1、Designation:G907Standard Test Method forWater Penetration into Pipeline Coatings1This standard is issued under the fixed designation G 9; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A number in parent
2、heses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This method covers the determination of the apparentrate of depth of water penetration into insulating coatingsapplied to pipe.1.2 The values stated i
3、n 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 thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and he
4、alth practices and determine the applica-bility of regulatory limitations prior to use.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 method consists of an immersion-type test wh
5、erepipe specimens are suspended in an aqueous electrolyte for theduration of the test period. Electrical measurements of coatingcapacitance and dissipation factor are used to follow the waterabsorption rate of the test materials.4. Significance and Use4.1 The deterioration of an insulating coating f
6、ilm is inti-mately related to its moisture content. The water penetrationtest provides a means for monitoring the passage of moisturethrough a coating material by means of changes in its dielectricconstant. When expressed in relation to time, the test data willreflect a rate of deterioration which i
7、s a characteristic of thecoating material and will bear a relation to its expected usefullife as an insulating coating. The test for water penetration willalso provide information that is useful in establishing theoptimum coating thickness for a given material.5. Apparatus5.1 Immersion CellAny suita
8、ble nonmetallic vessel tocontain the test specimens. Dimensions of the vessel shallpermit the following requirements:5.1.1 Test specimens shall be suspended vertically with atleast 25 mm (1.0 in.) clearance from the sides and bottom.5.1.2 Test specimens shall be separated by not less than 25to 40 mm
9、 (1 to 1.5 in.) and a vertically suspended anode shallbe placed at an equal distance from each specimen not less thanthe separation of distance.5.1.3 The test vessel shall be deep enough to allow forimmersion of the samples in the electrolyte to the levelspecified in 8.1.NOTE 1Commercially available
10、, glass battery jars in 2-dm3(0.55-gal)and 10-dm3(2.7-gal) sizes can be conveniently used with 19-mm(0.75-in.) and 51-mm (2.0-in. nominal) diameter specimens, respectively.5.1.4 A suitable sample support plate fabricated from amaterial having a low dielectric constant shall be used tosuspend the sam
11、ples and anode above the immersion cell. Thesupport plate shall contain an access hole for the referenceelectrode. A typical test cell is illustrated in Fig. 1.5.2 Electrolyte, consisting of tap water with the addition of1 weight % of each of the following technical-grade anhydroussalts: sodium chlo
12、ride, sodium sulfate, and sodium carbonate.NOTE 2Add 30 g (1.05 oz) of sodium chloride for each dm3(0.26 gal)of water.5.2.1 The electrolyte in the immersion cell shall be main-tained at the proper level by regular additions of tap water. Theelectrolyte shall not be reused after completion of the tes
13、t.5.3 Voltage SourceA direct current power supply, capableof supplying low ripple voltage shall be used to maintain apotential difference of 6.0 6 0.1 V dc between each of the testspecimens and a common electrode.5.4 ConnectorsWiring connections from the anode to thespecimen shall be of No. 18 AWG i
14、nsulated copper. Attach-ment to the anode shall be sealed and kept above the level ofthe electrolyte. Attachment to the specimen shall be made by a1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibil
15、ity ofSubcommittee D01.48 on Durability of Pipeline Coating and Linings.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1969. Last previous edition approved in 1998 as G987(1998) which waswithdrawn March 2007 and reinstated in July 2007.2For referenced ASTM standard
16、s, 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1
17、9428-2959, United States.method that will allow disconnection from the anode when themeasuring bridge is in use. A convenient means for accom-plishing this is through the use of insulated pin-type jacks.5.5 Capacitance Bridge3,4Measurements of equivalentspecimen capacitance and coating dissipation f
18、actor shall bemade with a low-voltage a-c, resistive-ratio-arm type measur-ing bridge having the following characteristics:5.5.1 Oscillator frequency, 1 kHz 6 2%,5.5.2 Series capacitance range, 1 to 1100 pF 6 1%,5.5.3 Series capacitance sensitivity, 0.5 pF,5.5.4 Dissipation factor range, 0.001 to 1.
19、0 at 1 kHz, and5.5.5 Dissipation factor sensitivity, 0.001 at 1 kHz.5.6 Measuring CircuitMeasurements of specimen capaci-tance and coating dissipation factor shall be made using acircuit that places the sample unknown in series with thecomparison circuit of the measuring bridge. Connection of theunk
20、nown to the measuring bridge shall be made in such amanner as to eliminate the introduction of stray capacitanceinto the measuring circuit. A diagram for connecting the testcell to the bridge is shown in Fig. 2. In this arrangement, boththe test leads are shielded and the chassis of the bridge isgro
21、unded. The immersion cell shall also be shielded to avoidcapacitance effects from surrounding objects.NOTE 3A shield for the test cell can conveniently be fabricated frommost commercially-available tin or aluminum foils of approximately0.0382-mm (0.0015-in.) thickness and formed around the container
22、.5.7 Thickness GageMeasurements of coating thicknesswill be required for this test. Any instrument suitable for usewith Test Method G12can be used.5.8 Anode, fabricated from 4.76-mm (0.1875-in.) diameterAISI Type 303 stainless-steel rod, and shall be 178 mm (7.00in.) long, with the upper 50 mm (2.00
23、 in.) threaded to accept alocking nut.6. Test Specimen6.1 The test specimen shall be a representative piece ofproduction-coated pipe and shall be free of obvious coatingflaws or defects (see Fig. 3). Any suitable diameter andspecimen length can be used. Physical limitations of theimmersion cells sug
24、gested in 5.1.3, Note 1, make it necessaryto restrict the overall sample length to approximately 300 mm(12.0 in.) for both the 26.7-mm (0.75-in. nominal) and60.3-mm (2.0-in. nominal) diameter coated pipe specimens.6.2 The upper and lower ends of the test specimen shall beplugged and sealed with nonc
25、onductive caps of sufficient bulkto minimize effectively capacitive end effects in the measuringcircuit. For this purpose, an end-cap thickness of from 13 mm(0.5 in.) to 19 mm (0.75 in.) shall be maintained.6.2.1 The end-cap material shall have a dielectric constantin the range from 2 to 6, bond wel
26、l to the coating surface, andexhibit a low water-absorption rate. Several commerciallyavailable poly(vinyl chloride)-paraffin compounds,5,4are wellsuited for this purpose. They have a melting point in the 150 to200C (300 to 390F) range, can be poured into molds aroundthe pipe sample, and appear as r
27、esilient, durable solids at roomtemperature.NOTE 4Using these materials, the end-caps can be applied to therequired thickness by repeated dipping of the sample ends into amolten-wax bath, or through the use of light-weight, disposable molds ofaluminum foil or paper formed around the pipe sample to a
28、llow the castingof the caps directly to the surface of the coated pipe sample.6.3 The end of the specimen which will protrude above theimmersion line shall be provided with a suitable means ofsupport and a separate wire connection for electrical purposes.The protruding end of the sample shall be wat
29、erproofed with athin coating of end-cap material (see Fig. 1).7. Preliminary Test Measurements7.1 Coating ThicknessMeasure and record the coatingthickness by referring to Test Method G12.7.2 Specimen LengthMeasure and record the length ofexposed coating surface, between the end caps.7.3 End-Cap Capa
30、citanceVertically suspend the testspecimens and anode in the immersion cell, observing theclearances specified in 5.1.1 through 5.1.3. Fill the containerwith the electrolyte until it just covers the lower end cap.3The sole source of supply of the General Model 1656 Impedance Bridge knownto the commi
31、ttee at this time is GenRad, Concord, MA 01742.4If you are aware of alternative suppliers, please provide this information toASTM Headquarters.Your comments will receive careful consideration at a meetingof the responsible technical committee,1which you may attend.5The sole source of supply of the B
32、oler Petroleum No. L-480-86 Wax Blendknown to the committee at this time is Boler Petroleum Co. 85 Old Eagle SchoolRd., Wayne, PA 19087.FIG. 1 Typical Test CellG9072Energize the impedance bridge and measure the series capaci-tance, Ccof the lower end cap.7.4 Initial Coating CapacitanceAdd additional
33、 electro-lyte to the immersion cell until its level reaches the lower edgeof the upper end cap. Immediately measure and record theinitial series capacitance, C0, and dissipation factor, DF,ofthespecimen.8. Procedure8.1 Energize each specimen by connecting it to the negativeside of the voltage source
34、. Keep each sample energized andimmersed to the lower edge of the upper end cap for theduration of the test period. Maintain the specified electrolytelevel through regular additions of tap water.8.2 Throughout the test make periodic measurements of theseries capacitance and dissipation factor of the
35、 immersedspecimens in the following manner:8.2.1 Temporarily disconnect the test specimen from thevoltage source. Verify that the electrolyte is at the proper levelwithin the immersion cell. Connect the measuring bridgebetween the test specimen and stainless-steel anode. Energizethe bridge and measu
36、re the series capacitance, C, and dissipa-tion faction, DF, of the test specimen.8.2.2 Using the observed value of series capacitance, Cs,calculate the apparent depth of water penetration by the methoddescribed in 9.2.8.2.3 Repeat the measurements of series capacitance andspecimen dissipation factor
37、 at periodic intervals throughout theduration of the test. The frequency of measurement will dependupon the rate of deterioration of the coating sample. Where thewater penetration process is relatively rapid, daily readings ofsample capacitance and dissipation factor will be required.Normally, readi
38、ngs made at weekly intervals will adequatelydefine the penetration rate.NOTE 5Some coatings exhibit an initial rise in capacitance anddissipation factor, but reach a state of equilibrium in 6 to 9 months. Anincrease in capacitance and dissipation factor following this period ofequilibrium, (or failu
39、re to reach equilibrium) indicates impending failure.A sample can be considered to have failed when the dissipation factorreaches a value of 1.0.FIG. 2 Connecting the Test Cell to the BridgeNOTE 1Dimensions are in millimetres with inches in parentheses.FIG. 3 Detail Drawing of Pipe SpecimenG90739. C
40、alculations9.1 Dielectric ConstantCalculate the dielectric constant,K0, for the coating film as follows:K05C02 Cc! ln 2t01 d!/dNL(1)where:K0= dielectric constant,C0= initial coating capacitance, pF,Cc= end-cap capacitance, pF,d = outside pipe diameter, mm (in.),t0= initial coating thickness, mm (in.
41、),L = exposed coating length, mm (in.), andN = 0.0556 when d, t0, L, are in mm (1.413 when d, t0,L,are in in.).9.2 Apparent Depth of PenetrationCalculate the depth ofwater penetration by applying the calculated value of K0from9.1 and the measured value of equivalent series capacitance, C,to the foll
42、owing equations:tp5 t02 t (2)t 5 d/2!eM! 2 1where:M = NK0L/(C Cc),t = unpenetrated coating thickness, mm (in.),C = series capacitance, pF, andtp= depth of penetration, mm (in.).10. Report10.1 The report shall include the following:10.1.1 Complete identification of specimen, including:10.1.1.1 Name a
43、nd code number of the coating,10.1.1.2 Size of pipe,10.1.1.3 Source, production date, and production-run num-ber,10.1.1.4 Minimum, maximum, and average coating thick-ness,10.1.1.5 Dates of starting and terminating test, and10.1.1.6 Other information that may be pertinent,10.1.2 Magnitude and polarit
44、y of d-c voltage applied tosample during the test period,10.1.3 Length of the test period in days,10.1.4 Apparent depth of water penetration for the testperiod indicated,10.1.5 Initial value of coating dissipation factor, and10.1.6 Value of coating dissipation factor at the end of thetest period.NOT
45、E 6For the purpose of monitoring coating performance, plottedgraphs of apparent depth of water penetration versus time in rectangularcoordinates and coating dissipation factor versus time in semilogarithmiccoordinates will render useful information over the duration of the testperiod.11. Precision a
46、nd Bias11.1 Due to the range of coating formulations, thicknesses,densities, etc., found among commercially available coatedpipe samples, the reproducibility of the test results by thesemethods will tend to be poorer than those expected oninsulating material of a more uniform nature.11.2 The precisi
47、on (reproducibility)6of the dissipation fac-tor and depth of penetration by these methods in general isconsidered to be such that when two tests are performedconsecutively on the same specimen under identical condi-tions, the difference between the two results may normally beexpected not to exceed 6
48、 5 % of their mean.12. Keywords12.1 capacitance; coating; dielectric constant; dissipationfactor; immersion; pipeline; water absorption; waterpenetrationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. U
49、sers of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideratio
