ASTM B697-88(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B697–88(Reapproved 1999)
Standard Guide for
Selection of Sampling Plans for Inspection of
Electrodeposited Metallic and Inorganic Coatings
This standard is issued under the fixed designation B 697; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope tion cost and increase quality protection. Information on
variables plans is given in Method B 762, MIL-STD-414,
1.1 This standard gives guidance in the selection of sam-
ANSI/ASQC Z1.9-1979, and Refs (1-2).
pling plans to be used in the inspection of electrodeposited and
related coatings on products for the purpose of deciding
2. Referenced Documents
whether submitted lots of coated products comply with the
2.1 ASTM Standards:
specificationsapplicabletothecoatings.ThissupplementsTest
B 602 Test Method of Attribute Sampling of Metallic and
Method B 602 by giving more information on sampling in-
Inorganic Coatings
spection and by providing additional sampling plans for the
B 762 Method of Variables Sampling of Metallic and Inor-
user who finds the limited choice of plans in Test Method
ganic Coatings
B 602 to be inadequate.
2.2 ANSI Standard:
1.2 When using a sampling plan, a relatively small part of
ANSI/ASQC Z1.9–1979 Sampling Procedures and Tables
thearticles in an inspectionlotisselectedandinspected.Based
for Inspection by Variables for Percent Nonconformance
on the results, a decision is made that the inspection lot either
2.3 Military Standards:
does or does not satisfactorily conform to the specification.
MIL-STD-105 Sampling Procedures and Tables for Inspec-
1.3 This standard also contains several sampling plans. The
tion by Attributes
plans are attribute plans, that is, in the application of the plans
MIL-STD-414 Sampling Procedures andTables for Inspec-
each inspected article is classified as either conforming or
tion by Variables for Percent Defective
nonconforming to each of the coating requirements. The
number of nonconforming articles is compared to a maximum
3. General
allowable number. The plans are simple and relatively few.
3.1 Procedure—The use of acceptance sampling consists of
Additional plans and more complex plans that cover more
a series of decisions and actions. These are listed in order
situations are given in the Refs (1-7) at the end of this guide
below and are discussed in this standard.
and in MIL-STD 105.
3.1.1 Select characteristics to be inspected,
1.4 Acceptance sampling plans are used:
3.1.2 Select type of sampling plan,
1.4.1 When the cost of inspection is high and the conse-
3.1.3 Select quality level,
quences of accepting a nonconforming article are not serious.
3.1.4 Define inspection lot,
1.4.2 When 100 % inspection is fatiguing and boring and,
3.1.5 Select sample,
therefore, likely to result in errors. In these cases a sampling
3.1.6 Inspect sample,
plan may provide greater protection than 100 % inspection.
3.1.7 Classify inspection lot, and
1.4.3 When inspection requires a destructive test. Here,
3.1.8 Dispose of inspection lot.
sampling inspection must be used.
3.2 The need for acceptance sampling arises when a deci-
1.5 Anothergeneraltypeofacceptancesamplingplanthatis
sion must be made about what to do with a quantity of articles.
not covered in these guidelines is the variables plan in which
This quantity (called the inspection lot in this guide) may be a
measured values of characteristics are analyzed by statistical
shipment from a supplier, may be articles that are ready for a
procedures. Such plans, when applicable, can reduce inspec-
1 2
This guide is under the jurisdiction of ASTM Committee B-8 on Metallic and Annual Book of ASTM Standards, Vol 02.05.
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Available from American National Standards Institute, 11 W. 42nd St., 13th
General Test Methods. Floor, New York, NY 10036.
Current edition approved Feb. 26, 1988. Published April 1988. Originally AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,700
published as B 697 – 81. Last previous edition B 697 – 81. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B697
subsequent manufacturing operation, or may be articles ready basic to the selection of a sampling plan is a decision about the
for shipment to a customer. percentage of nonconforming articles that is acceptable. If the
function of the article is so important that no nonconformers
3.3 When acceptance sampling is done, several of the
articlesintheinspectionlotareselectedatrandom(seeSection can be tolerated, acceptance sampling cannot be used. In these
cases, every article must be inspected, and, to guard against
7). These articles constitute the sample. Each article in the
sample is inspected for conformance to the requirements error, may have to be inspected twice.
3.8 The protection that an attributes sampling plan provides
placed on it. If an article meets a requirement, it is classified as
conforming. If not, it is classified as nonconforming. If the against accepting an undesirable number of nonconforming
articles is determined by the size of the sample and by the
number of nonconforming articles in the sample is no more
than a predetermined number (called the acceptance number), acceptance number. The protection provided by a plan is
usually expressed in the form of an operating characteristic
the inspection lot is accepted. If it exceeds the acceptance
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
alongthehorizontalaxisisthequalitylevelofaninspectionlot
scope of this guide because, depending on the circumstances,
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
nonconforming (Note 1).The vertical axis is the probability, as
different use, scrapped, reworked, or dealt with in some other
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, the AQL is 1.5 %. The LQL is the quality level
quality, and poorer quality mean a relatively larger percentage of
thatwillresultintherejectionofahighpercentageofincoming
nonconforming articles.
NOTE 2—In this discussion and elsewhere in this guide, it is assumed
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)ina
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.
FIG. 1 Operating Characteristic Curve for Single Sample,
3.7 Because acceptance sampling plans permit the accep-
Attributes Sampling Plan, Sample Size 555, Acceptance
tance of inspection lots that contain nonconforming articles, Number 52
B697
inspection lots; usually it is the quality level that will result in 1.5 %, theAOQ is 1.4 %.At lower incoming quality levels the
the rejection of 90 % of the incoming inspection lots. In Fig. 1 relative improvement is greater; for example, at an incoming
the LQL is 9.6 %. In this standard, AQL and LQL are defined quality level of 3 %, the AOQ is 2.3 %.
as the quality levels that will be accepted 95 and rejected 90 %
NOTE 5—The AOQs and AOQLs in this guide are calculated on the
of the time, respectively.
basis that when rejected lots are screened the nonconforming articles
3.10 Another characteristic of sampling plans that is used in
found are replaced with conforming articles. If the discarded nonconform-
this standard is the 50/50 point. This is the quality level that
ing articles are not replaced, a practice that is frequently done, the AOQs
and AOQLs will be somewhat different from those in this guide. Chapter
will result in the acceptance of half of the incoming inspection
16 of Ref (4) discusses this point.
lots. In Fig. 1 the 50/50 point is 4.8 %.
3.11 Rectifying Inspection:
3.11.3 Use of rectifying inspection will assure that with a
3.11.1 As stated in 3.4, one of the options when an inspec-
continuous series of inspection lots the average quality level of
tion lot is rejected is screening of the lot. In this procedure,
all the accepted articles, considered as a whole, will not be
called rectifying inspection, all of the articles in a rejected lot
worse than the AOQL of the sampling plan used. However,
are inspected and the nonconforming ones are removed and
rectifying inspection can significantly increase inspection costs
replacedwithconformingarticles.Thenow100 %-conforming
since every rejected inspection lot is 100 % inspected. The
inspection lot is accepted and is passed along with the
lower the quality of incoming lots, the more of them that will
inspection lots that were accepted on the basis of acceptance
berejectedandthen100 %inspected.Fig.3showshow,forthe
sampling. The addition of these 100 %-conforming inspection
sampling plan of Fig. 1 and lots of 550, the average number of
lotsimprovestheaveragequalitylevelofalltheinspectionlots
articles inspected per inspection lot increases as the quality
takentogether.Theamountthequalitylevelisimprovedcanbe
levels of incoming lots decrease. In lots containing up to about
calculated if the average quality level of incoming inspection
1.5 % nonconforming articles the increase in inspection is
lots is known. The calculations reveal that if the incoming
moderate. Beyond that point the average amount of inspection
quality level is high, few inspection lots will be rejected and
increases rapidly. At an incoming quality level of 2.1 % the
screened and so the average quality of the outgoing lots will be
amount of inspection is doubled. And with incoming quality
only slightly improved over the incoming. If the quality level
levels of 15 % virtually every inspection lot is 100 % in-
of the incoming inspection lots is low, many of the inspection
spected.
lots will be rejected and screened. The addition of this large
3.11.4 Because the cost of inspection using rectifying in-
number of 100 %-conforming lots will result in a high outgo-
spection plans is so greatly influenced by the quality level of
ing quality level. At intermediate incoming quality levels, the
incoming inspection lots, past information of that level is
outgoing quality will be poorer than these two extremes, and
necessary before choosing an AOQL. The AOQL plans in
there will be a particular incoming quality level for which the
Table1givetherangeofincomingqualitylevelforwhicheach
outgoing level will be the poorest.
plan is recommended. The cost of the inspection is also
3.11.2 When rectifying inspection is used the average qual-
determined by the size of the inspection lot and by the size of
ity level of a series of outgoing lots is called the Average
the sample. If rectifying inspection is to be used on a large
Outgoing Quality (AOQ) and the worst possible AOQ for a
scale, it is recommended that the user refer to Ref (3).It
given plan is called the Average Outgoing Quality Limit
contains plans that yield the lowest total inspection for each
(AOQL). Fig. 2 is a plot of the AOQ for the sampling plan of
combination of AOQL, incoming qualit
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