Designation: F725 − 03 (Reapproved 2013)Standard Practice forDrafting Impact Test Requirements In Thermoplastic PipeAnd Fittings Standards1This standard is issued under the fixed designation F725; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last 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 practice describes a procedure for setting up impacttest requirements on the basis of test data obtained by TestMethod D2444.1.2 This practice is applicable to thermoplastic pipe andfittings.1.3 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 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 health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2444 Test Method for Determination of the Impact Resis-tance of Thermoplastic Pipe and Fittings by Means of aTup (Falling Weight)3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 binomial probability equation—the equation that de-fines the chance for exactly r specimens to pass, when n aretested, given p, the chance that a single specimen chosen atrandom will pass. It is expressed as follows:rPn5n!r!~n 2 r! !pr~1 2 p!n2r(1)NOTE 1—The factorial of zero is one.3.1.2 binomial test—a test that has only two possible results(for example, pass or fail, heads or tails, true or false).3.1.3 mean strength—the average strength of the total popu-lation (see Note 2).3.1.4 OC curve (operating characteristic curve)— a graphthat illustrates the chance of success or failure when a givenspecification format is employed, given any quality level from0 to 1 (0 to 100 % passing in the lot from which test specimensare selected).3.1.5 probability graph paper—commercially availablegraph paper that provides straight-line plots when the distribu-tion of attributes is normal. For a discussion on the use ofproability graph paper, see Test Method D2444 Appendix X2.3.1.6 specification format—the rules set forth by the testrequirement, including the number of specimens to be testedand the minimum acceptable number of passes.3.1.7 standard deviation—a statistical term that relates tothe size of the expected variation in test results.NOTE 2—The terms “mean,” “normal distribution,” and “standarddeviation” are dealt with in elementary statistics textbooks.4. Summary of Practice4.1 Round-robin tests of representative pipe and fittingsspecimens are performed to identify the energy levels at which90 % or more of the specimens in acceptable lots will pass. Apreferred test format is listed. The B-tup and the V-blockholder, and room-temperature conditioning and tests are pre-ferred choices.5. Significance and Use5.1 This practice is used for drafting impact test specifica-tion requirements, and it presupposes no special familiaritywith statistical methods. It provides for specification valuesthat will pass acceptable lots with a high degree of certainty.The impact test requirement is intended to discriminate be-tween acceptable materials and manufacturing methods andthose which are not; it is not a simulated service test.6. Procedure6.1 Test thermoplastic pipe or fittings specimens in accor-dance with Test Method D2444, and plot the test results onprobability graph paper.1This practice is under the jurisdiction of ASTM Committee F17 on PlasticPiping Systems and is the direct responsibility of Subcommittee F17.40 on TestMethods.Current edition approved Aug. 1, 2013. Published October 2013. Originallyapproved in 1981. Last previous edition approved in 2008 as F725 – 03(2008)ε1.DOI: 10.1520/F0725-03R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.2 It will be clear, from the probability paper plot, that theenergy level where 98 % or 99 % of all specimens would passwill be low. On the one hand, when the test format requires thatfive of five, or six of six, or nine or ten of ten tested shall pass,or the lot rejected, then the specified energy levels mustcorrespond to these levels (see Fig. 1, the operating character-istic (OC) curve for the “nine or ten of ten” test format). On theother hand, five of five, six of six, and nine or ten of ten testsat low energy levels will not screen marginal or poor lotseffectively. (See Fig. 1 again).6.3 A format which will accept reliably when 90 % or moreof the specimens in acceptable lots would pass, and rejectreliably when 60 % or fewer would pass, is as follows:6.3.1 “X.X Test ten specimens. When nine or ten pass,accept the lot. When six or fewer pass, reject the lot. Whenseven or eight pass, test ten additional specimens. When 17 ormore of 20 pass, accept the lot. When 13 or fewer of 20 pass,reject the lot. When 14, 15, or 16 pass, test 20 additionalspecimens. When 32 or more of 40 pass, accept the lot. When31 or fewer pass, reject the lot.”6.3.2 The OC curve for this format is illustrated in Fig. 2.6.4 Specimen Length—The pipe specimen length should be6 in. (150 mm) 61⁄4 in. (6mm).6.5 Choice of Tup and Holder—The B tup is preferred. Itprovides a good compromise between energy concentration inthe specimen (and therefore reduced test energy levels), andresistance to damage in service. The V-block holder is pre-ferred for pipe specimens; it provides for greater energyconcentration, and for failures in a range of thin-walledspecimens which would merely flatten on the flat-plate holder.6.6 Test Conditions—Room-temperature tests are preferred.They can be performed by the manufacturer on a timely basis,so that the size of questionable or defective inventories isminimized. Binomial tests are relatively crude, unless largenumbers of specimens are subjected to test. The expense andinconvenience of low-temperature conditioning render it a poorchoice (study Fig. 1 together with a data plot performed inaccordance with Test Method D2444 to fully grasp the meritsof this statement).7. Multiple-Product Standards7.1 Many thermoplastic pipe and fittings specifications listlarge numbers of products. Test Method D2444 requires that atleast 100 test specimens shall be employed for each single testrun in order that the impact properties can be measured withuseful accuracy. The cost of round-robin tests on each size ofthe products in the standard may approach or exceed the valueof the information to be obtained.7.2 Testing costs can be significantly reduced by performingpreliminary tests on the largest sizes listed, to determinewhether or not a cut-off point exists above which all specimenswill pass at an energy level of 300 ft·lbf (407 J) (ordinarily thehighest test energy level listed in a thermoplastic pipe orfittings impact test requirement).7.2.1 Following these tests, a limited number of represen-tative sizes can be selected, and round-robin testing performed.7.2.2 The results of these tests are analyzed. List the energylevels where the failure level was 10 % for each size tested, anddivide the energy levels by the specimen volumes in cubicinches. Plot the results against the specimen outside diameters,and label the points if it is a multiple SDR specification. In aspecification which included 25 sizes of pipe, and seven SDRseries, for example, three sizes each of three different SDRseries of pipe might be tested preliminarily. The points for eachSDR series would be connected with a curve, and from theplots the appropriate trial energy levels for six untested sizesand SDR’s calculated.7.3 One hundred test specimens of each of the six untestedsizes would be prepared, and subjected to test. If 85 to 95specimens in each lot passed, the degree of correlation wouldbe good.7.4 Depending upon the degree of correlation obtained,proceed to calculate the test energy levels for each untestedFIG. 1 O.C. Curve for Nine or Ten of TenFIG. 2 O.C. Curve for Section 6.3F725 − 03 (2013)2size, factor all energy levels back by an appropriate amount anddraft the test specification proposal, or else conduct additionaltests.7.5 The tup weight and style listed in the proposal should bethe same as that used for the preliminary tests.8. Special Considerations8.1 Fittings—The flat-plate holder is employed for fittingsimpact tests. Shims may be required, depending on fittingsconfiguration. Fittings should be impacted on a horizontalsurface, as close to the center of mass as is practical.Ordinarily, the specification will require that half the fittings beimpacted on one side, and half on the other.8.2 Thin-Walled Pipe—Thin-walled pipe may undergo com-plete closure without failure (particularly if the flat-plate holderis employed). Impact testing may still serve a useful purpose,however, since the energy levels required to flatten acceptablespecimens may result in failure of improperly manufacturedspecimens.8.3 Yard-Aged Pipe—The impact test is not ordinarily speci-fied on yard-aged pipe since many thermoplastic pipe materialsare subject to reduction in impact strength as the result ofexposure to ultraviolet rays.9. Keywords9.1 drafting impact; drafting impact requirements; impact;plastic pipe; plastic tubing; thermoplastic pipe; thermoplastictubingAPPENDIXES(Nonmandatory Information)X1. THE OPERATING CHARACTERISTIC (OC) CURVEX1.1 Purpose—The OC curve gives an accurate picture ofthe impact-test relationship between a particular test sampleand the total population. Specifically, the curve provides thechance of success of a sample when given testing regimen isemployed. This relationship is ordinarily too complex to bearrived at on the basis of guesswork.X1.2 Constructing the OC Curve—Start by listing the num-ber of ways in which success can be achieved (For example, ina “7 or more out of 10” specification format, the lot is acceptedwhen 7, 8, 9, or 10 out of 10 specimens pass.) Use the binomialprobability equation to obtain an expression for the chance thateach of these events will occur. (See example.) Evaluate thechances, substituting values for p ranging from 0 to 1. Sum thechances of success, for each chosen value of p. Plot the results(chance of success, against p) to obtain the curve.Example:OC Curve for a “7 or more out of 10” specificationformat. The chance that 7 out of 10 will pass equals,10!7!~3!!p7~1 2 p!3or 120 p7~1 2 p!3(X1.1)Substitute values ranging from 0.1 to 0.9 for p, and tabulatethe results:p7P100.10.0000.20.0010.30.0090.40.0420.50.1170.60.2150.70.2670.80.2010.90.057In like manner, tabulate the chance that 8, 9, or 10 will pass.p 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9Odds of: 7 0.000 0.001 0.009 0.042 0.117 0.215 0.267 0.201 0.0578 0.000 0.000 0.001 0.011 0.044 0.121 0.233 0.302 0.1949 0.000 0.000 0.000 0.002 0.010 0.040 0.121 0.268 0.38710 0.000 0.000 0.000 0.000 0.001 0.006 0.028 0.107 0.349Totals: 0.000 0.001 0.010 0.055 0.172 0.382 0.649 0.878 0.987When the totals are plotted against p, the OC curve results.Note that calculation increments smaller than 0.1 will providemore accuracy. A spreadsheet is useful in evaluating thebinomial probability equation.F725 − 03 (2013)3X2. MEASURING CONFORMANCE TO EXISTING TEST REQUIREMENTSX2.1 A variety of impact test specification formats are incurrent use. The information provided in the OC curve for eachof them can be expressed in mathematical terms. To identifythe chance that a given manufacturing process will pass the testrequirement, select at least 100 test specimens, and subjectthem to the impact test listed. Express the decimal percentpassing as p, and substitute in the appropriate equation: For a5 out of 5 test requirement, Psuccess= p5For a 6 out of 6 test requirement, Psuccess= p6For a 10 out of 10 test requirement, Psuccess= p10For a 12 out of 12 test requirement, Psuccess= p12Fora5of5or9of10test, Psuccess= p5(1+5p4−5p5)Fora6of6or11of12test, Psuccess= p6(1+6p5−6p6)Fora9ormore out of 10 test, Psuccess= p9(10−9p)Fora7ormore out of 10 test, Psuccess= 120 p7− 315p8+ 280p9−84p10For the procedure listed in 6.3, the formula is: 3 225p36(1 −p)4+75300p35(1 − p)5+ 828 750p34(1 − p)6+ 5 728 500p33(1 − p)7+ 62 312 400p32(1 − p)8+ 570p17(1 − p )3+45p18(1 − p)2+10p9(1 − p)+p10X2.2 The results from a 100-specimen test may not corre-late accurately with the quality level in the population. Thestandard error for a 100-specimen test is approximately 0.05(68 % of the time the measured results will not be in error bymore than 0.05, and 95.5 % of the time they will not be in errorby more than 0.10). If better accuracy is required then morespecimens should be tested. The approximate equation for thestandard error is (P(1 − P)/N)1/2.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users 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 consideration at a meeting of theresponsible technical committee, which you may attend. 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