ASTM B697-88(2005)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B697–88(Reapproved 2005)
Standard Guide for
Selection of Sampling Plans for Inspection of
Electrodeposited Metallic and Inorganic Coatings
This standard is issued under the fixed designation B697; 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 variables plans is given in Test Method B762, MIL-STD-414,
ANSI/ASQC Z1.9-1979, and Refs (1-2).
1.1 This guide gives guidance in the selection of sampling
plans to be used in the inspection of electrodeposited and
2. Referenced Documents
related coatings on products for the purpose of deciding
2.1 ASTM Standards:
whether submitted lots of coated products comply with the
B602 Test Method for Attribute Sampling of Metallic and
specificationsapplicabletothecoatings.ThissupplementsTest
Inorganic Coatings
Method B602 by giving more information on sampling inspec-
B762 Test Method of Variables Sampling of Metallic and
tion and by providing additional sampling plans for the user
Inorganic Coatings
who finds the limited choice of plans in Test Method B602 to
2.2 ANSI Standard:
be inadequate.
ANSI/ASQC Z1.9–1979 Sampling Procedures and Tables
1.2 When using a sampling plan, a relatively small part of
for Inspection by Variables for Percent Nonconformance
thearticlesinaninspectionlotisselectedandinspected.Based
2.3 Military Standards:
on the results, a decision is made that the inspection lot either
MIL-STD-105 Sampling Procedures and Tables for Inspec-
does or does not satisfactorily conform to the specification.
tion by Attributes
1.3 This guide also contains several sampling plans. The
MIL-STD-414 Sampling Procedures andTables for Inspec-
plans are attribute plans, that is, in the application of the plans
tion by Variables for Percent Defective
each inspected article is classified as either conforming or
nonconforming to each of the coating requirements. The
3. General
number of nonconforming articles is compared to a maximum
3.1 Procedure—The use of acceptance sampling consists of
allowable number. The plans are simple and relatively few.
a series of decisions and actions. These are listed in order
Additional plans and more complex plans that cover more
below and are discussed in this standard.
situations are given in the Refs (1-7) at the end of this guide
3.1.1 Select characteristics to be inspected,
and in MIL-STD 105.
3.1.2 Select type of sampling plan,
1.4 Acceptance sampling plans are used:
3.1.3 Select quality level,
1.4.1 When the cost of inspection is high and the conse-
3.1.4 Define inspection lot,
quences of accepting a nonconforming article are not serious.
3.1.5 Select sample,
1.4.2 When 100 % inspection is fatiguing and boring and,
3.1.6 Inspect sample,
therefore, likely to result in errors. In these cases a sampling
3.1.7 Classify inspection lot, and
plan may provide greater protection than 100 % inspection.
3.1.8 Dispose of inspection lot.
1.4.3 When inspection requires a destructive test. Here,
3.2 The need for acceptance sampling arises when a deci-
sampling inspection must be used.
sion must be made about what to do with a quantity of articles.
1.5 Anothergeneraltypeofacceptancesamplingplanthatis
This quantity (called the inspection lot in this guide) may be a
not covered in these guidelines is the variables plan in which
shipment from a supplier, may be articles that are ready for a
measured values of characteristics are analyzed by statistical
subsequent manufacturing operation, or may be articles ready
procedures. Such plans, when applicable, can reduce inspec-
for shipment to a customer.
tion cost and increase quality protection. Information on
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
This guide is under the jurisdiction ofASTM Committee B08 on Metallic and Standards volume information, refer to the standard’s Document Summary page on
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test the ASTM website.
Methods. Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Current edition approved May 15, 2005. Published June 2005. Originally 4th Floor, New York, NY 10036.
approved in 1981. Last previous edition approved in 1999 as B697 – 88 (1999). Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
DOI: 10.1520/B0697-88R05. Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B697–88 (2005)
3.3 When acceptance sampling is done, several of the function of the article is so important that no nonconformers
articlesintheinspectionlotareselectedatrandom(seeSection can be tolerated, acceptance sampling cannot be used. In these
7). These articles constitute the sample. Each article in the cases, every article must be inspected, and, to guard against
sample is inspected for conformance to the requirements error, may have to be inspected twice.
placed on it. If an article meets a requirement, it is classified as 3.8 The protection that an attributes sampling plan provides
conforming. If not, it is classified as nonconforming. If the against accepting an undesirable number of nonconforming
number of nonconforming articles in the sample is no more articles is determined by the size of the sample and by the
than a predetermined number (called the acceptance number), acceptance number. The protection provided by a plan is
the inspection lot is accepted. If it exceeds the acceptance usually expressed in the form of an operating characteristic
number, the inspection lot is rejected. (OC) curve. Fig. 1 is the OC curve for the plan that calls for a
sampleof55articlesandanacceptancenumberoftwo.Plotted
3.4 The disposition of rejected inspection lots is beyond the
scope of this guide because, depending on the circumstances, alongthehorizontalaxisisthequalitylevelofaninspectionlot
expressed as the percentage of the articles in the lot that are
lots may be returned to the supplier, kept and used, put to a
different use, scrapped, reworked, or dealt with in some other nonconforming (Note 1).The vertical axis is the probability, as
apercentage,thataninspectionlotwillbeacceptedbytheplan
way. An exception is rectifying inspection (3.11) in which
(Note 4). Inspection lots with zero percent nonconforming
rejected lots are screened and used.
articles will be accepted 100 % of the time (Note 2). As the
3.5 Because the decision about the disposition of an inspec-
percentage of nonconforming articles in the inspection lot
tion lot is based on the inspection of a sample, and because
increases, the probability of acceptance decreases. For ex-
there is a chance that a sample will not be representative of an
ample, as shown in Fig. 1, an inspection lot containing 1.5 %
inspection lot, some inspection lots that have the desired
nonconforming articles has a 95 % chance of being accepted,
quality level (Note 1) will be rejected and some inspection lots
while one containing 9.6 % nonconforming articles has only a
that do not have the desired quality level will be accepted.
10 % chance of being accepted.
Thereareonlytwosituationsinwhichtheresultsofacceptance
samplingaretotallypredictable(Note2).Oneiswhenthereare
NOTE 4—The vertical axis of the OC curve can have two meanings.
no nonconforming articles in the inspection lot. There, of
One is the probability that a particular inspection lot will be accepted.The
course,willbenononconformingarticlesinthesampleandthe other meaning is the percentage of a series of lots of a given quality level
that will be accepted. The latter meaning is the one that is strictly correct
decision to accept the lot will always be made. The other
mathematically. The former meaning is also correct, as long as the
situation is when no article in the inspection lot conforms. All
inspection lot is at least ten times bigger than the sample.
of the articles in the sample will be nonconforming and the
3.9 The characteristics of a sampling plan are often ex-
decision to reject the lot will always be made (Note 3).
pressed in terms of the Acceptable Quality Level (AQL) and
NOTE 1—In this guide the term “quality level” means the percentage of
theLimitingQualityLevel(LQL).TheAQListhequalitylevel
nonconforming articles in an inspection lot or it means the average
that will result in the acceptance of a high percentage of
percentage of nonconforming articles in a series of inspection lots
incoming inspection lots; usually it is the quality level that will
received from a single source. Terms such as high quality, increased
result in the acceptance of 95 % of the incoming inspection
quality, and better quality mean a relatively smaller percentage of
nonconforming articles, while terms such as low quality, decreased
lots. In Fig. 1, theAQL is 1.5 %. The LQL is the quality level
quality, and poorer quality mean a relatively larger percentage of
thatwillresultintherejectionofahighpercentageofincoming
nonconforming articles.
inspection lots; usually it is the quality level that will result in
NOTE 2—In this discussion and elsewhere in this guide, it is assumed
the rejection of 90 % of the incoming inspection lots. In Fig. 1
that no errors are made.
NOTE 3—To be strictly correct, lots that contain no more nonconform-
ing articles than the acceptance number will always be accepted, and lots
that contain fewer conforming articles than the sample size minus the
acceptance number will always be rejected.
3.6 The discussion in 3.5 leads to two important points: (1)
acceptance sampling plans will permit the acceptance of
inspection lots that contain nonconforming articles, and (2)in
a series of inspection lots, each containing the same percentage
of nonconforming articles, some will be accepted and some
will be rejected, and the percentage of nonconforming articles
in the accepted inspection lots will be the same as in the
rejected lots. In other words, acceptance sampling does not, by
itself, result in higher quality. Rectifying inspection (3.11) will
result in higher average quality in the product leaving inspec-
tion.
3.7 Because acceptance sampling plans permit the accep-
tance of inspection lots that contain nonconforming articles,
FIG. 1 Operating Characteristic Curve for Single Sample,
basic to the selection of a sampling plan is a decision about the
Attributes Sampling Plan, Sample Size=55, Acceptance
percentage of nonconforming articles that is acceptable. If the Number=2
B697–88 (2005)
NOTE 5—The AOQs and AOQLs in this guide are calculated on the
the LQL is 9.6 %. In this standard, AQL and LQL are defined
basis that when rejected lots are screened the nonconforming articles
as the quality levels that will be accepted 95 and rejected 90 %
found are replaced with conforming articles. If the discarded nonconform-
of the time, respectively.
ing articles are not replaced, a practice that is frequently done, theAOQs
3.10 Another characteristic of sampling plans that is used in
andAOQLs will be somewhat different from those in this guide. Chapter
this standard is the 50/50 point. This is the quality level that
16 of Ref (4) discusses this point.
will result in the acceptance of half of the incoming inspection
3.11.3 Use of rectifying inspection will assure that with a
lots. In Fig. 1 the 50/50 point is 4.8 %.
continuous series of inspection lots the average quality level of
3.11 Rectifying Inspection:
all the accepted articles, considered as a whole, will not be
3.11.1 As stated in 3.4, one of the options when an inspec-
worse than the AOQL of the sampling plan used. However,
tion lot is rejected is screening of the lot. In this procedure,
rectifying inspection can significantly increase inspection costs
called rectifying inspection, all of the articles in a rejected lot
since every rejected inspection lot is 100 % inspected. The
are inspected and the nonconforming ones are removed and
lower the quality of incoming lots, the more of them that will
replacedwithconformingarticles.Thenow100 %-conforming
berejectedandthen100 %inspected.Fig.3showshow,forthe
inspection lot is accepted and is passed along with the
sampling plan of Fig. 1 and lots of 550, the average number of
inspection lots that were accepted on the basis of acceptance
articles inspected per inspection lot increases as the quality
sampling. The addition of these 100 %-conforming inspection
levels of incoming lots decrease. In lots containing up to about
lotsimprovestheaveragequalitylevelofalltheinspectionlots
1.5 % nonconforming articles the increase in inspection is
takentogether.Theamountthequalitylevelisimprovedcanbe
moderate. Beyond that point the average amount of inspection
calculated if the average quality level of incoming inspection
increases rapidly. At an incoming quality level of 2.1 % the
lots is known. The calculations reveal that if the incoming
amount of inspection is doubled. And with incoming quality
quality level is high, few inspection lots will be rejected and
levels of 15 % virtually every inspection lot is 100 % in-
screened and so the average quality of the outgoing lots will be
spected.
only slightly improved over the incoming. If the quality level
3.11.4 Because the cost of inspection using rectifying in-
of the incoming inspection lots is low, many of the inspection
spection plans is so greatly influenced by the quality level of
lots will be rejected and screened. The addition of this large
incoming inspection lots, past information of that level is
number of 100 %-conforming lots will result in a high outgo-
necessary before choosing an AOQL. The AOQL plans in
ing quality level. At intermediate incoming quality levels, the
Table1givetherangeofincomingqualitylevelforwhicheach
outgoing quality will be poorer than these two extremes, and
plan is recommended. The cost of the inspection is also
there will be a particular incoming quality level for which the
determined by the size of the inspection lot and by the size of
outgoing level will be the poorest.
the sample. If rectifying inspection is to be used on a large
3.11.2 When rectifying inspection is used the average qual-
scale, it is recommended that the user refer to Ref (3).It
ity level of a series of outgoing lots is called the Average
contains plans that yield the lowest total inspection for each
Outgoing Quality (AOQ) and the worst possible AOQ for a
combination of AOQL, incoming quality level, and inspection
...