1、Designation: G185 06 (Reapproved 2012)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 Potentiostatic andP
6、otentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G16 Guide for Applying Statistics to Analysis of CorrosionDataG31 Guide for Laboratory Immersion Corrosion Testing ofMetalsG46 Guide for Examination and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
7、Cor-rosionG59 Test 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 Measurem
8、entsG106 Practice for 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. Termino
9、logy3.1 The terminology 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
10、 or elec-trochemical 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
11、 and refineryapplications 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 s
12、tagnant to that foundduring 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 LaboratoryCorrosi
13、on Tests.Current edition approved Nov. 1, 2012. Published November 2012. Originallyapproved in 2006. Last previous edition approved in 2006 as G185 06. DOI:10.1520/G0185-06R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. Fo
14、r Annual Book 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.Copyr
15、ight ASTM International, 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 hydrody
16、namic conditions 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 sim
17、ulate the effects 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 schem
18、atic diagram 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 hi
19、gh speeds and 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 a
20、s noise free 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 accurate
21、ly measured 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 diam
22、eter of theinner 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
23、saturated calomel 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
24、experiments 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 sha
25、ft into whicha 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 w
26、hich the electricalconnection 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
27、one complete 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 c
28、hecked again 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 w
29、ell aschange 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,
30、 holder,and 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
31、the flow pattern.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
32、, should be 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
33、 open-beaker 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 cont
34、rolled atmosphere.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 wi
35、thout leakage 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
36、insulator, a metal rod is introduced.G185 06 (2012)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 (2012)3Three O-rings are used
37、to secure and 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
38、 a motor connected 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 te
39、sts and forremoving 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 s
40、ame metallographic 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 groun
41、d. All loose 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 t
42、o the nearest 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
43、pre-rusting.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 so
44、lutions should 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 an
45、d deionized 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 deoxygenatedA. Outside ViewB. Cross-Sectional ViewFIG. 2 Schematic
46、 Representation of a RCE with its Components (adapted from Ref 18)G185 06 (2012)4conditions. The oxygen concentration in solution depends onthe quality of gases used to purge the solution. Any leaksthrough vessel, tubing, and joints shall be avoided.8.3 The appropriate composition of gases is determ
47、ined bythe composition 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 thes
48、tandard laboratory 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,
49、shall be kept 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
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