1、Designation: G185 06 (Reapproved 2016)Standard Practice forEvaluating and Qualifying Oil Field and Refinery CorrosionInhibitors Using the Rotating Cylinder Electrode1This standard is issued under the fixed designation G185; the number immediately following the designation indicates the year oforigin
2、al adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a generally accepted procedure touse the rot
3、ating cylinder electrode (RCE) for evaluatingcorrosion inhibitors for oil field and refinery applications indefined flow conditions.1.2 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address a
4、ll of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1141 Practice for
5、the Preparation of Substitute OceanWaterD4410 Terminology for Fluvial SedimentG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making PotentiodynamicAnod
6、ic Polarization MeasurementsG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G16 Guide for Applying Statistics to Analysis of CorrosionDataG31 Guide for Laboratory Immersion Corrosion Testing ofMetalsG46 Guide for Examination and Evaluation of Pitting Cor-rosionG59 Test
7、Method for Conducting Potentiodynamic Polariza-tion Resistance MeasurementsG96 Guide for Online Monitoring of Corrosion in PlantEquipment (Electrical and Electrochemical Methods)G102 Practice for Calculation of Corrosion Rates and Re-lated Information from Electrochemical MeasurementsG106 Practice f
8、or Verification of Algorithm and Equipmentfor Electrochemical Impedance MeasurementsG111 Guide for Corrosion Tests in High Temperature orHigh Pressure Environment, or BothG170 Guide for Evaluating and Qualifying Oilfield andRefinery Corrosion Inhibitors in the Laboratory3. Terminology3.1 The termino
9、logy used throughout shall be in accordancewith Terminologies G15 and D4410 and Guide G170.4. Summary of Practice4.1 This practice provides a method of evaluating corrosioninhibitor efficiency in a RCE apparatus. The method uses awell-defined rotating specimen set up and mass loss or elec-trochemica
10、l measurements to determine corrosion rates in alaboratory apparatus. Measurements are made at a number ofrotating rates to evaluate the inhibitor performance underincreasingly severe hydrodynamic conditions.5. Significance and Use5.1 Selection of corrosion inhibitor for oil field and refineryapplic
11、ations involves qualification of corrosion inhibitors in thelaboratory (see Guide G170). Field conditions should besimulated in the laboratory in a fast and cost-effective manner(1).45.2 Oil field corrosion inhibitors should provide protectionover a range of flow conditions from stagnant to that fou
12、ndduring typical production conditions. Not all inhibitors areequally effective over this range of conditions so that is1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.05 on LaboratoryCorrosion Tests.Current ed
13、ition approved Nov. 1, 2016. Published November 2016. Originallyapproved in 2006. Last previous edition approved in 2012 as G185 06 (2012).DOI: 10.1520/G0185-06R16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Boo
14、k of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM In
15、ternational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1important for a proper evaluation of inhibitors to test theinhibitors using a range of flow conditions.5.3 The RCE is a compact and relatively inexpensiveapproach to obtaining varying hydrodynamic condit
16、ions in alaboratory apparatus. It allows electrochemical methods ofestimating corrosion rates on the specimen and produces auniform hydrodynamic state across the metal test surface.(2-21)5.4 In this practice, a general procedure is presented toobtain reproducible results using RCE to simulate the ef
17、fects ofdifferent types of coupon materials, inhibitor concentrations,oil, gas and brine compositions, temperature, pressure, andflow. Oil field fluids may often contain sand. This practice doesnot cover erosive effects that occur when sand is present.6. Apparatus6.1 Fig. 1 shows a schematic diagram
18、 of the RCE system.The RCE apparatus consists of a rotating unit driven by amotor that is attached to a sample holder.Asystem with a rangeof rotational speeds from 100 to 10 000 rpm with an accuracyof 62 rpm is typical. It is essential to be able to rotate theelectrode at both low and high speeds an
19、d to be able to measurethe speed and maintain it at a constant. The accuracy of therotation rate should be checked. At the side of the sampleholder where it is outside the cell, electrical connections to theelectrodes are made by a brush contact. It is important for theconnection to be as noise free
20、 as possible.6.2 The cylinder geometry is usually defined in terms of thelength-to-diameter ratio. Both low and high ratios are used,with ratios varying between 0.3 and 3.0. The rotating cylindercan also be used as a mass loss coupon when the mass loss issufficiently large to be accurately measured
21、using a conven-tional balance (with accuracy of 0.1 mg).6.3 The RCE geometry may have an inner cylinder and anouter cylinder. The geometry is usually defined in terms of theradius of the inner cylinder and the radius of the outer cylinder.When the outer diameter is several times the diameter of thei
22、nner electrode the hydrodynamics are essentially controlled bythe diameter of the inner rotating cylinder (2). The outercylinder may act as counter electrode. An RCE with only aninner cylinder may also be used.6.4 A saturated calomel electrode (SCE) with a controlledrate of leakage or a saturated ca
23、lomel electrode utilizing asemipermeable membrane or porous plug tip or silver/silverchloride or any other suitable electrode should be used asreference electrode. The potential of the reference electrodeshould be checked at periodic intervals to ensure the accuracyof the electrode. For experiments
24、at higher-temperature, ahigher-pressure, reference electrode arrangement that can with-stand higher temperature and pressure should be used (22).This may require special care.6.5 Fig. 2 shows a typical rotating electrode unit. A rotatingshaft can be modified by drilling a hole in the shaft into whic
25、ha polytetrafluoroethylene (PTFE) insulator is inserted. Insidethe PTFE insulator, a metal rod should be introduced (Fig. 2).One end of the metal rod is threaded so that the cylindricalelectrode can be attached. The other end of the rod is attacheddirectly to the rotating unit, through which the ele
26、ctricalconnection is made.6.6 After attaching the specimen to the shaft, the systemshould be checked for eccentricity and wobble. This can beaccomplished by installing a dial micrometer so as to monitorthe location of the top of the rotating cylinder and rotating theshaft slowly through one complete
27、 turn. The micrometershould then be moved to monitor the center of the specimen,and the process repeated. Finally the micrometer should bemoved to the bottom of the specimen and the process repeated.The assembly should also be rotated at its maximum rotationrate and the specimen wobble checked again
28、 using, forexample, a laser indicator or vibration monitor.6.7 Appropriate cylinder specimen (such as, carbon steel) ismachined and snugly fitted into the PTFE or any other suitablespecimen holder (Fig. 2). The presence of gap betweenspecimen and holder will create crevice corrosion as well aschange
29、 the flow pattern. If necessary, apply a very smallamount of epoxy to fit the specimen into the holder. Tightlyattach or screw an end-cap so that only the outer cylindricalarea of known length is exposed to the solution. The specimenholder is then attached to the rotating unit. Specimen, holder,and
30、end-cap should all have the same diameter.6.8 The rotating unit is attached into the experimentalvessel, ensuring that there is no leakage through the rotatingshaft and the holder and that the rotating shaft is verticallypositioned. Even a very slight inclination could drasticallychange the flow pat
31、tern.6.9 A versatile and convenient apparatus, consisting of akettle or flask (Fig. 1) of suitable size (usually 500 to5000 mL), inlet and outlet ports for deaeration, thermowell andtemperature-regulating device, a heating device (mantle, hotplate, or bath), and a specimen support system, should be
32、used.The volume (of the solution) to surface area (of the specimen)ratio has some effect on the corrosion rate and hence inhibitorefficiencies. A larger volume/surface area (minimum 40 mL/cm2) should be preferred.6.10 In some cases a wide-mouth jar with a suitable closurecan be used, but open-beaker
33、 tests should not be used becauseof evaporation and contamination. Do not conduct the open-beaker test when H2S (hydrogen sulfide) is used. In morecomplex tests, provisions might be needed for continuous flowor replenishment of the corrosive liquid, while simultaneouslymaintaining a controlled atmos
34、phere.6.11 For experiments above atmospheric pressure, a high-temperature, high-pressure rotating cylinder electrode (HTH-PRCE) system with an electrically isolated electrode system,an electrically isolated motor for rotating the electrode, and avessel that can withstand high pressure without leakag
35、e shouldbe used.6.12 A design of the vessel that can be used in elevatedpressure conditions (23, 24) include a standard autoclave (Fig.3) modified by lining on the inside with PTFE. The stirring rodcan be modified by drilling a hole into that a PTFE insulator isinserted. Inside the PTFE insulator, a
36、 metal rod is introduced.G185 06 (2016)2A. Reference ElectrodeB. InletC. OutletD. Luggin CapillaryE. Counter ElectrodeF. Rotating CylinderG. Temperature ProbeH. pH ElectrodeI. Rotating Cylinder Electrode or CouponFIG. 1 Schematic of a RCE System (18)G185 06 (2016)3Three O-rings are used to secure an
37、d to prevent leakage. Oneend of the metal rod is threaded so that cylindrical (Fig. 3)electrode can be attached. The other end of the rod, projectingslightly above the motor unit, is attached directly the rotatingunit, through which the electrical connection is made. The rodis rotated by a motor con
38、nected to the rod using a belt. Thecounter and reference electrodes are inserted inside the auto-clave.6.13 The suggested components can be modified,simplified, or made more sophisticated to fit the needs of aparticular investigation.7. Materials7.1 Methods for preparing specimens for tests and forr
39、emoving specimens after the test are described in Practice G1.Standard laboratory glassware should be used for weighing andmeasuring reagent volumes.7.2 The specimen shall be made of the material (such as,carbon steel) for which the inhibitor is being evaluated. Thespecimen should have same metallog
40、raphic structure as thatused in the service components. The specimens should beground to a specified surface finish (such as, 150-grit). Thegrinding should produce a reproducible surface finish, with norust deposits, pits, or deep scratches. All sharp edges on thespecimen should be ground. All loose
41、 dirt particles should beremoved.7.3 The specimens are rinsed with distilled water, degreasedby immersing in acetone (or any suitable alcohol), ultrasoni-cally cleaned for 1 minute, and dried. The surface of thespecimens should not be touched with bare hands. The speci-mens are weighed to the neares
42、t 0.1 mg (for mass lossmeasurements), the dimensions are measured to the nearest 0.1mm, and the surface area is calculated.7.4 Freshly prepared specimens are installed in the RCEholder. If the test is not commenced within 4 h, the preparedcoupons shall be stored in a desiccator to avoid pre-rusting.
43、8. Test Solutions8.1 All solutions (oil and aqueous) should be obtained fromthe field for which the inhibitor is being evaluated. These areknown as live solutions. It is important that live solutions donot already contain corrosion inhibitor. In the absence of livesolutions, synthetic solutions shou
44、ld be used, the compositionof which should be based on field water analysis. The compo-sition of the solution should be determined and reported.Alternatively, standard brine (such as per Practice D1141)should be employed. The solutions should be prepared usinganalytical grade reagents and deionized
45、water.8.2 The solutions should be deoxygenated by passing nitro-gen or any other inert gas for sufficient time to reduce theoxygen content below 5 ppb and preferably below 1 ppb insolution. The solution must be kept under deoxygenatedconditions. The oxygen concentration in solution depends onthe qua
46、lity of gases used to purge the solution. Any leaksthrough vessel, tubing, and joints shall be avoided.A. Outside ViewB. Cross-Sectional ViewFIG. 2 Schematic Representation of a RCE with its Components (adapted from Ref 18)G185 06 (2016)48.3 The appropriate composition of gases is determined bythe c
47、omposition of gases in the field for which the inhibitor isevaluated. Hydrogen sulfide (H2S) and carbon dioxide (CO2)are corrosive gases. H2S is poisonous and should not bereleased to the atmosphere. The appropriate composition of gascan be obtained by mixing H2S and CO2streams from thestandard labo
48、ratory gas supply. Nitrogen or other inert gasescan be used as a diluent to obtain the required ratios of thecorrosive gases. Alternatively, gas mixtures of the requiredcompositions can be purchased from suppliers of industrialgases. The concentrations of impurities, particularly oxygen,shall be kep
49、t as low as possible with guidelines of below 5 ppband preferably under 1 ppb oxygen in solution.8.4 The solution pH before and after testing shall bemeasured, recorded, and reported. The solution pH should bemonitored regularly (at least once a day) during the test.8.5 Inhibitor concentrations should be measured and re-ported in % mass/volume or parts per million (ppm). Themethod of injecting the inhibitor into the test solution shouldreflect the actual field application. Water-soluble inhibitorsmay be injected neat (as-received) into the test solution(aqueous phase). To avoid
