1、Designation: B 762 90 (Reapproved 2005)Standard Test Method ofVariables Sampling of Metallic and Inorganic Coatings1This standard is issued under the fixed designation B 762; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method provides sampling plans that areintended for use in the inspection of metallic and inorganiccoat
3、ings on products for the purpose of deciding whethersubmitted lots of coated products comply with the specifica-tions applicable to the coating.1.2 The sampling plans are variables plans. In plans of thistype, several articles of product are drawn from a productionlot. A characteristic of the coatin
4、g on the drawn articles ismeasured. The values obtained are used to estimate the numberof articles in the lot that do not conform to a numerical limit,for example a minimum thickness. The number is compared toa maximum allowable.1.3 Variables plans can only be used when the characteristicof interest
5、 is measurable, the test method gives a numericalmeasure of the characteristic, and the specification places anumerical limit on the measured value. It is also necessary thatthe variation of the characteristic from article to article in aproduction lot be normally distributed (see Appendix X2).Each
6、article must be tested in the same way (for example,coating thickness must be measured at the same location, seeX2.7) so that the values from article to article are comparable.If one or more of these conditions are not met, a variables plancannot be used. Instead, an attributes plan must be used. Th
7、eseare given in Test Method B 602 and Guide B 697.1.4 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 r
8、egulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsB 697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic Coatings2.2 ANSI Standards:3ANSI/ASQC Z1.9-1979
9、 Sampling Procedures and Tablesfor Inspection by Variables for Percent Non-ConformanceANSI/ASQC Z1.4-1981 Sampling Procedures and Tablesfor Inspection by Attributes2.3 Military Standards:4MIL-STD-105 Sampling Procedures and Tables for Inspec-tion by AttributesMIL-STD-414 Sampling Procedures and Tabl
10、es for Inspec-tion by Variables for Percent Defective3. Terminology Definitions3.1 destructive testtest that destroys the tested article ormakes it nonconforming to a requirement.3.2 nondestructive testtest that neither destroys the testedarticle nor makes it nonconforming to a requirement.3.3 inspe
11、ction lotcollection of articles of the same kindthat is submitted to inspection for acceptance or rejection as agroup.3.4 samplearticles randomly selected from an inspectionlot whose quality is used to decide whether or not theinspection lot is of acceptable quality.3.5 standard deviationmeasure of
12、dispersion equal to thesquare root of the mean of the squares of the deviations fromthe arithmetic mean of the distribution (see 9.2.6).4. Summary of Test Method4.1 The plans in this test method provide the same protec-tion as the attributes plans in Tables 1, 2, and 3 of Test MethodB 602 and are in
13、terchangeable with them when the conditionsnecessary for variables sampling exist. This method has noplan comparable to Table 4 of Test Method B 602, becausevariables plans are subject to an excessive probability of errorwhen the number of nonconforming articles in a lot is expectedto be approximate
14、ly 1 % or less as it is for the Table 4 plan.Also for this reason, comparable variables plans are not givenfor the smallest lot sizes of Tables 1 and 2 of Test Method1This test method is under the jurisdiction ofASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of
15、 Subcommittee B08.10 onTest Methods.Current edition approved May 15, 2005. Published June 2005. Originallyapproved in 1986. Last previous edition approved in 1999 as B 762 90 (1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.o
16、rg. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Se
17、ction D, 700 Robbins Ave., Philadelphia, PA 19111-50981Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.B 602. The plans of Table 4, and Tables 1 and 2 in Test MethodB 602 are described as Level I, Level II, and Level IIIrespectively.
18、For consistency, Table 1 and Table 2 of thismethod are described as Level II since they are comparable toTable 1 of Test Method B 602, and Table 3 and Table 4 aredescribed as Level III.4.2 The main advantage of a variables sampling plan overan attributes plan is that fewer articles need to be inspec
19、ted toobtain the same protection. For example, a sample of 12 usingvariables can give the same protection as a sample of 50 usingattributes. On the other hand, more expensive test methods maybe required to yield the measurements required by variablessampling.4.3 Generally, thickness is the only char
20、acteristic of acoating that meets the conditions of a variables plan given in1.3. For that reason, the plans in this method are designed to beused when the specification for the characteristic in question isa minimum value, which is the usual case for coating thickness.Variables plans can be used wh
21、en the limit is a maximum andwhen there are both a minimum and a maximum. Plans forthese cases are given in the references.4.4 The sampling plans in Tables 1 and 2 of this test methodare considered to be standard for nondestructive testing andwill be used unless the buyer specifies otherwise. Tables
22、 5 and6 will be used for destructive testing; these plans use smallersamples to reduce the cost of inspection with a resultantreduction of the ability to distinguish between conforming andnonconforming lots.4.5 Additional variables plans are given in Appendix X3.Also found there are instructions for
23、 the calculation of plans forneeds that are not covered.5. Significance and Use5.1 Sampling inspection permits the estimation of the over-all quality of a group of product articles through the inspectionof a relatively small number of product articles drawn from thegroup.5.2 The specification of a s
24、ampling plan provides purchas-ers and sellers a means of identifying the minimum qualitylevel that is considered to be satisfactory.5.3 Because sampling plans yield estimates of the quality ofa product, the results of the inspection are subject to error.Through the selection of a sampling plan, the
25、potential error isknown and controlled.5.4 Sampling inspection is used when a decision must bemade about what to do with a quantity of articles. This quantitymay be a shipment from a supplier, articles that are ready fora subsequent manufacturing operation, or articles ready forshipment to a custome
26、r.TABLE 1 Level IISampling Plans for Nondestructive Tests,Standard Deviation KnownAInspectionLot SizenkAQL LQL50/50PointAOQL91 through2807 1.664 1.1 12 4.8 2.4281 through50012 1.649 1.7 10 5.0 2.6501 through1 20016 1.712 1.7 8.2 4.4 2.31 201 through3 20025 1.704 2.1 7.4 4.4 2.53 201 through10 00036
27、1.778 2.0 5.9 3.8 2.210 001 through35 00052 1.829 2.0 4.9 3.4 2.1Over 35 000 82 1.893 1.9 4.0 2.9 1.9AThe AQL, LQL, 50/50 Point, and AOQL are in percent.TABLE 2 Level IISampling Plans for Nondestructive Tests,Standard Deviation UnknownAInspectionLot SizenkAQL LQL50/50PointAOQL91 through28016 1.663 1
28、.0 12 4.8 2.4281 through50029 1.649 1.7 10 5.0 2.6501 through1 20040 1.713 1.7 8.2 4.3 2.21 201 through3 20061 1.704 2.1 7.4 4.4 2.53 201 through10 00092 1.778 2.0 5.9 3.8 2.210 001 through35 000137 1.825 2.0 4.9 3.4 2.0Over 35 000 223 1.893 1.9 4.0 3.0 1.9AThe AQL, LQL, 50/50 Point, and AOQL are in
29、 percent.TABLE 3 Level IIISampling Plans for Nondestructive Tests,Standard Deviation KnownAInspectionLot SizenkAQL LQL50/50PointAOQL51 through1506 1.432 1.8 18 7.6 3.8151 through28010 1.411 2.7 16 7.9 4.1281 through50014 1.470 2.8 13 7.1 3.5501 through1 20023 1.492 3.3 11 6.8 3.81 201 through3 20030
30、 1.551 3.2 9.4 6.0 3.53 201 through16 00044 1.618 3.1 7.7 5.3 3.216 001 through35 00066 1.680 3.0 6.4 4.6 3.0Over 35 000 103 1.719 3.0 5.6 4.4 2.9AThe AQL, LQL, 50/50 Point, and AOQL are in percent.TABLE 4 Level IIISampling Plans for Nondestructive Tests,Standard Deviation UnknownAInspectionLot Size
31、nkAQL LQL50/50PointAOQL51 through15012 1.433 1.7 19 7.6 3.8151 through28019 1.410 2.6 16 7.9 3.7281 through50029 1.470 2.8 13 7.1 3.8501 through1 20048 1.494 3.3 11 6.7 3.81 201 through3 20066 1.551 3.2 9.4 6.0 3.53 201 through16 000102 1.618 3.1 7.7 5.3 3.216 001 through35 000159 1.680 3.0 6.4 4.6
32、3.0Over 35 000 248 1.717 3.0 5.6 4.3 2.9AThe AQL, LQL, 50/50 Point, and AOQL are in percent.B 762 90 (2005)25.5 In sampling inspection, a relatively small number ofarticles (the sample) is selected randomly from a larger numberof articles (the inspection lot); the sample is inspected forconformance
33、to the requirements placed on the articles. Basedon the results, a decision is made whether or not the lotconforms to the requirements.5.6 Since only a portion of a production lot is inspected, thequality of the uninspected articles is not known. The possibilityexists that some of the uninspected ar
34、ticles are nonconforming.Therefore, basic to any sampling inspection plan is the will-ingness of the buyer to accept lots that contain some noncon-forming articles. The number of nonconforming articles inaccepted lots is controlled by the size of the sample and thecriteria of acceptance that are pla
35、ced on the sample.5.7 Acceptance sampling plans are used for the followingreasons:5.7.1 When the cost of inspection is high and the conse-quences of accepting a nonconforming article are not serious.5.7.2 When 100 % inspection is fatiguing and boring and,therefore, likely to result in errors.5.7.3 W
36、hen inspection requires a destructive test, samplinginspection must be used.5.8 In acceptance sampling by variables, the coating char-acteristic of each article in the sample is measured. Using thearithmetic mean of these values, the standard deviation of theprocess, and the factor k that is found i
37、n the Tables, a numberis calculated (see 9.3). If this number equals or exceeds thespecified minimum, the inspection lot conforms to the require-ments. If it is less, the lot does not conform. If the standarddeviation of the process is not known, the standard deviation ofthe sample is calculated and
38、 used.5.9 The use of a sampling plan involves the balancing of thecosts of inspection against the consequences of accepting anundesirable number of nonconforming articles. There is alwaysa risk that a random sample will not describe correctly thecharacteristics of the lot from which it is drawn, and
39、 that anunacceptable lot will be accepted or an acceptable lot will berejected. The larger the sample, the smaller this risk but thelarger the cost of inspection.5.10 To understand the risks, consider that if every article inan inspection lot conforms to its requirements, every article inthe sample
40、will conform also. Such lots will be accepted (Note1). If only a few articles in an inspection lot are nonconform-ing, the sample probably will indicate that the lot is acceptable;but there is a small probability that the sample will indicate thatthe lot is unacceptable. The larger the proportion of
41、 noncon-forming articles in an inspection lot, the more likely it will bethat the sample will indicate that the lot is unacceptable. Ifevery article in an inspection lot is nonconforming, a samplewill always indicate that the lot is unacceptable.NOTE 1Throughout this method, it is assumed that no mi
42、stakes aremade in sampling, measurement, and calculation.5.11 The probability of accepting an inspection lot thatcontains nonconforming items is often described in terms ofthe Acceptable Quality Level (AQL) and the Limiting QualityLevel (LQL). TheAQL is the quality level that is considered tobe acce
43、ptable. The LQL is a quality level that is considered tobe barely tolerable. A sampling plan is selected that has a highprobability of accepting lots of AQL quality and of rejectinglots of LQL quality. In this method, the AQL given for asampling plan is the quality level of lots (expressed as theper
44、centage of nonconforming articles) that have a 95 % prob-ability of being accepted. The LQL is the quality level of lotsthat have a 10 % probability of being accepted or, in otherwords, a 90 % probability of being rejected. The tables in thismethod give theAQLand LQLof each plan. They also give the5
45、0/50 point, the quality level of a lot that is just as likely to beaccepted as rejected.5.12 The disposition of nonconforming inspection lots isbeyond the scope of this method because, depending on thecircumstances, lots may be returned to the supplier, kept andused, put to a different use, scrapped
46、, reworked, or dealt within some other way. An alternative is rectifying inspection inwhich rejected lots are screened and used.5.13 In rectifying inspection, when an inspection lot isrejected, all of the articles in the lot are inspected andnonconforming ones are removed. They may be replaced withc
47、onforming articles. The now 100 % conforming lot is ac-cepted. With this practice, the average quality level for a seriesof lots taken as a whole will be better because of the additionof the 100 % conforming lots. When the incoming lots are of agood quality level, the average quality level of a seri
48、es of lotswill be even better when the rejected lots are screened andresubmitted. When incoming lots are of a poor quality level,the average quality of a series of accepted lots will again begood because many of the incoming lots will be rejected andupgraded. At intermediate quality levels of incomi
49、ng lots, theaverage quality level of a series of accepted lots will again beimproved, but it will not be improved as much as in either ofthe above cases; and there will be an intermediate quality levelwhere the degree of improvement is the least. This improvedquality level is called the Average Outgoing Quality Limit(AOQL). It is the worst condition that can occur underrectifying inspection. The tables give the AOQL for each plan.There is no AOQL for the plans used with destructive testsbecause destructive tests cannot be used to screen rejected lots.NOTE 2The AOQLs given
