1、Designation: F2660 13Standard Test Method forQualifying Coatings for Use on A490 Structural BoltsRelative to Environmental Hydrogen Embrittlement1This standard is issued under the fixed designation F2660; the number immediately following the designation indicates the year oforiginal adoption or, in
2、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 test method defines the procedures and tests toevaluate the effect of a coating
3、 system on the susceptibility toenvironmental hydrogen embrittlement (EHE) of an ASTMA490 high strength structural bolt.1.2 This test method shall qualify a coating system for usewith any size of A490 bolts (that is,12 to 1-12 in.) high strengthstructural bolts, relative to EHE.1.3 The characteristi
4、c to be evaluated by this test method isthe susceptibility to EHE caused by hydrogen generated fromcorrosion protection of the steel bolt by sacrificial galvaniccorrosion of the coating. Testing shall be performed on coated,specimen ASTM A490 bolts manufactured to the maximumsusceptible tensile stre
5、ngth values (see Table 1) of the bolt (seeSection 5 Specimen Bolt Requirements). The internal hydro-gen embrittlement (IHE) susceptibility will also be inherentlyevaluated when the EHE is tested through this test method.There is no need for a separate IHE susceptibility test.1.4 The values stated in
6、 inch-pound units are to be regardedas standard. No other units of measurement are included in thisstandard.1.5 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
7、and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A490 Specification for Structural Bolts, Alloy Steel, HeatTreated, 150 ksi Minimum Tensile StrengthE4 Practices for Force Verification of Testing MachinesE8/E8M Tes
8、t Methods for Tension Testing of Metallic Ma-terialsF519 Test Method for Mechanical Hydrogen EmbrittlementEvaluation of Plating/Coating Processes and Service En-vironmentsF606 Test Methods for Determining the Mechanical Proper-ties of Externally and Internally Threaded Fasteners,Washers, Direct Tens
9、ion Indicators, and RivetsF1624 Test Method for Measurement of Hydrogen Em-brittlement Threshold in Steel by the Incremental StepLoading TechniqueF1789 Terminology for F16 Mechanical FastenersF2078 Terminology Relating to Hydrogen EmbrittlementTestingG3 Practice for Conventions Applicable to Electro
10、chemicalMeasurements in Corrosion TestingG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G44 Practice for Exposure of Metals andAlloys byAlternateImmersion in Neutral 3.5 % Sodium Chloride SolutionG82 Guide for Development and Use of a Galvanic Seriesfor Predicting Galv
11、anic Corrosion Performance2.2 Research Council on Structural Connections:Specification for Structural Joints Using High Strength Bolts(LRFD) Load and Resistance Factor DesignSpecification for Structural Joints Using High Strength Bolts(ASD) Allowable Stress Design2.3 Other References:Townsend Jr., H
12、. E., Met Trans, V6A, April, 1976Raymond, L., The Susceptibility of Fasteners to HydrogenEmbrittlement and Stress Corrosion Cracking: FastenerSystem Design. In J. H. Bickford, therefore, thespecimen bolts shall not have standard A490 markings so theywill not be identified as standard A490 bolts.5.1.
13、2 Specimen bolts shall be one of two nominal inch sizes:3/4-10 UNC or 1-8 UNC. Alternatively, small specimen sizebolts, 1/2-13 UNC may be used, but are subject to more severestrength requirements shown in 8.4.5.1.3 Specimen bolts shall for a lot that displays themaximum wedge tensile load condition
14、permitted by Specifi-cation A490, when tested in accordance with Test MethodsF606. Table 1 gives the range of acceptable wedge tensile loadsfor each specimen bolt size.5.1.4 Test results shall be provided by an ISO 17025accredited laboratory. Wedge tensile strengths for the specimenbolts must be wit
15、hin the range specified in Table 1 anddimensional and compositional conformance to SpecificationA490 shall be provided by the supplier of each specimen lot.5.2 Coatings:5.2.1 The coating to be evaluated shall be applied to allspecimen bolts under normal production conditions.5.2.2 The process of coa
16、ting specimen bolts shall include allpost-coating processing under normal production conditions.5.3 Uncoated Bolts:5.3.1 Testing shall be carried out using ASTM A490 Type 1bolts produced at the same time with the same processes andfrom the same lot of steel alloy as coated bolts.6. Sample Quantities
17、 Required6.1 A minimum of fifteen (15) bolts from any specimen lotshall be used for evaluation and qualification. Ten (10) boltsshall be coated and the remaining five (5) bolts shall remainuncoated. Additional samples may be required for repeat testand shall be held in contingency.7. Test Procedures
18、7.1 Open Circuit Potential (OCP):7.1.1 The freely corroding or Open Circuit Potential (OCP)shall be measured in 3.5% NaCl solution produced in accor-dance with Practice G44 to characterize the galvanic corrosionbehavior of the coating relative to the steel bolt. The OCPmeasurement shall be made on a
19、 coated specimen bolt inaccordance with Practice G3. The OCP measurement shall betaken using a potentiostat capable of making measurementswith a resolution no less than 6 5mV.NOTE 1If the coating is a known material then the measured OCP canbe compared to the values described in Guide G82.7.1.2 A se
20、cond OCP test shall be performed and the twotests shall be compared for consistency. If the OCP test is not6 5 mV with a known value for a known coating or with theother OCP test for an unknown coating, then a known materialother than the coating shall be used to test the accuracy of thereference el
21、ectrode. If the electrode is accurate, then anotherbolt sample shall be tested to obtain consistency. Some reasonsfor inconsistency include dissimilar materials in the test setupor coating voids that can change the OCP value.7.2 Environmental Hydrogen Embrittlement Testing:7.2.1 Mechanical Test Set-
22、up:7.2.1.1 The test shall be conducted on bolts that have beentruncated by removal of the bolt head. Cut off the bolt headusing a water cooled cut off saw or other device that does notcause excessive heating of the bolt. The length of the specimenbolt for testing shall be a minimum length of 1.5 inc
23、hes and amaximum length of 4.0 inches. The truncated bolt specimenshall be adjusted to achieve the placement of a minimum oftwo threads between the gripping devices. The exposed threadsshall be equally spaced on each side of the minor diameter ofthe threads. This placement of the bolt specimen in th
24、e grippingdevice is shown in Fig. 1.7.2.1.2 The loading method required for this test is four-point (4 pt) bend, which produces constant moment along thegage section so that the stress may be calculated anywherealong the length of the fastener. The test is conducted underdisplacement control. The lo
25、ading method shall have a speci-fied load accuracy of 6 0.5%, programmable to increaseTABLE 1 Specimen Bolt Sizes and Wedge Tensile Load ValuesNominalSizeMinimumLengthTensileStressAreaWedge TensileLoad(D) (in.)As(in.2)Min.(lb)Max.(lb)1/2-13 1-1/2 0.1419 25,600 27,6003/4-10 2-1/2 0.3345 59,000 63,000
26、1-8 5 0.6057 103,000 107,000F2660 132incrementally in steps of load and time. The loading methodshall be within the guidelines of calibration, force range,resolution, and verification of Practices E4.7.2.2 Fast Fracture Testing:7.2.2.1 The first step in the testing sequence shall be ameasurement of
27、the fast fracture load of the specimen bolts inbending. Determine this value by performing a test in accor-dance with Test Method F1624, Section 8, as shown in Fig. 2A,using a fast fracture protocol. Test a minimum of five uncoatedspecimen bolts and a minimum of five coated specimen bolts.The averag
28、e of these five test results shall determine the fastfracture strength of each condition.7.2.2.2 The average fast fracture strength in bending ofcoated bolts, FFS(B)coatedmust be within 6 5% of the averagefast fracture strength for uncoated bolts, FFS(B)uncoated.Ifthecoated bolts exhibit a fast frac
29、ture strength that is below 95%FIG. 1 Four-Point Bend Loading of Fasteners. Maximum Tensile Stress, t= 32Pb/d3FIG. 2F2660 133of the fast fracture strength for uncoated bolts, the coating isdisqualified from this test.NOTE 2Lower than 95% fast fracture strength for the coated samplesis an indication
30、that the coating process may have affected the strength ofthe specimen bolts.7.2.3 EHE Sample Testing:7.2.3.1 To measure the EHE susceptibility of the fastener/coating system, bolts are tested in the environment/setupdescribed in section 7.1.1 and 7.2.3.3 using the step loadmethodology described in
31、Test Method F1624, Section 8, tomeasure Pth.7.2.3.2 A galvanic condition (see Annex A1) is created byinscribing a mark in the coating at the root of a bolt thread toexpose the steel substrate. This condition simulates a damagedcoating, also referred to as “coating holiday.” The scribe markin the coa
32、ting shall be located between the exposed threads (seeFig. 1) between the gripping devices and shall have a length ofat least one diameter and a width that exposes the thread root.Care must be taken not to cause any damage in the form of anotch to the bolt itself. To this end an abrasive medium, low
33、erin hardness than the bolt material is recommended.NOTE 3For example, a wire can be placed at the base of the exposedthread in scribing the coating circumferentially to a length of onediameter.7.2.3.3 To test at the OCP of the coating, the environmentalchamber shall be partially filled with 3.5% Na
34、Cl solutionproduced in accordance with Practice G44 with the level of thesolution being maintained below the threshold section of thebolt specimen. The reference electrode shall be placed in closevicinity to the scribe mark. An electrochemical potential equalto the measured OCP from section 7.1 shal
35、l be imposed on thespecimen during the test to negate the influence of anydissimilar metals in the environmental chamber, such as theloading pins and gripping devices. When the potential readingis stable, the remaining salt solution is added to the chamber tofully immerse the bolt sample.(1) As an a
36、lternative to imposing an electrochemicalpotential, the test can be performed under freely corrodingconditions, provided the coated specimen is isolated from allmetal contacts. It should be verified that there is no conduc-tivity between the specimen and the adapters. The freelycorroding potential,
37、or OCP (section 7.1), shall be measuredand recorded.7.2.3.4 The loading profile of the first coated sample boltshall be (10/5/2,4), or ten (10) steps tested with a hold time of2-hours followed by ten (10) steps at a hold time of 4-hours in5% increments of FFS(B)coated, taken as the initial value ofP
38、max. Loading is not released during the transition from the2-hour to 4-hour hold requirement. The test proceeds until thesample experiences a load drop of more than 5% during anysingle step in the load rate. An example of the step loadingprofile is shown in Fig. 2B.7.2.3.5 Subsequent tests shall be
39、at progressively decreasingloading rates by using the same (10/5/2,4) profile and loweringPmaxto the value of the previous threshold load therebylowering the Pfor each loading step.As Pmaxis decreased, theresolution is increased and the loading rate is decreased. Thetest proceeds until the sample ex
40、periences a load drop of morethan 5% during any single step in the load rate.7.2.3.6 The threshold load for the coated bolts, Pth,isobtained when the threshold load for the subsequent test iswithin a value of 5% of Pmaxof the threshold load measured onthe previous test at the higher loading rate. Th
41、e minimum valueof the threshold load obtained through these measurementsshall be used in the calculation described in Section 8. Thelowest threshold value established by consecutive tests shall beconsidered the threshold load for the coated bolts, Pth. Theminimum number of samples to accomplish the
42、establishmentof the threshold load shall be five (5) coated specimen bolts.8. EHE Acceptance Criterion for Coated ASTM A490Bolts8.1 Perform tests on fasteners to the same hydrogen em-brittlement acceptance criterion as the Test Method F519, Type1a specimens that require a threshold stress equal in v
43、alue tothat of 75% of the notch tensile strength (NTS = 1.6 UTS) ofthe Type 1a specimen, which is equal to or greater than 1.2UTS.8.2 To obtain the equivalent acceptance criterion for thecoatedASTM A490 bolt, the net tensile stress at the root of thethread should also be equal to or greater than 1.2
44、 UTS. Sinced/D for fasteners is always greater than 0.8, that is greater than0.7 used with Test Method F519 notched tensile specimen, thefastener must be tested in bending to attain the same stresslevel.8.3 The acceptance criterion for EHE shall be a thresholdload in bending, b, to produce the same
45、stress or greater thanthe load in tension that produces a stress of 1.2 UTS or b 1.2UTS. Since the limit load of a bolt in bending equals2.3YS 2.0 UTS; the acceptance criterion for EHE is equiva-lent to 60% of the fast fracture load in bending, FFS(B)coated.8.3.1 Therefore for acceptance of a coatin
46、g system for A490bolts, the following condition must be met:Pth$0.6FFSB!coated(1)8.4 Bolt Size EquivalenceBased on the Fastener AnalysisDiagram (see Note 4), a smaller diameter bolt size can betested to satisfy the acceptance criterion for a larger bolt sizediameter if it attains a threshold load wi
47、th a higher value thanthe minimum value of 60% of the fracture load in bending.This ratio is defined as the hydrogen susceptibility ratio, Hsr, inTerminology F2078. The acceptance criteria is based on Hsrbeing 1.2 or 60% FFS(B).8.4.1 From the references in Note 4, the relationship be-tween two diame
48、ters is defined by the following equation:Hsr0*fd0 D0!=D05 Hsr1*fd1 D1!=D1(2)8.4.2 Using the dimensional parameters for d1and D1for alarger size bolt and inputting a value of Hsr1= 1.2, theequivalent Hsr0value for the smaller sized tested bolt with d0and D0can be calculated. These are the minimum va
49、lues for asmaller diameter bolt size to satisfy the acceptance criterion fora larger bolt size. The f(d/D) function is found in Tada, H.,Paris, P. and Irwin, G., Stress Analysis of Cracks Handbook,S 27.2.F2660 1348.4.3 This equivalence among the different sizes is summa-rized in Table 2.NOTE 4For more detail see reference: Raymond, L., Handbook ofBolts and Bolted Joints, pp. 745-747. Calculations are based on dimen-sions given in ASME B1.1-2003, Table 6. Basic Dimensions for CoarseThread Series (UNC/UNRC).8.4.4 For example, using a 1/2“D bolt, which needs 60
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