1、Designation: G 18 07Standard Test Method forJoints, Fittings, and Patches in Coated Pipelines1This standard is issued under the fixed designation G 18; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision.Anumb
2、er in parentheses indicates the year of last reapproval.Asuperscriptepsilon (e) 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 applications to joi
3、nts, 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 current, capacitanc
4、e, 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 thesafety conc
5、erns, 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 are to be regarde
6、d 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 wherecoated pi
7、pe 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 connected tothe posit
8、ive (+) 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 measurements areused t
9、o 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 of joint and p
10、atching 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 joint material.4.2
11、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 changes1This test method is under the jurisdiction of ASTM Commi
12、ttee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.48 on Durability of Pipeline Coating and Linings.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1971. Last previous edition approved in 1998 as G
13、18 88 (1998) which waswithdrawn March 2007 and reinstated in July 2007.2For referenced ASTM standards, 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 AST
14、M website.FIG. 1 Test Circuits1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.in joint capacitance and dissipation factor are useful becausethey are related to the water absorption rate of the jointmaterial. Water permeating an insul
15、ating 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 thetest specimens. Dimensions of the vessel shall permit thefollowing requirements:5.1.1 The test vessel shall be
16、 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 bottom of the test vessel.5.1.2 The test vessel shall be deep enough to allow forimmersion of the specimens in t
17、he electrolyte to the lower edgeof the upper moisture shield (see Fig. 2).NOTE 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, fab
18、ricated from a nonconductive mate-rial, to suspend the specimens in the test vessel. The supportplate shall contain an access hole for the reference electrode.Atypical 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
19、(24.00 in.) long. Otherinert anodes such as carbon 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-Vshunt in the measuring circuit and (2) measuring the potentialof the test specimen with reference to a Cu-CuSO4h
20、alf cell.The instrument characteristics for these functions shall be:5.4.1 Voltage Range50 V full scale to 10 V full scale inoverlapping 13 and 33 ranges.5.4.2 Accuracy63 percent of full scale on all ranges.5.4.3 Input ResistanceGreater than 10 MV on all ranges.5.5 Thickness GageMeasurements of coat
21、ing thicknesswill be required for this test. Any instrument suitable for usewith Test Method G12can 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
22、a suitable ohmmeter capable of reading resis-tance to an upper limit of 1000 MV65%.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 s
23、tandard hydrogenelectrode.NOTE 2A saturated calomel 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
24、 difference of 6.0 6 0.1V dc between each of the test 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 ofN
25、o. 18 Awg insulated copper. A switch for disconnecting eachspecimen from its voltage source shall be included in thecircuit. A1000 V61 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
26、 Fig. 1.5.10 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:NOTE 1All dimensions are in millimetres with inches in parentheses.FIG. 2 Joint Test SpecimenFIG. 3
27、Joint Test CellG180725.10.1 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-
28、type, insulated jacks shallbe 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 re
29、moves the effect of straycapacitance 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.
30、 Materials6.1 ElectrolyteThe 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. How-ever, they should have a dielectric co
31、nstant in the range from 2to 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 (2.3
32、75 in.) outside diameter,Schedule 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 start
33、ing froma point 203.2 mm (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 wit
34、h a stopper and sealed or 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 e
35、nd. This will allowfor a 12.7-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
36、 point 304.8 mm (12.0 in.)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 60.32
37、5 mm (2.375 in.) outsidediameter 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
38、 the material and the start 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.)
39、 of the completed joint testspecimen 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
40、 3.175 mm (0.125 in.).8. Testing 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 ma
41、de in accordance withTest 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 elec
42、trolyte, bringing the fluid 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-
43、to-anode resistance in ohms. The readingshall remain above 1000 MV 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 shi
44、eld. This level shall be main-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-V61 % (1-W) resistor, a suitable switch, and thenegative () terminal of the voltage source.10.5
45、 Connect the 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 sampl
46、e and half cell (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-V shunt resistor.G1807310.8 Measure and record the closed circuit potential, EB,and open circuit potential, Eo, of each joint specimen
47、 withreference to the 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
48、indicate the presence 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 measureme
49、ntsspecified in 10.7 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
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