ASTM B762-90(2005)
(Test Method)Standard Test Method of Variables Sampling of Metallic and Inorganic Coatings
Standard Test Method of Variables Sampling of Metallic and Inorganic Coatings
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 B 602 and Guide B 697.
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 2005)
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 B697 Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
1.1 This test method provides sampling plans that are
2.2 ANSI Standards:
intended for use in the inspection of metallic and inorganic
ANSI/ASQC Z1.9-1979 Sampling Procedures and Tables
coatings on products for the purpose of deciding whether
for Inspection by Variables for Percent Non-Conformance
submitted lots of coated products comply with the specifica-
ANSI/ASQC Z1.4-1981 Sampling Procedures and Tables
tions applicable to the coating.
for Inspection by Attributes
1.2 The sampling plans are variables plans. In plans of this
2.3 Military Standards:
type, several articles of product are drawn from a production
MIL-STD-105 Sampling Procedures and Tables for Inspec-
lot. A characteristic of the coating on the drawn articles is
tion by Attributes
measured.Thevaluesobtainedareusedtoestimatethenumber
MIL-STD-414 Sampling Procedures and Tables for Inspec-
of articles in the lot that do not conform to a numerical limit,
tion by Variables for Percent Defective
for example a minimum thickness. The number is compared to
a maximum allowable.
3. Terminology Definitions
1.3 Variables plans can only be used when the characteristic
3.1 destructive test—test that destroys the tested article or
of interest is measurable, the test method gives a numerical
makes it nonconforming to a requirement.
measure of the characteristic, and the specification places a
3.2 nondestructive test—test that neither destroys the tested
numerical limit on the measured value. It is also necessary that
article nor makes it nonconforming to a requirement.
the variation of the characteristic from article to article in a
3.3 inspection lot—collection of articles of the same kind
production lot be normally distributed (see Appendix X2).
that is submitted to inspection for acceptance or rejection as a
Each article must be tested in the same way (for example,
group.
coating thickness must be measured at the same location, see
3.4 sample—articles randomly selected from an inspection
X2.7) so that the values from article to article are comparable.
lot whose quality is used to decide whether or not the
If one or more of these conditions are not met, a variables plan
inspection lot is of acceptable quality.
cannot be used. Instead, an attributes plan must be used. These
3.5 standard deviation—measure of dispersion equal to the
are given in Test Method B602 and Guide B697.
square root of the mean of the squares of the deviations from
1.4 This standard does not purport to address all of the
the arithmetic mean of the distribution (see 9.2.6).
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Method
priate safety and health practices and determine the applica-
4.1 The plans in this test method provide the same protec-
bility of regulatory limitations prior to use.
tion as the attributes plans inTables 1, 2, and 3 ofTest Method
2. Referenced Documents B602 and are interchangeable with them when the conditions
2 necessary for variables sampling exist. This method has no
2.1 ASTM Standards:
plan comparable to Table 4 of Test Method B602, because
B602 Test Method for Attribute Sampling of Metallic and
variables plans are subject to an excessive probability of error
Inorganic Coatings
whenthenumberofnonconformingarticlesinalotisexpected
to be approximately 1 % or less as it is for the Table 4 plan.
ThistestmethodisunderthejurisdictionofASTMCommitteeB08onMetallic
Also for this reason, comparable variables plans are not given
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
for the smallest lot sizes of Tables 1 and 2 of Test Method
Test Methods.
B602.The plans ofTable 4, andTables 1 and 2 inTest Method
Current edition approved May 15, 2005. Published June 2005. Originally
approved in 1986. Last previous edition approved in 1999 as B762 – 90 (1999).
DOI: 10.1520/B0762-90R05.
2 3
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B762–90 (2005)
TABLE 2 Level II—Sampling Plans for Nondestructive Tests,
B602 are described as Level I, Level II, and Level III
A
Standard Deviation Unknown
respectively. For consistency, Table 1 and Table 2 of this
Inspection 50/50
method are described as Level II since they are comparable to
nk AQL LQL AOQL
Lot Size Point
Table 1 of Test Method B602, and Table 3 and Table 4 are
91 through 16 1.663 1.0 12 4.8 2.4
described as Level III.
4.2 The main advantage of a variables sampling plan over
281 through 29 1.649 1.7 10 5.0 2.6
an attributes plan is that fewer articles need to be inspected to
501 through 40 1.713 1.7 8.2 4.3 2.2
obtain the same protection. For example, a sample of 12 using
1 200
variables can give the same protection as a sample of 50 using
1 201 through 61 1.704 2.1 7.4 4.4 2.5
3 200
attributes.Ontheotherhand,moreexpensivetestmethodsmay
3 201 through 92 1.778 2.0 5.9 3.8 2.2
be required to yield the measurements required by variables
10 000
sampling.
10 001 through 137 1.825 2.0 4.9 3.4 2.0
35 000
4.3 Generally, thickness is the only characteristic of a
Over 35 000 223 1.893 1.9 4.0 3.0 1.9
coating that meets the conditions of a variables plan given in
A
The AQL, LQL, 50/50 Point, and AOQL are in percent.
1.3.Forthatreason,theplansinthismethodaredesignedtobe
used when the specification for the characteristic in question is
TABLE 3 Level III—Sampling Plans for Nondestructive Tests,
aminimumvalue,whichistheusualcaseforcoatingthickness.
A
Standard Deviation Known
Variables plans can be used when the limit is a maximum and
Inspection 50/50
when there are both a minimum and a maximum. Plans for
nk AQL LQL AOQL
Lot Size Point
these cases are given in the references.
51 through 6 1.432 1.8 18 7.6 3.8
4.4 The sampling plans inTables 1 and 2 of this test method
are considered to be standard for nondestructive testing and
151 through 10 1.411 2.7 16 7.9 4.1
will be used unless the buyer specifies otherwise. Tables 5 and
281 through 14 1.470 2.8 13 7.1 3.5
6 will be used for destructive testing; these plans use smaller
samples to reduce the cost of inspection with a resultant 501 through 23 1.492 3.3 11 6.8 3.8
1 200
reduction of the ability to distinguish between conforming and
1 201 through 30 1.551 3.2 9.4 6.0 3.5
nonconforming lots.
3 200
4.5 Additional variables plans are given in Appendix X3. 3 201 through 44 1.618 3.1 7.7 5.3 3.2
16 000
Alsofoundthereareinstructionsforthecalculationofplansfor
16 001 through 66 1.680 3.0 6.4 4.6 3.0
needs that are not covered.
35 000
Over 35 000 103 1.719 3.0 5.6 4.4 2.9
5. Significance and Use
A
The AQL, LQL, 50/50 Point, and AOQL are in percent.
5.1 Sampling inspection permits the estimation of the over-
all quality of a group of product articles through the inspection
TABLE 4 Level III—Sampling Plans for Nondestructive Tests,
A
of a relatively small number of product articles drawn from the Standard Deviation Unknown
group.
Inspection 50/50
nk AQL LQL AOQL
Lot Size Point
5.2 The specification of a sampling plan provides purchas-
ers and sellers a means of identifying the minimum quality 51 through 12 1.433 1.7 19 7.6 3.8
level that is considered to be satisfactory.
151 through 19 1.410 2.6 16 7.9 3.7
5.3 Because sampling plans yield estimates of the quality of
281 through 29 1.470 2.8 13 7.1 3.8
a product, the results of the inspection are subject to error.
Through the selection of a sampling plan, the potential error is
501 through 48 1.494 3.3 11 6.7 3.8
known and controlled.
1 200
1 201 through 66 1.551 3.2 9.4 6.0 3.5
3 200
TABLE 1 Level II—Sampling Plans for Nondestructive Tests,
3 201 through 102 1.618 3.1 7.7 5.3 3.2
A
Standard Deviation Known
16 000
16 001 through 159 1.680 3.0 6.4 4.6 3.0
Inspection 50/50
nk AQL LQL AOQL
35 000
Lot Size Point
Over 35 000 248 1.717 3.0 5.6 4.3 2.9
91 through 7 1.664 1.1 12 4.8 2.4
A
The AQL, LQL, 50/50 Point, and AOQL are in percent.
281 through 12 1.649 1.7 10 5.0 2.6
501 through 16 1.712 1.7 8.2 4.4 2.3
5.4 Sampling inspection is used when a decision must be
1 200
madeaboutwhattodowithaquantityofarticles.Thisquantity
1 201 through 25 1.704 2.1 7.4 4.4 2.5
may be a shipment from a supplier, articles that are ready for
3 200
3 201 through 36 1.778 2.0 5.9 3.8 2.2
a subsequent manufacturing operation, or articles ready for
10 000
shipment to a customer.
10 001 through 52 1.829 2.0 4.9 3.4 2.1
5.5 In sampling inspection, a relatively small number of
35 000
Over 35 000 82 1.893 1.9 4.0 2.9 1.9
articles(thesample)isselectedrandomlyfromalargernumber
A
The AQL, LQL, 50/50 Point, and AOQL are in percent. of articles (the inspection lot); the sample is inspected for
B762–90 (2005)
TABLE 5 Sampling Plans for Destructive Tests, Standard
butthereisasmallprobabilitythatthesamplewillindicatethat
A
Deviation Known
the lot is unacceptable. The larger the proportion of noncon-
50/50
forming articles in an inspection lot, the more likely it will be
Inspection Lot Size nk AQL LQL
Point
that the sample will indicate that the lot is unacceptable. If
26 through 1 200 5 1.262 2.3 25 10
every article in an inspection lot is nonconforming, a sample
1 201 through 35 000 10 1.411 2.7 16 7.9
will always indicate that the lot is unacceptable.
Over 35 000 14 1.519 2.5 12 6.5
A
The AQL, LQL, and 50/50 Point are in percent.
NOTE 1—Throughout this method, it is assumed that no mistakes are
made in sampling, measurement, and calculation.
TABLE 6 Sampling Plans for Destructive Tests, Standard
A
5.11 The probability of accepting an inspection lot that
Deviation Unknown
contains nonconforming items is often described in terms of
50/50
Inspection Lot Size nk AQL LQL
Point theAcceptable Quality Level (AQL) and the Limiting Quality
Level (LQL).TheAQLis the quality level that is considered to
26 through 1 200 9 1.181 2.8 27 12
1 201 through 35 000 19 1.412 2.5 16 7.9
be acceptable. The LQL is a quality level that is considered to
Over 35 000 34 1.497 2.8 12 6.7
be barely tolerable.Asampling plan is selected that has a high
A
The AQL, LQL, and 50/50 Point are in percent.
probability of accepting lots of AQL quality and of rejecting
lots of LQL quality. In this method, the AQL given for a
sampling plan is the quality level of lots (expressed as the
conformance to the requirements placed on the articles. Based
percentage of nonconforming articles) that have a 95 % prob-
on the results, a decision is made whether or not the lot
ability of being accepted. The LQL is the quality level of lots
conforms to the requirements.
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-
5.12 The disposition of nonconforming inspection lots is
forming articles. The number of nonconforming articles in
beyond the scope of this method because, depending on the
accepted lots is controlled by the size of the sample and the
circumstances, lots may be returned to the supplier, kept and
criteria of acceptance that are placed on the sample.
used, put to a different use, scrapped, reworked, or dealt with
5.7 Acceptance sampling plans are used for the following
in some other way. An alternative is rectifying inspection in
reasons:
which rejected lots are screened and used.
5.7.1 When the cost of inspection is high and the conse-
5.13 In rectifying inspection, when an inspection lot is
quences of accepting a nonconforming article are not serious.
rejected, all of the articles in the lot are inspected and
5.7.2 When 100 % inspection is fatiguing and boring and,
nonconforming ones are removed. They may be replaced with
therefore, likely to result in errors.
conforming articles. The now 100 % conforming lot is ac-
5.7.3 When inspection requires a destructive test, sampling
cepted.With this practice, the average quality level for a series
inspection must be used.
of lots taken as a whole will be better because of the addition
5.8 In acceptance sampling by variables, the coating char-
of the 100 % conforming lots. When the incoming lots are of a
acteristic of each article in the sample is measured. Using the
good quality level, the average quality level of a series of lots
arithmetic mean of these values, the standard deviation of the
will be even better when the rejected lots are screened and
process, and the factor k that is found in the Tables, a number
resubmitted. When incoming lots are of a poor quality level,
is calculated (see 9.3). If this number equals or exceeds the
the average quality of a series of accepted lots will again be
specified minimum, the inspection lot conforms to the require-
good because many of the incoming lots will be rejected and
ments. If it is less, the lot does not conform. If the standard
upgraded. At intermediate quality levels of incoming lots, the
deviationoftheprocessisnotknown,thestandarddeviationof
average quality level of a series of accepted lots will again be
the sample is calculated and used.
improved, but it will not be improved as much as in either of
5.9 Theuseofasamplingplaninvolvesthebalancingofthe
the above cases; and there will be an intermediate quality level
costs of inspection against the consequences of ac
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