ASTM G184-06
(Practice)Standard Practice for Evaluating and Qualifying Oil Field and Refinery Corrosion Inhibitors Using Rotating Cage
Standard Practice for Evaluating and Qualifying Oil Field and Refinery Corrosion Inhibitors Using Rotating Cage
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 it is important for a proper evaluation of inhibitors to test the inhibitors using a range of flow conditions.
The RC test system is relatively inexpensive and uses simple flat specimens that allow replicates to be run with each setup. (2-13).
In this practice, a general procedure is presented to obtain reproducible results using RC 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; however, 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 cage (RC) for evaluating corrosion inhibitors for oil field and refinery applications.
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:G184 −06
StandardPractice for
Evaluating and Qualifying Oil Field and Refinery Corrosion
Inhibitors Using Rotating Cage
This standard is issued under the fixed designation G184; 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 D4410 Terminology for Fluvial Sediment
1.1 This practice covers a generally accepted procedure to
3. Terminology
use the rotating cage (RC) for evaluating corrosion inhibitors
for oil field and refinery applications. 3.1 The terminology used throughout shall be in accordance
with Terminologies G15 and D4410 and Guide G170.
1.2 The values stated in SI units are to be regarded as
standard. The values given in parentheses are for information
4. Summary of Practice
only.
4.1 This practice provides a method of evaluating corrosion
1.3 This standard does not purport to address all of the
inhibitor efficiency in a RC apparatus. The method uses a
safety concerns, if any, associated with its use. It is the
well-defined rotating specimen setup and mass loss measure-
responsibility of the user of this standard to establish appro-
ments to determine corrosion rates in a laboratory apparatus.
priate safety and health practices and determine the applica-
Measurements are made at a number of rotation rates to
bility of regulatory limitations prior to use.
evaluate the inhibitor performance under increasingly severe
hydrodynamic conditions.
2. Referenced Documents
2.1 ASTM Standards:
5. Significance and Use
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
5.1 Selection of corrosion inhibitor for oil field and refinery
sion Test Specimens
applicationsinvolvesqualificationofcorrosioninhibitorsinthe
G15 Terminology Relating to Corrosion and CorrosionTest-
laboratory (see Guide G170). Field conditions should be
ing (Withdrawn 2010)
simulated in the laboratory in a fast and cost-effective manner
G16 Guide for Applying Statistics to Analysis of Corrosion
(1).
Data
G31 PracticeforLaboratoryImmersionCorrosionTestingof
5.2 Oil field corrosion inhibitors should provide protection
Metals
over a range of flow conditions from stagnant to that found
G46 Guide for Examination and Evaluation of Pitting Cor-
during typical production conditions. Not all inhibitors are
rosion
equallyeffectiveoverthisrangeofconditionssoitisimportant
G111 Guide for Corrosion Tests in High Temperature or
for a proper evaluation of inhibitors to test the inhibitors using
High Pressure Environment, or Both
a range of flow conditions.
G170 Guide for Evaluating and Qualifying Oilfield and
5.3 The RC test system is relatively inexpensive and uses
Refinery Corrosion Inhibitors in the Laboratory
simple flat specimens that allow replicates to be run with each
D1141 Practice for the Preparation of Substitute Ocean
setup. (2-13).
Water
5.4 In this practice, a general procedure is presented to
obtain reproducible results using RC to simulate the effects of
different types of coupon materials, inhibitor concentrations,
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
oil, gas and brine compositions, temperature, pressure, and
Corrosion Tests.
flow. Oil field fluids may often contain sand; however, this
Current edition approved Jan. 15, 2006. Published February 2006. DOI:
practice does not cover erosive effects that occur when sand is
10.1520/G0184-06.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or present.
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
G184−06
6. Apparatus
6.1 Fig. 1 shows the schematic diagram of the RC system.
An apparatus of suitable size (usually 7500 mL) is used,
consisting of inlet and outlet ports, thermowell, temperature-
regulating device, a heating device (mantle, hot plate, or bath),
and a specimen support system.
6.1.1 The vessel (typically 150-mm diameter) is manufac-
tured from an inert material. Cast acrylic and polytetrafluoro-
ethylene (PTFE) have been used.
6.1.2 A PTFE base is fitted at the bottom of the container.
At the center of the base, a hole is drilled into which the lower
end of a stirring rod is placed. This arrangement stabilizes the
stirrer and the coupons.
6.1.3 Typically, eight coupons (each of 75-mm length,
19-mm width, and 3-mm thickness, and a surface area of about
34.14 cm ) are supported between two PTFE disks (of 80-mm
diameter) mounted 75 mm apart on the stirring rod (Fig. 2).
Holes (10-mm diameter) about 15 mm away from the center
are drilled in the top and bottom PTFE plates of the cage to
increase the turbulence on the inside surface of the coupon
(Fig. 3). This experimental setup can be used at temperatures
up to 70°C and rotation speeds up to 1000 rpm.
NOTE 1—Gaps (typically 0.85 6 0.01 cm) between the coupons
introduce localized turbulence.
6.2 The flow pattern varies, depending on the rotation
FIG. 2Photo of Rotating Cage Containing Coupons
speed, the volume of the container, and the fluids. The flow
patterns are described in Guide G170.
FIG. 1Schematic Diagram of Rotating Cage
G184−06
7.4 Freshly prepared specimens are installed in the rotating
cage holder. If the test is not commenced within 4 h, the
prepared coupons shall be stored in a desiccator to avoid
pre-rusting.
8. Test Solutions
8.1 All solutions (oil and aqueous) should be obtained from
the field for which the inhibitor is being evaluated. These are
known as live solutions. It is important that live solutions do
not already contain corrosion inhibitor. In the absence of live
solutions, synthetic solutions should be used, the composition
of which should be based on field water analysis. The compo-
sition of the solution should be determined and reported.
Alternatively, standard brine (such as in Practice D1141)
should be employed. The solutions should be prepared using
NOTE 1—Holes (typically 1.0 cm in diameter, and about 1.5 cm from
the center) introduce localized turbulence. analytical grade reagents and deionized water.
FIG. 3Photo of Rotating Cage (Top View)
8.2 The solutions should be deoxygenated by passing nitro-
gen or any other inert gas for sufficient time to reduce the
oxygen content below 5 ppb and preferably below 1 ppb in
6.3 Volume of solution to the surface area of the specimen
solution. The solution must be kept under deoxygenated
hassomeeffectonthecorrosionrateandhenceontheinhibitor
conditions. The oxygen concentration in solution depends on
efficiencies. The minimum solution volume to metal surface
the quality of gases used to purge the solution. Any leaks
area is not less than 14 cm(11).
through the vessel, tubing, and joints shall be avoided.
6.4 Open-beaker tests should not be used because of evapo-
8.3 The appropriate composition of gases is determined by
ration and contamination. Open-beaker test must not be con-
the composition of gases in the field for which the inhibitor is
ducted when H S (hydrogen sulfide) is used. In some tests,
evaluated. (Warning—Hydrogen sulfide (H S) and carbon
provisions might be needed for continuous flow or replenish-
dioxide(CO )arecorrosivegases.)(Warning—H Sispoison-
2 2
ment of the corrosive liquid, while simultaneously maintaining
ous and should not be released into the atmosphere.) The
a controlled atmosphere.
appropriate composition of gas can be obtained by mixing H S
6.5 For experiments above atmospheric pressure, a high-
and CO streams from the standard laboratory gas supply.
temperature, high-pressure rotating cage (HTHPRC) system
Nitrogen or other inert gases can be used as a diluent to obtain
and a vessel that can withstand high pressure without leakage
the required composition of corrosive gases.Alternatively, gas
shall be used.
mixtures of the required compositions can be purchased from
suppliers of industrial gases. The concentrations of impurities,
6.6 The suggested components can be modified, simplified,
particularly oxygen, shall be kept as low as possible with
or made more sophisticated to fit the needs of a particular
guidelines of below 5 ppb and preferably under 1 ppb oxygen
investigation.
in solution.
7. Materials
8.4 The solution pH before and after testing shall be
7.1 Methods for preparing specimens for tests and for measured, recorded and reported. The solution pH should be
removing specimens after the test are described in Practice G1. monitored regularly (at least once a day) during the test.
Standardlaboratoryglasswareshouldbeusedforweighingand
8.5 Inhibitor concentrations should be measured and re-
measuring reagent volumes.
ported in % mass/volume or parts per million (ppm). The
7.2 The coupons shall be made of the material (such as method of injecting the inhibitor into the test solution should
carbon steel) for which the inhibitor is being evaluated. The reflect the actual field application. Water-soluble inhibitors
coupon should have the same metallographic structure as that may be injected neat (as-received) into the test solution
usedintheservicecomponents.Thecouponsshouldbeground (aqueous phase). To avoid the errors associated with handling
to a specified surface finish (such as 150-grit). The grinding small volumes of solution, an inhibitor stock solution may be
should produce a reproducible surface finish, with no rust preparedbydilutingtheas-receivedchemicalinanappropriate
deposits, pits, or deep scratches.All sharp edges on the coupon solvent. The type of solvent and the concentration of the stock
should be ground. All loose dirt particles should be removed. solution depend on the characteristics of the inhibitor and on
the specified test conditions.
7.3 The coupons are rinsed with distilled water, degreased
by immersing in acetone (or any suitable alcohol), ultrasoni- 8.6 Oil-soluble, water-dispersible inhibitor solutions are
cally cleaned for 1 min, and dried. The surface of the prepared by the following partition method. The required
specimens should not be touched with bare hands. The speci- amounts of oil and brine are placed in the partitioning vessel
mens are weighed to the nearest 0.1 mg, the dimensions are (usually a separation funnel). The relative volumes of oil and
measured to the nearest 0.1 mm, and the surface areas are aqueous phases should reflect the ratios of water and oil in the
calculated. field for which the inhibitor is evaluated. If samples from the
G184−06
field are not available, heptane, kerosine, or any suitable 9.10 The additional gas inlet on top of the vessel should
hydrocarbon may be used. The corrosion inhibitor is added to allow keeping the gas mixture blanket on top of the solution,
the oil phase. The vessel is vigorously shaken for 1 min to mix which is required when the experiment is planned for a longer
bothphasesthoroughly,andthephasesareallowedtoseparate. duration, for example, more than 24 h. Keep the gas flow rate
Heating to the temperature of the field helps in the separation. to a minimum. Take care that the gas does not entrain with the
The aqueous phase is removed and used as test solution. solution.
8.7 Oil-soluble inhibitors (usually as batch inhibitors) are
9.11 Use the speed controller to preset the rotation speed
dissolved in the oil phase to form an inhibited oil-phase. The
and to start the motor. The rotation speed usually stabilizes, as
coupons are exposed to this solution for a certain amount of
displayed by the tachometer, within 30 s. Alternatively the
time (usually 30 min). The coupons are then removed and
rotation speed can be set prior to pumping the solution into the
introduced into the experimental vessel.
vessel.
9. Experimental Procedure for Atmospheric Pressure
9.12 Terminate the experiment (typically after 24 h), and
Experiments
determine the corrosion rate from the amount of metal loss
(afterpropercleaningasdescribedinPracticeG1)asdescribed
9.1 A detailed procedure to determine corrosion rates from
in Practice G31. Examine and evaluate the samples for pitting
mass loss is described in Practice G31.
corrosion as in Guide G46. Calculate the average, standard
9.2 Solutions are usually prepared in a separate container
deviation, and coefficient of variation of the coupons corrosion
called the preparation vessel, pre-saturated with the required
rate for each run using the method presented in Guide G16.If
gas mixture, and preheated to the required temperature. (Pre-
pitting corrosion is observed, then the general corrosion rate
treatment described in Sections 8.4, 8.5, and 8.6 is usually
determined from mass loss could be invalid.
carried out in the preparation vessel.) Transfer solutions from
9.13 Determine inhibitor efficiency at each rotation speed
the preparation vessel to the experimental vessel (described in
and at each inhibitor concentration using the following equa-
Section6)underpositivenitrogenorotherinertgaspressureto
tion:
minimize air contamination during the transfer operation.
C.R 2 C.R
@ # @ #
9.3 Depending on the size of the experimental vessel,
No.inhibitor Inhibitor3100
Inhibitor Efficiency,% 5 (1)
@C.R#
heating unit (mantle, bath, or wrapper around the vessel),
No Inhibitor
difference between room, and experimental temperatures, a
where:
range of temperature may occur within the vessel.Take care to
[C.R] = the corrosion rate in absence of inhibitor,
No.inhibitor
avoid or minimize the temperature differentials. Heat the test
and
vessels slowly (usually at a rate of 0.1°C/s) to avoid overheat-
[C.R] = the corrosion rate in the presence of
inhibitor
ing. The exact protocol depends on the controller, the size and
inhibitor.
output of the heater, and parameters such as vessel size,
amount of liquid, thermal conductivity of liquid, and agitation.
10. Experimental Procedure for High-Temperature,
Maintain the test temperature within 2°C of the specified
High-Pressure Experiments
temperature.
10.1 Ageneralproceduretocarryoutcorrosionexperiments
9.4 Insert pre-weighed coupons (pretreated as necessary,
at elevated pressure and temperature is described in Guide
such as with batch inhibitors), thermometer, and pH probes (as
G11
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