ASTM B762-90(2010)
(Test Method)Standard Test Method of Variables Sampling of Metallic and Inorganic Coatings
Standard Test Method of Variables Sampling of Metallic and Inorganic Coatings
SIGNIFICANCE AND USE
Sampling inspection permits the estimation of the overall quality of a group of product articles through the inspection of a relatively small number of product articles drawn from the group.
The specification of a sampling plan provides purchasers and sellers a means of identifying the minimum quality level that is considered to be satisfactory.
Because sampling plans yield estimates of the quality of a product, the results of the inspection are subject to error. Through the selection of a sampling plan, the potential error is known and controlled.
Sampling inspection is used when a decision must be made about what to do with a quantity of articles. This quantity may be a shipment from a supplier, articles that are ready for a subsequent manufacturing operation, or articles ready for shipment to a customer.
In sampling inspection, a relatively small number of articles (the sample) is selected randomly from a larger number of articles (the inspection lot); the sample is inspected for conformance to the requirements placed on the articles. Based on the results, a decision is made whether or not the lot conforms to the requirements.
Since only a portion of a production lot is inspected, the quality of the uninspected articles is not known. The possibility exists that some of the uninspected articles are nonconforming. Therefore, basic to any sampling inspection plan is the willingness of the buyer to accept lots that contain some nonconforming articles. The number of nonconforming articles in accepted lots is controlled by the size of the sample and the criteria of acceptance that are placed on the sample.
Acceptance sampling plans are used for the following reasons:
When the cost of inspection is high and the consequences of accepting a nonconforming article are not serious.
When 100 % inspection is fatiguing and boring and, therefore, likely to result in errors.
When inspection requires a destructive test, sampling inspection must be used.
In acc...
SCOPE
1.1 This test method provides sampling plans that are intended for use in the inspection of metallic and inorganic coatings on products for the purpose of deciding whether submitted lots of coated products comply with the specifications applicable to the coating.
1.2 The sampling plans are variables plans. In plans of this type, several articles of product are drawn from a production lot. A characteristic of the coating on the drawn articles is measured. The values obtained are used to estimate the number of articles in the lot that do not conform to a numerical limit, for example a minimum thickness. The number is compared to a maximum allowable.
1.3 Variables plans can only be used when the characteristic of interest is measurable, the test method gives a numerical measure of the characteristic, and the specification places a numerical limit on the measured value. It is also necessary that the variation of the characteristic from article to article in a production lot be normally distributed (see Appendix X2). Each article must be tested in the same way (for example, coating thickness must be measured at the same location, see X2.7) so that the values from article to article are comparable. If one or more of these conditions are not met, a variables plan cannot be used. Instead, an attributes plan must be used. These are given in Test Method B602 and Guide B697.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: B762 − 90(Reapproved 2010)
Standard Test Method of
Variables Sampling of Metallic and Inorganic Coatings
This standard is issued under the fixed designation B762; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope B602 Test Method for Attribute Sampling of Metallic and
Inorganic Coatings
1.1 This test method provides sampling plans that are
B697 Guide for Selection of Sampling Plans for Inspection
intended for use in the inspection of metallic and inorganic
of Electrodeposited Metallic and Inorganic Coatings
coatings on products for the purpose of deciding whether
2.2 ANSI Standards:
submitted lots of coated products comply with the specifica-
ANSI/ASQC Z1.9-1979 Sampling Procedures and Tables
tions applicable to the coating.
for Inspection by Variables for Percent Non-Conformance
1.2 The sampling plans are variables plans. In plans of this
ANSI/ASQC Z1.4-1981 Sampling Procedures and Tables
type, several articles of product are drawn from a production
for Inspection by Attributes
lot. A characteristic of the coating on the drawn articles is
2.3 Military Standards:
measured.Thevaluesobtainedareusedtoestimatethenumber
MIL-STD-105 Sampling Procedures and Tables for Inspec-
of articles in the lot that do not conform to a numerical limit,
tion by Attributes
for example a minimum thickness. The number is compared to
MIL-STD-414 Sampling Procedures and Tables for Inspec-
a maximum allowable.
tion by Variables for Percent Defective
1.3 Variables plans can only be used when the characteristic
3. Definitions
of interest is measurable, the test method gives a numerical
measure of the characteristic, and the specification places a
3.1 destructive test—test that destroys the tested article or
numerical limit on the measured value. It is also necessary that makes it nonconforming to a requirement.
the variation of the characteristic from article to article in a
3.2 nondestructive test—test that neither destroys the tested
production lot be normally distributed (see Appendix X2).
article nor makes it nonconforming to a requirement.
Each article must be tested in the same way (for example,
3.3 inspection lot—collection of articles of the same kind
coating thickness must be measured at the same location, see
that is submitted to inspection for acceptance or rejection as a
X2.7) so that the values from article to article are comparable.
group.
If one or more of these conditions are not met, a variables plan
cannot be used. Instead, an attributes plan must be used. These
3.4 sample—articles randomly selected from an inspection
are given in Test Method B602 and Guide B697.
lot whose quality is used to decide whether or not the
inspection lot is of acceptable quality.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3.5 standard deviation—measure of dispersion equal to the
responsibility of the user of this standard to establish appro-
square root of the mean of the squares of the deviations from
priate safety and health practices and determine the applica-
the arithmetic mean of the distribution (see 9.2.6).
bility of regulatory limitations prior to use.
4. Summary of Test Method
2. Referenced Documents
4.1 The plans in this test method provide the same protec-
2.1 ASTM Standards:
tion as the attributes plans inTables 1, 2, and 3 ofTest Method
B602 and are interchangeable with them when the conditions
necessary for variables sampling exist. This method has no
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
plan comparable to Table 4 of Test Method B602, because
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
variables plans are subject to an excessive probability of error
Test Methods.
whenthenumberofnonconformingarticlesinalotisexpected
Current edition approved April 1, 2010. Published June 2010. Originally
approved in 1986. Last previous edition approved in 2005 as B762 – 90 (2005).
DOI: 10.1520/B0762-90R10.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM 4th Floor, New York, NY 10036, http://www.ansi.org.
Standards volume information, refer to the standard’s Document Summary page on Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
the ASTM website. Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.
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B762 − 90 (2010)
TABLE 2 Level II—Sampling Plans for Nondestructive Tests,
to be approximately 1 % or less as it is for the Table 4 plan.
A
Standard Deviation Unknown
Also for this reason, comparable variables plans are not given
Inspection 50/50
for the smallest lot sizes of Tables 1 and 2 of Test Method
nk AQL LQL AOQL
Lot Size Point
B602.The plans ofTable 4, andTables 1 and 2 inTest Method
91 through 16 1.663 1.0 12 4.8 2.4
B602 are described as Level I, Level II, and Level III
281 through 29 1.649 1.7 10 5.0 2.6
respectively. For consistency, Table 1 and Table 2 of this
method are described as Level II since they are comparable to
501 through 40 1.713 1.7 8.2 4.3 2.2
Table 1 of Test Method B602, and Table 3 and Table 4 are
1 200
1 201 through 61 1.704 2.1 7.4 4.4 2.5
described as Level III.
3 200
4.2 The main advantage of a variables sampling plan over 3 201 through 92 1.778 2.0 5.9 3.8 2.2
10 000
an attributes plan is that fewer articles need to be inspected to
10 001 through 137 1.825 2.0 4.9 3.4 2.0
obtain the same protection. For example, a sample of 12 using
35 000
variables can give the same protection as a sample of 50 using Over 35 000 223 1.893 1.9 4.0 3.0 1.9
A
attributes.Ontheotherhand,moreexpensivetestmethodsmay
The AQL, LQL, 50/50 Point, and AOQL are in percent.
be required to yield the measurements required by variables
sampling.
TABLE 3 Level III—Sampling Plans for Nondestructive Tests,
4.3 Generally, thickness is the only characteristic of a
A
Standard Deviation Known
coating that meets the conditions of a variables plan given in
Inspection 50/50
nk AQL LQL AOQL
1.3.Forthatreason,theplansinthismethodaredesignedtobe
Lot Size Point
used when the specification for the characteristic in question is
51 through 6 1.432 1.8 18 7.6 3.8
aminimumvalue,whichistheusualcaseforcoatingthickness.
151 through 10 1.411 2.7 16 7.9 4.1
Variables plans can be used when the limit is a maximum and
when there are both a minimum and a maximum. Plans for
281 through 14 1.470 2.8 13 7.1 3.5
these cases are given in the references.
501 through 23 1.492 3.3 11 6.8 3.8
1 200
4.4 The sampling plans in Tables 1 and 2 of this test method
1 201 through 30 1.551 3.2 9.4 6.0 3.5
are considered to be standard for nondestructive testing and
3 200
will be used unless the buyer specifies otherwise. Tables 5 and
3 201 through 44 1.618 3.1 7.7 5.3 3.2
16 000
6 will be used for destructive testing; these plans use smaller
16 001 through 66 1.680 3.0 6.4 4.6 3.0
samples to reduce the cost of inspection with a resultant
35 000
reduction of the ability to distinguish between conforming and
Over 35 000 103 1.719 3.0 5.6 4.4 2.9
nonconforming lots. A
The AQL, LQL, 50/50 Point, and AOQL are in percent.
4.5 Additional variables plans are given in Appendix X3.
Alsofoundthereareinstructionsforthecalculationofplansfor
TABLE 4 Level III—Sampling Plans for Nondestructive Tests,
needs that are not covered.
A
Standard Deviation Unknown
Inspection 50/50
5. Significance and Use nk AQL LQL AOQL
Lot Size Point
5.1 Sampling inspection permits the estimation of the over- 51 through 12 1.433 1.7 19 7.6 3.8
all quality of a group of product articles through the inspection
151 through 19 1.410 2.6 16 7.9 3.7
of a relatively small number of product articles drawn from the
group. 281 through 29 1.470 2.8 13 7.1 3.8
501 through 48 1.494 3.3 11 6.7 3.8
1 200
TABLE 1 Level II—Sampling Plans for Nondestructive Tests, 1 201 through 66 1.551 3.2 9.4 6.0 3.5
A
Standard Deviation Known 3 200
3 201 through 102 1.618 3.1 7.7 5.3 3.2
Inspection 50/50
nk AQL LQL AOQL
16 000
Lot Size Point
16 001 through 159 1.680 3.0 6.4 4.6 3.0
91 through 7 1.664 1.1 12 4.8 2.4
35 000
Over 35 000 248 1.717 3.0 5.6 4.3 2.9
281 through 12 1.649 1.7 10 5.0 2.6
A
The AQL, LQL, 50/50 Point, and AOQL are in percent.
501 through 16 1.712 1.7 8.2 4.4 2.3
1 200
1 201 through 25 1.704 2.1 7.4 4.4 2.5
3 200
3 201 through 36 1.778 2.0 5.9 3.8 2.2
5.2 The specification of a sampling plan provides purchas-
10 000
10 001 through 52 1.829 2.0 4.9 3.4 2.1 ers and sellers a means of identifying the minimum quality
35 000
level that is considered to be satisfactory.
Over 35 000 82 1.893 1.9 4.0 2.9 1.9
A 5.3 Because sampling plans yield estimates of the quality of
The AQL, LQL, 50/50 Point, and AOQL are in percent.
a product, the results of the inspection are subject to error.
B762 − 90 (2010)
TABLE 5 Sampling Plans for Destructive Tests, Standard
5.9 Theuseofasamplingplaninvolvesthebalancingofthe
A
Deviation Known
costs of inspection against the consequences of accepting an
50/50
undesirablenumberofnonconformingarticles.Thereisalways
Inspection Lot Size nk AQL LQL
Point
a risk that a random sample will not describe correctly the
26 through 1 200 5 1.262 2.3 25 10
characteristics of the lot from which it is drawn, and that an
1 201 through 35 000 10 1.411 2.7 16 7.9
Over 35 000 14 1.519 2.5 12 6.5
unacceptable lot will be accepted or an acceptable lot will be
A
rejected. The larger the sample, the smaller this risk but the
The AQL, LQL, and 50/50 Point are in percent.
larger the cost of inspection.
5.10 To understand the risks, consider that if every article in
TABLE 6 Sampling Plans for Destructive Tests, Standard
A an inspection lot conforms to its requirements, every article in
Deviation Unknown
the sample will conform also. Such lots will be accepted (Note
50/50
Inspection Lot Size nk AQL LQL
Point 1). If only a few articles in an inspection lot are
26 through 1 200 9 1.181 2.8 27 12
nonconforming,thesampleprobablywillindicatethatthelotis
1 201 through 35 000 19 1.412 2.5 16 7.9
acceptable; but there is a small probability that the sample will
Over 35 000 34 1.497 2.8 12 6.7
indicate that the lot is unacceptable. The larger the proportion
A
The AQL, LQL, and 50/50 Point are in percent.
of nonconforming articles in an inspection lot, the more likely
it will be that the sample will indicate that the lot is unaccept-
able. If every article in an inspection lot is nonconforming, a
sample will always indicate that the lot is unacceptable.
Through the selection of a sampling plan, the potential error is
NOTE 1—Throughout this method, it is assumed that no mistakes are
known and controlled.
made in sampling, measurement, and calculation.
5.4 Sampling inspection is used when a decision must be
5.11 The probability of accepting an inspection lot that
madeaboutwhattodowithaquantityofarticles.Thisquantity
contains nonconforming items is often described in terms of
may be a shipment from a supplier, articles that are ready for
theAcceptable Quality Level (AQL) and the Limiting Quality
a subsequent manufacturing operation, or articles ready for
Level (LQL).TheAQLis the quality level that is considered to
shipment to a customer.
be acceptable. The LQL is a quality level that is considered to
5.5 In sampling inspection, a relatively small number of
be barely tolerable.Asampling plan is selected that has a high
articles(thesample)isselectedrandomlyfromalargernumber
probability of accepting lots of AQL quality and of rejecting
of articles (the inspection lot); the sample is inspected for
lots of LQL quality. In this method, the AQL given for a
conformance to the requirements placed on the articles. Based
sampling plan is the quality level of lots (expressed as the
on the results, a decision is made whether or not the lot
percentage of nonconforming articles) that have a 95 % prob-
conforms to the requirements.
ability of being accepted. The LQL is the quality level of lots
that have a 10 % probability of being accepted or, in other
5.6 Since only a portion of a production lot is inspected, the
words, a 90 % probability of being rejected. The tables in this
qualityoftheuninspectedarticlesisnotknown.Thepossibility
methodgivetheAQLandLQLofeachplan.Theyalsogivethe
exists that some of the uninspected articles are nonconforming.
50/50 point, the quality level of a lot that is just as likely to be
Therefore, basic to any sampling inspection plan is the will-
accepted as rejected.
ingness of the buyer to accept lots that contain some noncon-
forming articles. The number of nonconforming articles in
5.12 The disposition of nonconforming inspection lots is
accepted lots is controlled by the size of the sample and the
beyond the scope of this method because, depending on the
criteria of acceptance that are placed on the sample.
circumstances, lots may be returned to the supplier, kept and
5.7 Acceptance sampling plans are used for the following used, put to a different use, scrapped, reworked, or dealt with
in some other way. An alternative is rectifying inspection in
reasons:
5.7.1 When the cost of inspection is high and the conse- which rejected lots are screened and used.
quences of accepting a nonconforming article are not serious.
5.13 In rectifying inspection, when an inspection lot is
5.7.2 When 100 % inspection is fatiguing and boring and,
rejected, all of the articles in the lot are inspected and
therefore, likely to result in errors.
nonconforming ones are removed. They may be replaced with
5.7.3 When inspection requires a destructive test, sampling
conforming articles. The now 100 % conforming lot is ac-
inspection must be used.
cepted.With this practice, the average quality level for a series
5.8 In acceptance sampling by variables, the coating char- of lots taken as a whole will be better because of the addition
acteristic of each article in the sample is measured. Using the of the 100 % conforming lots. When the incoming lots are of a
arithmetic mean of these values, the standard deviation of the good quality level, the average quality level of a series of lots
process, and the factor k that is found in the Tables, a number will be even better when the rejected lots are screened and
is calculated (see 9.3). If thi
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