1、Designation: G 185 06Standard Practice forEvaluating and Qualifying Oil Field and Refinery CorrosionInhibitors Using the Rotating Cylinder Electrode1This standard is issued under the fixed designation G 185; the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a generally accepted procedure touse the rotating cylinder
3、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 as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesa
4、fety 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:2D 1141 Practice for the Prepar
5、ation of Substitute OceanWaterD 4410 Terminology for Fluvial SedimentG1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making Potentiostatic andPotentiodyn
6、amic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and CorrosionTestingG16 Guide forApplying Statistics toAnalysis of CorrosionDataG31 Practice for Laboratory Immersion Corrosion Testingof MetalsG46 Guide for Examination and Evaluation of PittingCorrosionG59 Test Method for C
7、onducting Potentiodynamic Polar-ization Resistance MeasurementsG96 Guide for On-Line Monitoring of Corrosion in PlantEquipment (Electrical and Electrochemical Methods)G 102 Practice for Calculation of Corrosion Rates andRelated Information from Electrochemical MeasurementsG 106 Practice for Verifica
8、tion ofAlgorithm and Equipmentfor Electrochemical Impedance MeasurementsG 111 Guide for Corrosion Tests in High Temperature orHigh Pressure Environment, or BothG 170 Guide for Evaluating and Qualifying Oilfield andRefinery Corrosion Inhibitors in the Laboratory3. Terminology3.1 The terminology used
9、throughout shall be in accordancewith Terminologies G15and D 4410 and Guide G 170.4. 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-trochemical measure
10、ments 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 refineryapplications in
11、volves qualification of corrosion inhibitors in thelaboratory (see Guide G 170). Field conditions should besimulated in the laboratory in a fast and cost-effective manner(1).35.2 Oil field corrosion inhibitors should provide protectionover a range of flow conditions from stagnant to that foundduring
12、 typical production conditions. Not all inhibitors areequally effective over this range of conditions so that isimportant for a proper evaluation of inhibitors to test theinhibitors using a range of flow conditions.1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals
13、and is the direct responsibility of Subcommittee G01.05 on LaboratoryCorrosion Tests.Current edition approved Jan. 15, 2006. Published February 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStanda
14、rds volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5
15、.3 The RCE is a compact and relatively inexpensiveapproach to obtaining varying hydrodynamic 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 pr
16、actice, a general procedure is presented toobtain reproducible results using RCE to simulate 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 cov
17、er erosive effects that occur when sand is present.6. Apparatus6.1 Fig. 1 shows a schematic 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
18、62 rpm is typical. It is essential to be able to rotate theelectrode at both low and high 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
19、to theelectrodes are made by a brush contact. It is important for theconnection to be as 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 al
20、so be used as a mass loss coupon when the mass loss issufficiently large to be accurately 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
21、 and the radius of the outer cylinder.When the outer diameter is several times the diameter 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
22、 be used.6.4 A saturated calomel electrode (SCE) with a controlledrate of leakage or a 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 electr
23、odeshould be checked at periodic intervals to ensure the accuracyof the electrode. For 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
24、 rotating electrode unit. A rotatingshaft can be modified by drilling a hole in the shaft 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
25、 attached. The other end of the rod is attacheddirectly to the rotating unit, through which 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 monito
26、rthe location of the top of the rotating cylinder and rotating theshaft slowly through 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.Th
27、e assembly should also be rotated at its maximum rotationrate and the specimen wobble checked 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
28、. 2). The presence of gap betweenspecimen and holder will create crevice corrosion as well 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 expos
29、ed to the solution. The specimenholder is then attached to the rotating unit. Specimen, 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
30、 shaft is verticallypositioned. Even a very slight inclination could drasticallychange 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-regulat
31、ing device, a heating device (mantle, hotplate, or bath), and a specimen support system, 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 b
32、e preferred.6.10 In some cases a wide-mouth jar with a suitable closurecan be used, but 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 continuo
33、us flowor replenishment of the corrosive liquid, while simultaneouslymaintaining a controlled 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 iso
34、lated motor for rotating the electrode, and avessel that can withstand high pressure without 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
35、 be modified by drilling a hole into that a PTFE insulator isinserted. Inside the PTFE insulator, a metal rod is introduced.Three O-rings are used 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, pr
36、ojectingslightly above the motor unit, is attached directly the rotatingunit, through which the electrical connection is made. The rodG185062A. Reference ElectrodeB. InletC. OutletD. Luggin CapillaryE. Counter ElectrodeF. Rotating CylinderG. Temperature ProbeH. pH ElectrodeI. Rotating Cylinder Elect
37、rode or CouponFIG. 1 Schematic of a RCE System (18)G185063is rotated by 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, simpli-fied, or made more sophisticated to fit the needs of a parti
38、cularinvestigation.7. Materials7.1 Methods for preparing specimens for tests 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 ste
39、el) for which the inhibitor is being evaluated. Thespecimen should have same 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
40、, pits, or deep scratches. All sharp edges on thespecimen should be ground. 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 thespec
41、imens should not be touched with bare hands. The speci-mens are weighed to 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
42、within 4 h, the preparedcoupons shall be stored in a desiccator to avoid 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 c
43、ontain corrosion inhibitor. In the absence of livesolutions, synthetic solutions 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 D 1141)should be em
44、ployed. The solutions should be prepared usinganalytical grade reagents and 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 kep
45、t under deoxygenatedconditions. 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 determined bythe composition of gases in the field for which the in
46、hibitor 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 theA. Outside ViewB. Cross-Sectional ViewFIG. 2 Schematic Represe
47、ntation of a RCE with its Components (adapted from Ref 18)G185064standard 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 indus
48、trialgases. The concentrations of impurities, particularly oxygen,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 reg
49、ularly (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 the errors associated with handlingsmall volumes of solution, an inhibitor stock solution may beprepared by diluting the as-received chemical in an appropriatesolvent. The type of solvent and the concentration of the stocksoluti
