negatively impacted when
actuators are removed during a system rinse flush, then
considering a change from one adsorbent media type to
flushing jumpers can be installed at the fluid piping. Emer-
another.
gencytripcircuitsareflushedusingflushingvalvesorjumpers.
8.3.4 Ion-exchange resins are another purification medium,
Accumulators must be exercised multiple times to remove
generally based on a divinylbenzene or polystyrene core, or
foreign material or degradation by-products that may be
both, onto which different functional groups have been intro-
trapped. System pumps can be used to perform this process if
duced. These functional groups can react with other chemicals
suction strainers are used to protect the EHC pumps. Suction
leading either to an exchange of ions or to the adsorption of the
strainers must be checked regularly. To increase the flow
chemicals onto their surface. A large number of different
velocity using the system pumps, both pumps are generally
ion-exchange resins are commercially available. These resins
used. Before using the system pumps to perform a flush, it is
are mainly used in water-treatment applications. Users are
extremely important to identify the type and level of contami-
therefore advised to consult with resin providers who have
nation in the system. If foreign material enters the EHC system
experience in phosphate ester applications. The main advan-
pump suction, catastrophic failure can occur and additional
tage of ion-exchange resins is that different resin types can
metal contamination will be introduced through the case drain
remove stronger or weaker acids, metal soaps and organic
line. This applies to pressure compensated pumps. External
varnish.Consequently,acombinationofdifferentresintypesat
flushing units ensure that system pumps are protected. The
different ratios can be used to address specific problems.
rinse flush process may be performed with the operating fluid
Resins can also treat significantly degraded triaryl phosphate
aslongasthefluidconditionisinspecification,withnohistory
ester fluids (8). It is important to make sure that the resin or
of high acid number, water and low resistivity values.
combination of resins used meets the requirements for control
Alternatively, specific rinse flushing fluid may be provided by
of acidity and resistivity.
the fluid supplier.
8.3.5 Long-term application of optimized ion-exchange res-
9.2.2 Steps of Rinse Flush:
ins will increase the resistivity of the fluid (9).
9.2.2.1 Draining and inspecting the reservoir.
8.3.6 Some ion-exchange resins can have as much as 50 %
9.2.2.2 Installing flushing valves in place of servo/solenoid
water. In these instances, a separate treatment must be used to
valves.
address moisture problems. Other ion-exchange resins are
9.2.2.3 Refilling with flushing fluid.
available in dried forms to prevent any significant moisture-
9.2.2.4 Cycling actuators and accumulators.
ingression during their use.
9.2.2.5 Continuous fluid sampling. An in-line or on-site
8.4 Users with EHC systems employing fuller’s earth,
particle counter can be helpful.
activated alumina, or sodium aluminosilicate, or combinations
9.2.2.6 Draining and inspecting the reservoir after flushing.
thereof, should periodically inspect the bottom of their reser-
9.2.2.7 Replacing all system filters.
voirsforgelsordepositsformedfrommetalsoaps.Theseusers
are also advised to include metals analysis in their fluid 9.2.2.8 Refilling the EHC reservoir with new fluid that has
condition monitoring. been verified to be in specification.
D8323 − 20
9.2.2.9 System start up and verifying EHC system operation 10. Condition Monitoring Program
and fluid condition. Typically, samples are taken between 72 h
10.1 The principle behind the fluid conditioning system is
to 96 h after fluid recirculation.
that the rate of acid, moisture, and particle-removal must be
greater than the rate of their production or ingression. There
9.3 Cleaning Agent Flush:
are, however, occasions where the fluid may deteriorate at
9.3.1 A system cleaning agent flush should be performed
faster rates due to changes in operation, environment, or
when users need to remove gel/varnish or heavy soot from
maintenance, or combinations thereof.Also, from an economic
thermal degradation found in the system. These deposits can
pointofview,thefluidmayreachastagewhereitsreplacement
formwhenahighacidnumberisnotcorrectedforlongperiods
is the preferable option. Therefore, to avoid uncontrolled fluid
(for example, more than three months). Reservoir inspections
deterioration and maintain the safe and reliable operation of
can be done to identify these deposits or an MPC test may help
EHC systems, users must implement a condition monitoring
to determine the amount of suspended varnish or soot in the
program to assess fluid condition and implement appropriate
fluid. The right cleaning agent flush process can dissolve
corrective actions.
depositsandputtheminsolution,allowingthemtoberemoved
from the reservoir. This process should be performed by a
10.2 Due to the scope of this guide, only the most critical
professional that has extensive knowledge of EHC system
physical and chemical fluid properties will be discussed. Other
operation and experience with that specific cleaning agent.
materials are available such as from some turbine OEMs,
External flushing units should be used to perform this process
EPRI, and VGB (1-5).
due to the high amount of contamination generated during the
10.3 It is good practice to filter fluid when transferring from
flush. EHC system pumps have a greater chance of failing if
drums into the turbine EHC system. The rating of the filter
used to perform this process. This process requires removing
element should be as good or better than the system filter
all servo and solenoid valves from the system, and installing
element. In extreme cases, it may also be necessary to dry the
flushing valves on the actuators. Emergency trip solenoids are
fluid before operation. Note that triaryl phosphate ester fluids
removed and flushing valves are installed on the trip manifold.
have a low viscosity index and become more viscous at low
Accumulators are removed from the system and disassembled
temperatures. Consequently, fluid in the drums should be
to inspect the piston/bladder for contamination, then reas-
allowed to warm to about 20 °C or higher. The actual tempera-
sembled with new seal kits or bladders, or both. It is very
ture will depend on the equipment used. Having a warm fluid
important to use compatible elastomers. After the cleaning
(that is, at lower viscosity) is very important in case the
agent flush process is complete, it is necessary to perform the
transferring unit filters have a pressure bypass valve. In such a
rinse flush process to remove the cleaning agent fluid, and
case, cold fluid could enter the system unfiltered.
contamination generated from this process.
9.3.2 Steps of Cleaning Agent Flush: 11. Fluid Sampling
9.3.2.1 Draining and inspecting the reservoir.
11.1 Samplingofin-servicephosphateesterfluidsshouldbe
9.3.2.2 Installing flushing valves in place of servo/solenoid
in accordance with Guide D8112.
valves.
11.2 If a fire-resistant fluid sample is required from a drum,
9.3.2.3 Refilling the system with original fluid and cleaning
then the sample should be represented by an “all-levels
agent.
sample” obtained by tube sampling.Additional information on
9.3.2.4 Cycling actuators.
sampling is available in Practice D4057.
9.3.2.5 Removing and inspecting accumulators, and re-
11.3 Care should be taken to ensure that the fluid is mixed
building them if required.
properly before samples are drawn and that the samples are
9.3.2.6 Continuous fluid sampling. An in-line or on-site
representative of the whole charge.
particle counter can be helpful.
11.4 Sampling intervals should be specifically set for dif-
9.3.2.7 Draining fluid at all low points, including heat
ferent EHC systems depending on their criticality and the
exchangers, and inspecting the reservoir after the cleaning
severity of their operating conditions. Users are advised to
agent flush process.
refer to OEM instructions or other regulatory guidelines for
9.3.2.8 Refilling the EHC reservoir with rinse flush fluid.
guidance in selecting appropriate sampling intervals. In the
9.3.2.9 Performing the rinse flush process.
absence of specific directions, users are advised to take
9.3.2.10 Continuous fluid sampling until fluid samples ex-
samples as follows:
ceed OEM or user specifications.
11.4.1 Upon receipt of a new fluid per Specification D4293.
9.3.2.11 Draining fluid at all low points.
11.4.2 After a new fluid charge has been in circulation for at
9.3.2.12 Cleaning the reservoir.
least 24 h. Typically, samples are also taken between 72 h to
9.3.2.13 Replacing all system filters.
96 h after fluid recirculation.
9.3.2.14 Reinstalling accumulators and recharging with ni-
11.4.3 On a monthly basis for testing as outlined in Table 1.
trogen.
11.4.4 On a annual basis for testing as outlined in Table 1.
9.3.2.15 Refilling the EHC reservoir with new fluid.
11.4.5 Prior to outage or significant maintenance action.
9.3.2.16 System start up and verifying EHC system opera- 11.4.6 After a fluid has been returned to circulation (pref-
tion and fluid condition. Typically, samples are taken between erably for 72 h to 96 h) following an outage or significant
72 h to 96 h after fluid recirculation. maintenance action.
D8323 − 20
TABLE 1 Suggested Tests and Frequency of Routine Condition Monitoring Program for In-Service Triaryl Phosphate Ester Fluids Used
in EHC Systems
A
Property / Frequency Test Method Alternative Method Monthly Annually As Required
(Troubleshooting)
Appearance See 12.1 ISO 2049 × ×
ASTM Color D1500 ××
Acid Number D664 or D974 ISO 6619 or ISO 6618 × ×
Water Content ISO 760
D6304 ××
ISO 20764
B
Volume Resistivity D1169 IEC 60247 × ×
Fluid Cleanliness ISO 4405
ISO 11500
ISO 4407 ××
ISO 4406
D7596
Metal Content D4898
××
D6595
Membrane Patch Colorimetry (MPC) D7843 ××
Linear Sweep Voltammetry D6971 ××
Viscosity ISO 3104
D445 ×
D7042
B
Chlorine Content EN 14077
See 12.12 ×
ISO 15597
Air Release D3427 ISO 9120 × ×
Foaming D892 ISO 6247 × ×
Mineral Oil Content See 12.8 ××
C
Manifold Ignition Temperature See 12.15 ISO 20823 ×
C
Auto-Ignition Temperature E659 DIN 51794 ×
A
Annual tests can be deferred but for trending or to get a benchmark for troubleshooting, or both, they should be run at least every few years or prior to and following
a scheduled major outage, or both.
B
For lower pressure systems without servo valves, resistivity and chlorine testing are not typically necessary.
C
Manifold Ignition and Auto-Ignition tests are usually performed after specific concerns are identified.
12. Recommended Practices for Fluid Condition 12.2.1 Some darkening of triaryl phosphate esters can be
Monitoring normal as a result of oxidation, micro-dieseling or thermal
degradation, or both.
12.1 Appearance:
12.2.2 Color is typically determined by Test Method D1500
12.1.1 Anappearancecheckoffluidsamplesisanimportant
with a range from 0.5 (for example, colorless) to 8 (for
screening test and an initial indicator of fluid and system
example,almostblack).Somesamplesmaybetoodarkormay
conditions. It allows users to identify if any significant change
not match color standards. In this case, they are reported as
has occurred since the last sampling. Examples include fluid
“Does Not Match Standard Colors”. However, additional
clarity (for example, milky or hazy appearance due to sus-
comments should be provided to describe the color observed.
pended water, presence of air bubbles, mineral oil contamina-
Photographs can be helpful.
tion greater than the fluid solubility limit, significant contami-
12.2.3 In-service fluid will slowly darken but, typically, the
nation with fine particles, etc.), darker than normal color, free
darkening should level out after a few years, unless abnormal
water layer, and sediment. Users may also assess whether the
conditions are present.
fluid has a burnt or unusual odor.
12.2.4 If rapid or unusual darkening is detected, then users
12.1.2 Fluid samples collected in clear, colorless glass
should investigate the root cause (for example, hot spots in the
bottles are preferable. Samples in transparent plastic bottles
EHCsystem,micro-dieseling,achangeinoperatingconditions
also allow for visual assessment of fluid condition. In either
such as running two pumps at the same time, low fluid level in
case, the sample can be slowly inverted and the bottom
the reservoir, lower make-up rate, contamination, steam lines
checked for sediment. If there is a free water or mineral oil
too close to the fluid line, deteriorated insulation, etc.). An
layer, it should be at the top of the fluid sample.
infrared camera may assist in the detection of hot spots in the
12.1.3 It is a good practice to repeat the appearance check
EHC system.
after letting the samples sit overnight in a closed container at
12.2.5 After identifying the root cause of the problem,
room temperature or after 24 h in an open container. This will
corrective actions could include bleeding off a portion of the
allow entrained gases to escape, minimizing confusion be-
in-service fluid. Online treatment might also be possible but
tween air and water contamination. This also allows some
this would depend on the cause of fluid darkening. Such
particles to settle.
treatment could include the use of ion-exchange resins, acti-
12.1.4 To identify abnormal fluid, users should be familiar
vated carbon, or the use of electrostatic filtration.
with the appearance of new fluid. Therefore, an unused sample
of the fluid in current use should be retained and available for
12.3 Acid Number:
comparison. The unused fluid sample should be kept in a
12.3.1 This property is the most important parameter used
cabinet or light-proof container to prevent darkening because
for monitoring EHC fluid condition.
of UV from lights.
12.3.2 As discussed in Section 7, Fluid Deterioration, acidic
12.2 ASTM Color: compounds are a result of hydrolysis, oxidation, or thermal
D8323 − 20
breakdown, or combinations thereof. The acids that form may allow for the determination of acid strength. For trending
be stronger or weaker. Stronger acids are generally arylphos- purposes, it is recommended that results be obtained from the
same method.
phoric acids that form following hydrolytic phosphate ester
breakdown. Weaker acids may be phenols that arise from
12.4 Water Content:
hydrolysis or organic acids (for example, carboxylic acids) that
12.4.1 Water contamination causes the slow breakdown of
arise from oxidative breakdown of alkylphenols. Stronger
triaryl phosphate esters by hydrolysis, producing acid phos-
acids are more reactive than their weaker counterparts and,
phates (stronger acids) and phenols (weaker acids). A high
therefore, tend to be more harmful. The concern with high
concentration of acid phosphates in operating fluid catalyzes
acidity is that the degradation process is auto-catalytic, signifi-
the fluid degradation process. Also, the rate of hydrolysis will
cantly increasing the rate of fluid deterioration. In addition, if
increase with water content and with the temperature of the
solid media such as fuller’s earth, activated alumina, or an fluid.
alumina/zeolite blend are used in the purification system, high 12.4.1.1 Water contamination is typically the result of
ingress from the environment since phosphate esters are
acidity can form soluble metal soaps or salts. These contami-
hygroscopic and can absorb over 1000 mg⁄kg of water. Note
nants may promote foaming when in solution, or impair valve
that desiccant breathers may not be adequate to maintain
operation if precipitated. If acid number gets too high, these
desired water levels since hygroscopic EHC fluids may pull
adsorbent media may be less efficient.
moisture from breathers.
12.3.3 If weaker acids (for example, alkylphenols) are not
12.4.1.2 Water may also elute from some acid adsorbent
removed, high MPC varnish potentials may result due to
media. Many commercially available ion-exchange resins have
oxidation or thermal degradation, or both.
a significant moisture content (generally around 50 %) and the
12.3.4 It is important to understand the root cause of acid
use of a wet resin can lead to significant water ingression.
increase and to eliminate the source.
Resin providers with experience in lubricant applications will
12.3.5 Depending on their acid number, users may consider
often provide dried ion-exchange resins which eliminate or
the application of a different purification medium. While
mitigate this risk. Alternatively, some resin suppliers recom-
stronger acids are more harmful, their higher relative reactivity
mend the use of various drying technologies alongside wet
tends to make them easier to remove. Weaker acids, on the
resins (for example, reservoir dry air purge gases or vacuum
other hand, may be more difficult to remove and can accumu- dehydration). Users are advised to consult with resin suppliers
lateifanappropriatepurificationmediumisnotemployed.Itis whoareexperiencedinEHCapplicationstodeterminewhether
their resins may contribute water and, if they do, what steps
therefore important to check the level of weaker acids present.
should be taken to mitigate the associated risks.
In extreme conditions, corrective actions may require draining
12.4.1.3 Occasionally, cooler leaks may also be a source of
a portion of the in-service fluid and replacing it with new fluid.
water ingression.
12.3.6 Current operating experience with triaryl phosphate
12.4.2 If there is no evidence of abnormal water ingress,
ester fluids in EHC systems suggests that maintaining the acid
then a vacuum dehydration unit or reservoir dry gas purge can
number below 0.10 mg KOH/g will allow users to operate in
be the quickest way to dry the fluid and manage its moisture
sustainable, good condition. It may be difficult to maintain the
content. However, it is recommended that the fluid should not
acid number at this level with some EHC system designs. In
be over-dried (below 300 mg⁄kg) to avoid negative impacts on
such cases, additional purification treatments or system modi-
fluid condition.
fications to reduce operational severity should be considered.
12.4.3 Preferably, the fluid moisture level should be main-
12.3.7 Operating experience also indicates that acid number
tained in the range of 300 mg⁄kg to 500 mg⁄kg. Typically,
will increase more rapidly once its level exceeds 0.20 mg
water content of 1000 mg⁄kg is considered as the turbine OEM
KOH⁄g. Acid number increases tend to be especially rapid
maximum allowable level. Trend plots can help to identify the
when stronger acids are present. The rate of hydrolysis for
source of water ingression and the most suitable corrective
butylated phenyl phosphate esters is generally higher as
action. Seasonal variations in atmospheric humidity also influ-
compared to xylyl phosphate esters. Therefore, systems con-
ence the fluid water content, with lower levels normally being
taining butylated phenyl phosphate ester fluids may require
found in drier winter months.
more frequent replacement of acid scavenging filters as com- 12.4.4 If,duetocontamination,asignificantfreewaterlayer
pared to systems containing xylyl phosphate ester fluids under
is formed, corrective actions may include pumping or siphon-
similar conditions. ing (or other water-removal techniques) of the water floating
on the surface or in the worst-case scenario, total fluid
12.3.8 There are two standards for determination of fluid
replacement.
acidity. Test Method D664, the potentiometric method, mea-
12.4.5 If water contamination due to external ingression is a
sures total acid number from both stronger and weaker acids,
continuous problem, users should consider installing a vacuum
and can distinguish between the two. Test Method D974, the
dehydration unit, a dry gas purge system or a membrane dryer.
colorimetric method, partially measures the stronger acids and
does not measure the weaker acids. For dark in-service fluid, 12.5 Volume Resistivity:
the potentiometric method D664 is preferred because of 12.5.1 EHC systems with servo valves might experience
difficulty in identifying a definite color change for the colori-
servo valve spool corrosion due to electro-kinetic wear. While
metric D974 test method. The colorimetric method does not volume resistivity is not the only factor associated with this
D8323 − 20
wear process, it is the best available measure to predict the 12.6.6 In general, the cleaner the fluid, the better its condi-
conditions for this type of wear. In general, if the volume tion and the less likely it is to cause problems. Typically, for
resistivity is too low, fluid flow across the servo valve spool systems with servo valves, a fluid cleanliness level up to
can increase due to electro-kinetic wear. This leakage is of 16/14/11 is considered acceptable and corrective actions
great concern because system pumps may not keep up with should be initiated if the ISO Cleanliness Code exceeds a level
fluid flow demand causing potential EHC system shutdown. of 17/15/12.
The replacement of worn servo valves is costly so resistivity
12.6.7 In-service triaryl phosphate ester fluids may also
should be maintained in specification. contain significant quantities of particles below 4 µm, particu-
12.5.2 Volume resistivity is a complex phenomenon which larly sub-micron particles, which can also provide an indica-
is dependent on multiple parameters. The potential parameters tion of problems. Therefore, users operating EHC systems
affectingresistivityincludestrongerandweakeracids,phenols, experiencing problems may consider performing additional
soot particles, wear debris, dirt, metal soaps, leached metals, tests (for example, membrane patch colorimetry, Test Method
moisture, thermal degradation products and organic varnish. D4898 or ISO 4405) to monitor overall trends of sub-micron
Therefore, a holistic approach is required to address the fluid’s and <4 µm particles.
resistivity.
12.6.8 If a particle count is excessive, prompt actions are
12.5.3 The recommended test method is Test Method
necessary. Actions can include: request the lab to identify the
D1169. A test temperature of 20 °C is generally employed for particles; resample and retest; check the filter differential
this application. The test temperature should always be re-
pressures to determine if high (plugging), low (bypassing) or
ported along with the volume resistivity as it can alter the test not changing (not effective); check the main pumps for noise,
result significantly. Higher temperatures lower the resistivity.
vibration or heat; and, verify that sampling was proper (review
Users are cautioned against comparing test results obtained at procedure, container and sample point).
different temperatures or with resistivity values obtained by
12.7 Metal Content:
other test methods.
12.7.1 MetalcontentistypicallydeterminedbyTestMethod
12.5.4 Typical corrective actions include reducing fluid
D5185 (ICP/AES Inductively Coupled Plasma Atomic Emis-
acidity, improving fluid cleanliness, lowering water levels (if
sion Spectrometry) or by Test Method D6595 (Rotating Disc
elevated) and changing the adsorption medium. As noted
Electrode Atomic Emission Spectrometry). There are also
earlier, long-term application of optimized ion-exchange resins
other methods (for example, atomic absorption spectroscopy).
will increase the resistivity of the fluid (9). Online partial or
They differ not only in the manner in which the samples are
complete fluid replacement may also be considered to address
prepared for analysis but also the manner in which the spectral
low fluid resistivity values in the shorter term.
lines are observed within the instrument. In general, this
12.5.5 In general, higher volume resistivity values signifi-
analysis must always be done in a very precise fashion in order
cantly reduce electro-kinetic wear.
to obtain a meaningful result. Note that common spectroscopy
12.6 Fluid Cleanliness: equipment will not give accurate metal values if the particles
12.6.1 High particle counts in fluids from operating EHC arelargerthan3 µm(forTestMethodD5185)or8 µm(forTest
Method D6595). If larger particles are seen or suspected
systems can be a sign of existing or pending problems. It can
indicate the breakdown of fluid molecules, dust ingression, consider acid digestion as the first step, filtration and SEM-
EDS (scanning electron microscopy-energy dispersive X-ray
cross contamination of incompatible fluids, addition of inad-
equately filtered fluid or makeup fluid, component wear, spectroscopy) or analytical ferrography as outlined in Practice
D7690.
corrosion, the presence of acid adsorbing media, inadequate
system seals, the presence of metal soaps, inefficient filtration 12.7.2 New fluid has a concentration of trace metals usually
or external solid contamination. below 1 mg⁄kg per element except for phosphorous which is
one of the constituent elements in phosphate esters.
12.6.2 Suspended agglomerated species including organic
varnish and thermal degradation compounds may also result in 12.7.3 In-service triaryl phosphate ester fluids may show
particle count increases. magnesium (Mg) and calcium (Ca) from fuller’s earth, or
sodium (Na) and aluminum (Al) from alumina or an alumina/
12.6.3 Particle counts vary dependent on sampling.
Therefore, it is essential to take fluid samples from a represen- zeoliteblend.Someion-exchangeresinsmayreleasesodiumor
acidity into treated fluids; however, these resins are usually not
tative circuit of the EHC system in specially cleaned bottles
using a standardized procedure and sampling valve. If the employed in EHC applications.
result is of concern, users should verify their sampling proce- 12.7.4 High metal levels can lead to the formation of metal
dure and re-sample to get a second count. soaps upon reaction with acids. Metal soaps have a negative
12.6.4 The methods used for rating particle contamination impact on
...