1、Designation: G18 07 (Reapproved 2013)Standard Test Method forJoints, Fittings, and Patches in Coated Pipelines1This standard is issued under the fixed designation G18; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of las
2、t revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes determination of the com-parative corrosion preventative characteristics of materialsused for appl
3、ications to joints, couplings, irregular fittings, andpatched areas in coated pipelines. The test method is applicableto materials whose principal function is to act as barriersbetween the pipe surface and surrounding soil environment.1.2 The test method described employs measurements ofleakage curr
4、ent, capacitance, and dissipation factor to indicatechanges in the insulating effectiveness of joint and patchingmaterials.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of
5、 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.1.5 The values stated in SI units to three significant deci-mals ar
6、e to be regarded as the standard. The values given inparentheses are for information only.2. Referenced Documents2.1 ASTM Standards:2G12 Test Method for Nondestructive Measurement of FilmThickness of Pipeline Coatings on Steel3. Summary of Test Method3.1 The test method consists of an immersion test
7、 wherecoated pipe specimens, each containing a simulated joint, tee,or patched area, are suspended in an electrolyte and placedunder cathodic protection by connecting the specimens to thenegative () terminal of a 6-V d-c power supply (see Fig. 1).An anode, also immersed in the electrolyte and connec
8、ted tothe positive (+) terminal of the power supply, completes thetest circuit. Joint or patch performance is followed throughperiodic determinations of leakage current measured as voltagedrops across a calibrated resistor in the anode-to-cathodecircuit.3.2 Capacitance and dissipation factor measure
9、ments areused to supplement the periodic leakage current determina-tions.4. Significance and Use4.1 The exposed metal surfaces at joints, fittings, anddamaged areas in an otherwise coated pipeline will be sub-jected to corrosion if allowed to come in contact with the soilenvironment. The performance
10、 of joint and patching materialsdesigned to function as protective coverings will depend uponsuch factors as the ability of the material to bond to both thepipe coating and exposed metal surfaces, the integrity of themoisture seal at lapped joints, and the water absorptioncharacteristics of the join
11、t material.4.2 The existence of substantial leakage current through thecoating joint, patch, or fitting is reliable evidence that thematerial has suffered a significant decrease in its performanceas a protective barrier. In a similar manner, measured changesin joint capacitance and dissipation facto
12、r are useful becausethey are related to the water absorption rate of the jointmaterial. Water permeating an insulating barrier increases itscapacitance and its progress can be measured through the useof a suitable impedance bridge.5. Apparatus5.1 Test Vessel, nonconducting, shall be used to contain
13、thetest specimens. Dimensions of the vessel shall permit thefollowing requirements:5.1.1 The test vessel shall be large enough to allow forsuspension of the specimens in a vertical position and equidis-tant from a centrally located anode. The specimens shall nottouch either each other, the walls, or
14、 bottom of the test vessel.5.1.2 The test vessel shall be deep enough to allow forimmersion of the specimens in the electrolyte to the lower edgeof the upper moisture shield (see Fig. 2).1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Ap
15、plications and is the direct responsibility ofSubcommittee D01.48 on Durability of Pipeline Coating and Linings.Current edition approved June 1, 2013. Published June 2013. Originallyapproved in 1971. Last previous edition approved in 2007 as G18 07. DOI:10.1520/G0018-07R13.2For referenced ASTM stand
16、ards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
17、 19428-2959. United States1NOTE 1A commercially available, 42 L (11-gal) waste container ofhigh-density polyethylene can be conveniently used as a test vessel andwill accommodate up to six test specimens of a size indicated in 7.2.5.2 Support Plate, fabricated from a nonconductivematerial, to suspen
18、d the specimens in the test vessel. Thesupport plate shall contain an access hole for the referenceelectrode. A typical test cell is illustrated in Fig. 3.5.3 Anode, fabricated from 9.525 mm (0.375-in.) diameter300 series stainless steel rod, 609.6 mm (24.00 in.) long. Otherinert anodes such as carb
19、on or platinum may be used.5.4 D-C Voltmeter, to serve the dual purpose of (1)measuring leakage current as a potential drop across a 1,000-shunt in the measuring circuit and (2) measuring the potentialof the test specimen with reference to a Cu-CuSO4half cell.The instrument characteristics for these
20、 functions shall be:5.4.1 Voltage Range50 V full scale to 10 V full scale inoverlapping 1 and 3 ranges.5.4.2 Accuracy63 percent of full scale on all ranges.5.4.3 Input ResistanceGreater than 10 M on all ranges.5.5 Thickness GageMeasurements of coating thicknesswill be required for this test. Any ins
21、trument suitable for usewith Test Method G12 can be used. However, the choice ofmeasuring gage shall be compatible with the joint coatingthickness that will be encountered in the test.5.6 OhmmeterMeasurements for end-cap integrity shallbe made with a suitable ohmmeter capable of reading resis-tance
22、to an upper limit of 1000 M 65%.5.7 Reference ElectrodeA Cu-CuSO4half cell of conven-tional glass or plastic tube with porous plug construction, butpreferably not over 19.05 mm (34 in.) in diameter, having apotential of 0.316 V with respect to the standard hydrogenelectrode.NOTE 2A saturated calomel
23、 half cell may be used, but measurementsmade with it shall be converted to the Cu-CuSO4reference for reportingby adding 0.072 V to the observed reading.5.8 Voltage SourceA battery or rectifier-type power sup-ply shall be used to maintain a potential difference of 6.0 6 0.1V dc between each of the te
24、st specimens and the Cu-CuSO4half cell. Where multiple specimens are tested, a suitablevoltage-dividing circuit will be required for individual controlof the voltage applied to each specimen.5.9 Circuit Wiring from the anode to specimen shall be ofNo. 18 Awg insulated copper. A switch for disconnect
25、ing eachspecimen from its voltage source shall be included in thecircuit. A1000 61 percent, 1-W (minimum) precisionresistor shall be placed in the anode-to-cathode circuit as ashunt for current. A diagram illustrating the test cell wiringappears as Fig. 1.FIG. 1 Test CircuitsNOTE 1All dimensions are
26、 in millimetres with inches in parentheses.FIG. 2 Joint Test SpecimenFIG. 3 Joint Test CellG18 07 (2013)25.10 Capacitance BridgeMeasurements of specimen ca-pacitance and dissipation factor shall be made with a low-voltage a-c, resistive ratio arm-type bridge having the follow-ing characteristics:5.1
27、0.1 Oscillator Frequency, 1 kHz 62 % tolerance.5.10.2 Series Capacitance Range, 100 pF to 1100 pFaccuracy 61%61 pF, whichever is larger.5.10.3 Dissipation Factor Range, 0.002 to 1.0 at 1 kHzaccuracy 6 5%or6 0.001 dissipation, whichever is larger.5.11 ConnectorsMiniature, pin-type, insulated jacks sh
28、allbe used at the point of connection to each test specimen. Thejacks serve two important functions: (1) they permit thedisconnection of the specimen from the voltage source whenthe impedance bridge is in use, and (2) disconnection of thespecimen from the test circuit also removes the effect of stra
29、ycapacitance due to excessive lead length that may introduceerror into impedance bridge measurements.5.12 Foil ShieldAs an additional safeguard against straycapacitance effects, wrap the entire test vessel in heavy-gagealuminum foil as shown in Fig. 3 and ground the shield.6. Materials6.1 Electrolyt
30、eThe electrolyte shall consist of potable tapwater with the addition of 3 weight percent of technical-gradesodium chloride.6.2 Materials for sealing the ends of the specimens mayconsist of waxes, epoxies, or other suitable materials.However, they should have a dielectric constant in the rangefrom 2
31、to 6, and exhibit a low water-absorption rate. It is alsoimportant that the end-cap material maintains good adhesion toany coated pipe surfaces throughout the test period.7. Test Specimen7.1 The joint specimen shall be prepared from a represen-tative piece of 60.325 mm (2.375 in.) outside diameter,S
32、chedule 40, production-coated pipe.7.2 Each piece of coated pipe shall be 381 mm (15.0 in.)long and serve as a carrier for the particular joint material to betested.7.3 The simulated coating joint shall be made by cleaningaway a 101.6 mm (4.0-in.) band of pipe coating starting froma point 203.2 mm (
33、8.0 in.) below the upper end of the pipe. Thecoating may be removed by power brushing or any othersuitable device that will remove all of the coating in the areaindicated and leave a clean metal surface behind.7.4 The lower end of the test specimen shall be pluggedflush with a stopper and sealed or
34、capped with a materialmeeting the requirements of 6.2.7.5 When used, the primer shall be applied to the testspecimen in sufficient quantity to coat the test specimen froma point 88.9 mm (3.50 in.) below its upper end and ending ata point 317.5 mm (12.5 in.) from the upper end. This will allowfor a 1
35、2.7-mm (0.5-in.) band of excess primer beyond eachtape margin.7.6 The joint material to be tested shall be applied to theprepared pipe specimen (using a spiral wrap for tapes) andstarting from a point 101.6 mm (4.0 in.) below the upper endof the pipe section and ending at a point 304.8 mm (12.0 in.)
36、from the upper end. The 203.2 mm (8.0 in.) of joint materialthus applied should overlap the bared section of pipe by 50.8mm (2.0 in.) at each end. This distance represents the typicalcut-back distance encountered in the field joining, throughwelding, of coated pipe in 60.325 mm (2.375 in.) outsidedi
37、ameter size. A diagram of the joint specimen appears as Fig.2.7.7 The manner of applying the joint material shall be donein accordance with the manufacturers specifications. Thesupplier of the joint material should specify the desired timeinterval between the application of the material and the star
38、t ofthe test.NOTE 3Materials that are intended for use as a field-applied patchover damaged areas on coated pipelines can be tested using the sameprocedures, with the patching compound applied, instead, to the baredarea of the simulated joint.7.8 The upper 76.2 mm (3.0 in.) of the completed joint te
39、stspecimen shall be coated with the material used for the lowerend cap. This moisture shield can be conveniently made, in thecase of some waxes and epoxies, with several successive brushor dip-applied applications. The thickness of the moistureshield should be approximately 3.175 mm (0.125 in.).8. T
40、esting Temperature8.1 Perform all tests at a room temperature of 21 to 25C(70 to 77F).9. Preliminary Test Measurements9.1 Coating and Joint ThicknessMeasure and record thethickness of the base coating which lies exposed at each end ofthe test joint. Measurements shall be made in accordance withTest
41、Method G12. In a like manner, measure and record theaverage thickness of the joint covering.10. Procedure for Leakage Current Measurements10.1 Suspend the joint test specimens in the test vessel,observing the clearances specified in 5.1.1 and 5.1.2. Fill thevessel with electrolyte, bringing the flui
42、d level up to a pointmidway between the end cap and the lower edge of the jointmaterial.10.2 Connect one terminal of the ohmmeter to the testspecimen and the other terminal to the central anode. Theanode should be in contact with the electrolyte. Measure theapparent sample-to-anode resistance in ohm
43、s. The readingshall remain above 1000 M for 15 min. Readings below thisvalue probably indicates a faulty end-cap seal which should berepaired before the joint specimen is totally immersed.10.3 Totally immerse the joint test specimens up to thelower edge of the moisture shield. This level shall be ma
44、in-tained throughout the test period by regular additions of tapwater. The test shall be performed at room temperature.10.4 Connect each joint test specimen in series with a1000- 6 1 % (1-W) resistor, a suitable switch, and thenegative () terminal of the voltage source.G18 07 (2013)310.5 Connect the
45、 central stainless steel anode to the positive(+) terminal of the voltage source.10.6 Energize the voltage source.Adjust the voltage to eachspecimen by connecting a voltmeter between each sample andthe Cu-CuSO4half cell and varying the voltage output until 6.0V are measured between sample and half c
46、ell (see Fig. 1).10.7 As soon as the circuit is energized and voltage adjustedto each joint test specimen, measure and record the voltageacross each 1000- shunt resistor.10.8 Measure and record the closed circuit potential, EB,and open circuit potential, Eo, of each joint specimen withreference to t
47、he saturated Cu-CuSO4half cell.NOTE 4Any drop in closed circuit potential (EB) of a joint specimengreater than 20 % of the terminal voltage (Et) probably indicates adeveloping current leak in the joint area. In a like manner, any open circuitpotential (Eo) greater than 0.05 V may indicate the presen
48、ce of adeveloping conductive path across the test joint. (Both voltages arereferenced to the Cu-CuSO4half cell.)10.9 Using the d-c voltmeter in 5.4 measure and record thevoltage appearing across the terminals of the voltage supply.10.10 Continue, on a periodic basis, the measurementsspecified in 10.
49、7 through 10.9. Calculate the apparent jointresistance by the method described in 12.1.10.11 Prior to removal, reexamine a suspected joint failureto confirm that any observed drop in joint resistance is not dueto a faulty end-cap seal. This can best be accomplished byremoving the specimen from the test cell and allowing it to dry.When dry, reimmerse it to just above the level of the lower endcap and check the integrity of the cap by the method outlinedin Section 8.11. Procedure for Measurement of Capacitance andDissipation Factor11.1 The serie
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