ASTM G185-06
(Practice)Standard Practice for Evaluating and Qualifying Oil Field and Refinery Corrosion Inhibitors Using the Rotating Cylinder Electrode
Standard Practice for Evaluating and Qualifying Oil Field and Refinery Corrosion Inhibitors Using the Rotating Cylinder Electrode
SIGNIFICANCE AND USE
Selection of corrosion inhibitor for oil field and refinery applications involves qualification of corrosion inhibitors in the laboratory (see Guide G 170). Field conditions should be simulated in the laboratory in a fast and cost-effective manner (1).3
Oil field corrosion inhibitors should provide protection over a range of flow conditions from stagnant to that found during typical production conditions. Not all inhibitors are equally effective over this range of conditions so that is important for a proper evaluation of inhibitors to test the inhibitors using a range of flow conditions.
The RCE is a compact and relatively inexpensive approach to obtaining varying hydrodynamic conditions in a laboratory apparatus. It allows electrochemical methods of estimating corrosion rates on the specimen and produces a uniform hydrodynamic state across the metal test surface. (2-21)
In this practice, a general procedure is presented to obtain reproducible results using RCE to simulate the effects of different types of coupon materials, inhibitor concentrations, oil, gas and brine compositions, temperature, pressure, and flow. Oil field fluids may often contain sand. This practice does not cover erosive effects that occur when sand is present.
SCOPE
1.1 This practice covers a generally accepted procedure to use the rotating cylinder electrode (RCE) for evaluating corrosion inhibitors for oil field and refinery applications in defined flow conditions.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:G185 −06
StandardPractice for
Evaluating and Qualifying Oil Field and Refinery Corrosion
Inhibitors Using the Rotating Cylinder Electrode
This standard is issued under the fixed designation G185; 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.
1. Scope G46 Guide for Examination and Evaluation of Pitting Cor-
rosion
1.1 This practice covers a generally accepted procedure to
G59 Test Method for Conducting Potentiodynamic Polariza-
use the rotating cylinder electrode (RCE) for evaluating
tion Resistance Measurements
corrosion inhibitors for oil field and refinery applications in
G96 Guide for Online Monitoring of Corrosion in Plant
defined flow conditions.
Equipment (Electrical and Electrochemical Methods)
1.2 The values stated in SI units are to be regarded as
G102 Practice for Calculation of Corrosion Rates and Re-
standard. The values given in parentheses are for information
lated Information from Electrochemical Measurements
only.
G106 Practice for Verification of Algorithm and Equipment
1.3 This standard does not purport to address all of the for Electrochemical Impedance Measurements
safety concerns, if any, associated with its use. It is the
G111 Guide for Corrosion Tests in High Temperature or
responsibility of the user of this standard to establish appro- High Pressure Environment, or Both
priate safety and health practices and determine the applica-
G170 Guide for Evaluating and Qualifying Oilfield and
bility of regulatory limitations prior to use. Refinery Corrosion Inhibitors in the Laboratory
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 The terminology used throughout shall be in accordance
D1141 Practice for the Preparation of Substitute Ocean
with Terminologies G15 and D4410 and Guide G170.
Water
D4410 Terminology for Fluvial Sediment 4. Summary of Practice
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
4.1 This practice provides a method of evaluating corrosion
sion Test Specimens
inhibitor efficiency in a RCE apparatus. The method uses a
G3 Practice for Conventions Applicable to Electrochemical
well-defined rotating specimen set up and mass loss or elec-
Measurements in Corrosion Testing
trochemical measurements to determine corrosion rates in a
G5 Reference Test Method for Making Potentiostatic and
laboratory apparatus. Measurements are made at a number of
Potentiodynamic Anodic Polarization Measurements
rotating rates to evaluate the inhibitor performance under
G15 Terminology Relating to Corrosion and CorrosionTest-
increasingly severe hydrodynamic conditions.
ing (Withdrawn 2010)
G16 Guide for Applying Statistics to Analysis of Corrosion
5. Significance and Use
Data
5.1 Selection of corrosion inhibitor for oil field and refinery
G31 PracticeforLaboratoryImmersionCorrosionTestingof
applicationsinvolvesqualificationofcorrosioninhibitorsinthe
Metals
laboratory (see Guide G170). Field conditions should be
simulated in the laboratory in a fast and cost-effective manner
(1).
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion
of Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory
5.2 Oil field corrosion inhibitors should provide protection
Corrosion Tests.
over a range of flow conditions from stagnant to that found
Current edition approved Jan. 15, 2006. Published February 2006. DOI:
during typical production conditions. Not all inhibitors are
10.1520/G0185-06.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
equally effective over this range of conditions so that is
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
The last approved version of this historical standard is referenced on The boldface numbers in parentheses refer to the list of references at the end of
www.astm.org. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G185−06
important for a proper evaluation of inhibitors to test the electrode can be attached. The other end of the rod is attached
inhibitors using a range of flow conditions. directly to the rotating unit, through which the electrical
connection is made.
5.3 The RCE is a compact and relatively inexpensive
approach to obtaining varying hydrodynamic conditions in a 6.6 After attaching the specimen to the shaft, the system
laboratory apparatus. It allows electrochemical methods of should be checked for eccentricity and wobble. This can be
estimating corrosion rates on the specimen and produces a accomplished by installing a dial micrometer so as to monitor
uniform hydrodynamic state across the metal test surface. the location of the top of the rotating cylinder and rotating the
(2-21) shaft slowly through one complete turn. The micrometer
should then be moved to monitor the center of the specimen,
5.4 In this practice, a general procedure is presented to
and the process repeated. Finally the micrometer should be
obtainreproducibleresultsusingRCEtosimulatetheeffectsof
moved to the bottom of the specimen and the process repeated.
different types of coupon materials, inhibitor concentrations,
The assembly should also be rotated at its maximum rotation
oil, gas and brine compositions, temperature, pressure, and
rate and the specimen wobble checked again using, for
flow.Oilfieldfluidsmayoftencontainsand.Thispracticedoes
example, a laser indicator or vibration monitor.
not cover erosive effects that occur when sand is present.
6.7 Appropriate cylinder specimen (such as, carbon steel) is
6. Apparatus machined and snugly fitted into the PTFE or any other suitable
specimen holder (Fig. 2). The presence of gap between
6.1 Fig. 1 shows a schematic diagram of the RCE system.
specimen and holder will create crevice corrosion as well as
The RCE apparatus consists of a rotating unit driven by a
change the flow pattern. If necessary, apply a very small
motorthatisattachedtoasampleholder.Asystemwitharange
amount of epoxy to fit the specimen into the holder. Tightly
of rotational speeds from 100 to 10 000 rpm with an accuracy
attach or screw an end-cap so that only the outer cylindrical
of 62 rpm is typical. It is essential to be able to rotate the
area of known length is exposed to the solution. The specimen
electrodeatbothlowandhighspeedsandtobeabletomeasure
holder is then attached to the rotating unit. Specimen, holder,
the speed and maintain it at a constant. The accuracy of the
and end-cap should all have the same diameter.
rotation rate should be checked. At the side of the sample
holder where it is outside the cell, electrical connections to the 6.8 The rotating unit is attached into the experimental
electrodes are made by a brush contact. It is important for the vessel, ensuring that there is no leakage through the rotating
connection to be as noise free as possible. shaft and the holder and that the rotating shaft is vertically
positioned. Even a very slight inclination could drastically
6.2 The cylinder geometry is usually defined in terms of the
change the flow pattern.
length-to-diameter ratio. Both low and high ratios are used,
with ratios varying between 0.3 and 3.0. The rotating cylinder 6.9 A versatile and convenient apparatus, consisting of a
can also be used as a mass loss coupon when the mass loss is kettle or flask (Fig. 1) of suitable size (usually 500 to
sufficiently large to be accurately measured using a conven- 5000 mL),inletandoutletportsfordeaeration,thermowelland
tional balance (with accuracy of 0.1 mg). temperature-regulating device, a heating device (mantle, hot
plate, or bath), and a specimen support system, should be used.
6.3 The RCE geometry may have an inner cylinder and an
The volume (of the solution) to surface area (of the specimen)
outer cylinder. The geometry is usually defined in terms of the
ratio has some effect on the corrosion rate and hence inhibitor
radiusoftheinnercylinderandtheradiusoftheoutercylinder.
efficiencies. A larger volume/surface area (minimum 40 mL/
When the outer diameter is several times the diameter of the
cm ) should be preferred.
innerelectrodethehydrodynamicsareessentiallycontrolledby
the diameter of the inner rotating cylinder (2). The outer 6.10 In some cases a wide-mouth jar with a suitable closure
cylinder may act as counter electrode. An RCE with only an can be used, but open-beaker tests should not be used because
inner cylinder may also be used. of evaporation and contamination. Do not conduct the open-
beaker test when H S (hydrogen sulfide) is used. In more
6.4 A saturated calomel electrode (SCE) with a controlled
complex tests, provisions might be needed for continuous flow
rate of leakage or a saturated calomel electrode utilizing a
or replenishment of the corrosive liquid, while simultaneously
semipermeable membrane or porous plug tip or silver/silver
maintaining a controlled atmosphere.
chloride or any other suitable electrode should be used as
reference electrode. The potential of the reference electrode 6.11 For experiments above atmospheric pressure, a high-
should be checked at periodic intervals to ensure the accuracy temperature, high-pressure rotating cylinder electrode (HTH-
of the electrode. For experiments at higher-temperature, a PRCE) system with an electrically isolated electrode system,
higher-pressure,referenceelectrodearrangementthatcanwith- an electrically isolated motor for rotating the electrode, and a
stand higher temperature and pressure should be used (22). vessel that can withstand high pressure without leakage should
This may require special care. be used.
6.5 Fig. 2 shows a typical rotating electrode unit.Arotating 6.12 A design of the vessel that can be used in elevated
shaft can be modified by drilling a hole in the shaft into which pressure conditions (23, 24) include a standard autoclave (Fig.
a polytetrafluoroethylene (PTFE) insulator is inserted. Inside 3) modified by lining on the inside with PTFE.The stirring rod
the PTFE insulator, a metal rod should be introduced (Fig. 2). can be modified by drilling a hole into that a PTFE insulator is
One end of the metal rod is threaded so that the cylindrical inserted. Inside the PTFE insulator, a metal rod is introduced.
G185−06
A. Reference Electrode
B. Inlet
C. Outlet
D. Luggin Capillary
E. Counter Electrode
F. Rotating Cylinder
G. Temperature Probe
H. pH Electrode
I. Rotating Cylinder Electrode or Coupon
FIG. 1Schematic of a RCE System (18)
G185−06
A. Outside View
B. Cross-Sectional View
FIG. 2Schematic Representation of a RCE with its Components (adapted from Ref 18)
Three O-rings are used to secure and to prevent leakage. One 7.3 Thespecimensarerinsedwithdistilledwater,degreased
end of the metal rod is threaded so that cylindrical (Fig. 3) by immersing in acetone (or any suitable alcohol), ultrasoni-
electrode can be attached. The other end of the rod, projecting cally cleaned for 1 minute, and dried. The surface of the
slightly above the motor unit, is attached directly the rotating specimens should not be touched with bare hands. The speci-
unit, through which the electrical connection is made. The rod mens are weighed to the nearest 0.1 mg (for mass loss
is rotated by a motor connected to the rod using a belt. The measurements), the dimensions are measured to the nearest 0.1
counter and reference electrodes are inserted inside the auto- mm, and the surface area is calculated.
clave.
7.4 Freshly prepared specimens are installed in the RCE
6.13 The suggested components can be modified, holder. If the test is not commenced within 4 h, the prepared
simplified, or made more sophisticated to fit the needs of a coupons shall be stored in a desiccator to avoid pre-rusting.
particular investigation.
8. Test Solutions
7. Materials
8.1 All solutions (oil and aqueous) should be obtained from
7.1 Methods for preparing specimens for tests and for the field for which the inhibitor is being evaluated. These are
removing specimens after the test are described in Practice G1. known as live solutions. It is important that live solutions do
Standardlaboratoryglasswareshouldbeusedforweighingand not already contain corrosion inhibitor. In the absence of live
measuring reagent volumes. solutions, synthetic solutions should be used, the composition
of which should be based on field water analysis. The compo-
7.2 The specimen shall be made of the material (such as,
sition of the solution should be determined and reported.
carbon steel) for which the inhibitor is being evaluated. The
Alternatively, standard brine (such as per Practice D1141)
specimen should have same metallographic structure as that
should be employed. The solutions should be prepared using
used in the service components. The specimens should be
analytical grade reagents and deionized water.
ground to a specified surface finish (such as, 150-grit). The
grinding should produce a reproducible surface finish, with no 8.2 The solutions should be deoxygenated by passing nitro-
rust deposits, pits, or deep scratches. All sharp edges on the gen or any other inert gas for sufficient time to reduce the
specimen should be ground. All loose dirt particles should be oxygen content below 5 ppb and preferably below 1 ppb in
removed. solution. The solution must be kept under deoxygenated
G185−06
1. Electrical Contact Unit
2. Techometer (Rotation Speed Display)
3. Rotation Controller
4. Electrochemical Instruments
5. Working Electrode
6. Reference Electrode
7. Water Cooler Coil
8. Gas Inlet
9. Thermocouple
10. Gas Outlet
11. Counter Electrode
12. Autoclave Body
13. Solution
14. PTFE Liner
FIG. 3Schematic Diagram of HTHPRCE System (20,21)
conditions. The oxygen concentration in solution depends on shall be kept as low as possible with guidelines of below 5 ppb
the quality of gases used to purge the solution. Any leaks
and preferably under 1 ppb oxygen in solution.
through vessel, tubing, and joints shall be avoided.
8.4 The solution pH before and after testing shall be
8.3 The appropriate composition of gases is determined by
measured, recorded, and reported. The solution pH should be
the composition of gases in the field for which the inhibitor is
monitored regularly (at least once a day) during the test.
evaluated. Hydrogen sulfide (H S) and carbon dioxide (CO )
2 2
8.5 Inhibi
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