ISO/R 1260:1970
(Main)Withdrawal of ISO/R 1260-1970
Withdrawal of ISO/R 1260-1970
Annulation de l'ISO/R 1260-1970
General Information
Relations
Standards Content (Sample)
UJX 591.873.6
Ref. No. : ISO/R 1260-1970 (E)
IS0
I NTERN AT1 O N A L O R G AN IZ AT1 O N FOR S TA N DARD IZATION
IS0 RECOMMENDATION
R 1260
GUIDE TO THE USE OF IS0 RECOMMENDATION R 390,
"SAMPLING AND INSPECTION OF ASBESTOS-CEMENT PRODUCTS"
1 çt EDITION
November 1970
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
---------------------- Page: 1 ----------------------
-2-
FOREWORD
The IS0 Recommendation R 390, Sampling and inspection of asbestoscement products, was drawn up by Technical
Committee ISO/TC 77, Products in asbestos-cement, the Secretariat of which is held by the Association Suisse de
Normalisation.
The Committee has studied the American Military Standards 105 B* and 4 14 and has used many of the principles
underlying these in the drawing up of IS0 Recommendation R 390. It was felt, however, that the relationship between
manufacturer and purchaser of asbestos-cement products is very often quite different from the typical relationship in
military procurements. For this and various other reasons the Committee decided to prepare its own Recommendation
W'
concerning asbestos-cement products and an associated Guide.
With respect to the Guide it is also appropriate to refer to additional works of a more extensive character, for example :
Administration of sampling procedures for acceptance inspection, Handbook H 105, Department of Defense,
(1)
Washington D.C., 1954**.
Defence guide to sampling inspection, Ministry of Defence, London, 1962***.
(2)
Mathematical and statistical principles underlying Military Standard 414, Department of Defense,
(3)
Washington D.C., 1958.
Anybody interested in systems of sampling inspection will profit from reading these handbooks.
The present Guide, however, has the much more limited purpose of explaining the use of the very simple collection
of sampling plans in IS0 Recommendation R 390 which represents a balanced compromise between theoretical
statistical points of view and practical economical considerations. It is the hope of the Commiteee that the sampling
plans will prove applicable in practice, and they will certainly give a safer basis for the distinction between good and
inferior material than do the rules and methods hitherto used, thus providing greater protection to the user.
The sampling plans recommended have approximately the same properties as certain plans for which the acceptable v
quality level (AQL) is equal to 4 % in the Military Standards studied.
The Committee has found it useful to include in the Guide an additional section dealing with the conditions under
which a rejected lot may be resubmitted for inspection.
*
The latest edition is now (1969) No. 1 OS D.
**
The latest edition is now (1969) : H 53, Guide to sampling inspection.
***
The 1966 edition of the Defence Guide has not been taken into account by the Committee.
---------------------- Page: 2 ----------------------
-3- ISO/R 1260-1970 (
IS0 Recommendation R 1260 November 1970
GUIDE TO THE USE OF IS0 RECOMMENDATION R 390,
"SAMPLING AND INSPECTION OF ASBESTOS-CEM ENT PRODUCTS"
1. SCOPE
This IS0 Recommendation explains in more detail than in IS0 Recommendation R 390 the rules laid down for
batching, sampling and inspection, and clarifies the consequences of using the methods of sampling inspection
recommended. Also, a number of examples are given. In addition, it describes the conditions under which rejected
lots can be resubmitted for inspection.
2. UNIT OF PRODUCT
The term unit of product means the entity to be inspected in order to determine its quality characteristics. The
unit of product is specified in the relevant IS0 Recommendation.
The unit of product is used as a counting unit in determining lot size, sample size, number of conforming units,
etc.
3 . CONFORMING AND NON-CONFORMING UNITS
A conforming unit is a unit of product having quality characteristics in conformity with the specified requirements
in the relevant IS0 Recommendation.
Examples :
IS0 Recommendation R 39 1, Building and sanitary pipes in asbestos-cement, (clause 4.3.1) specifies :
The unit bursting stress R, of pipes of type A should be not less than 100 kgf/cm2 [ 10 MN/m2 1.
This means that a building and sanitary pipe of type A (i.e. one unit of product) having R, equal to or
larger than 100 kgf/cm2 (10 MN/m2) is a conforming unit, whereas a pipe having R, less than 100 kgf/cm2
(10 MN/m2) is a non-conforming unit.
IS0 Recommendation R 393, Asbestos-cement corrugated sheets for roofing and cladding, (clause 2.5.3)
specifies : During the 24 hours of the impermeability test, traces of moisture may appear on the lower
surface, but in no instance should there be any formation of drops of water.
This means that the corrugated sheet from which the test piece is cut and which shows formation of drops
of water during testing is a non-conforming unit.
---------------------- Page: 3 ----------------------
-4- ISO/R 1260-1970 (E
4. INSPECTION LOT
An inspection lot is a collection of units of product which is accepted or rejected as a whole, depending on the
quality characteristics established by inspection of the units of product drawn from the lot.
The manufacturer should arrange for the dividing of the consignment into inspection lots and provide for
identification and segregation of each lot. It is important to maintain a separate identity until a decision
regarding acceptance or rejection of the lot has been taken on the basis of the results of the sampling and testing.
The inspection lot should be presented in such a form that every unit of product is accessible as far as practically
possible.
Inspection lots should be homogeneous, i.e. consist of units of product made under essentially the same conditions.
This may be attained by forming the lots from units that are produced
- within a relatively short period;
- from similar raw materials;
- by means of similar moulds (or patterns);
- under similar conditions of manufacture, hardening and maturing, etc.
It should be emphasized that by selection of homogeneous lots, the system of sampling inspection employed
will lead to a better discrimination between lots of good quality and lots of bad quality.
The relative sample size - i.e. the sample size as a fraction of the lot size - is decreased considerably as the lot
size is increased. Therefore, taking into account the costs of sampling, inspection and testing, it will be advantageous
to use as large inspection lots as possible, subject to the limitation discussed above with respect to the homogeneity
of the inspection lot. Also the discriminating power of the sampling system will increase with increasing sample
size.
It is therefore recommended that the parties concerned should agree upon a maximum lot size as large as possible
without coming into conflict with the homogeneity requirements and other obviously practical considerations.
To avoid unreasonable inspection and testing costs for small lots, a minimum inspection lot size should also be
agreed upon. In the event of agreement not being reached, the figures for maximum and minimum inspection
lot sizes given in the relevant IS0 Recommendation should be used.
Example :
Size of Relative
Sample size
sample size
inspection lot
4 2%
200 '
0.75 %
2 O00 15
0.175 %
20 O00 35
---------------------- Page: 4 ----------------------
-5-
ISO/R 1260-1970 (E
5. DIVISION OF A CONSIGNMENT INTO INSPECTION LOTS
By a consignment is meant a delivery or the part of a delivery which comprises units of the same category.
Examples :
Sheets of same profile but of different lengths may be regarded as of the same category.
Sheets of different profiles are regarded as of different categories.
Pipes of same diameter, class, type, or series, but of different lengths, may be regarded as of the same
category.
Pipes of different diameters are regarded as of different categories.
Pipes of same diameter but of different classes or types are regarded as of different categories.
Any consignment which is known to be, or is expected to be, non-homogeneous as regards any of the properties
to be tested by sampling should be divided by the manufacturer into assumed homogeneous sub-consignments
prior to the division into inspection lots.
Any homogeneous consignment or sub-consignment should be divided by the manufacturer into inspection lots.
If larger than the minimum inspection lot size, any fraction of a consignment remaining after the highest possible
number of maximum inspection lots has been taken out forms an inspection lot. Similarly, if larger than the
minimum inspection lot size, any homogeneous consignment or sub-consignment smaller than the maximum
inspection lot size forms an inspection lot.
Consignments or fractions of consignments smaller than the minimum inspection lot size are not submitted to
sampling and testing.
However, should the testing of one or more of the inspection lots justify rejection of any of these lots the
parties may agree to disregard this provision and to submit the remaining fraction to sampling and inspection.
Example to show the importance of having the largest possible inspection lot :
Suppose that a consignment consists of 1400 building and sanitary pipes of 250 mm diameter and that
the maximum and the minimum inspection lot sizes agreed upon are 400 and 100 pipes respectively
(see IS0 Recommendation R 391, clause 4.2.2), then the consignment should be divided into 3 inspection
lots of size 400 and 1 inspection lot of size 200. According to Table 1 of IS0 Recommendation R 390,
the sample size for lots of size 400 is 5 pipes and for lots of size 200 is 4 pipes, making a total of 19 pipes.
If the consignment consists of 1250 pipes, it is divided into 3 inspection lots of 400 pipes - from each
lot 5 pipes, totalling 15, are drawn - and a remainder of 50 pipes which is not normally submitted to
sampling and testing.
If the parties had instead agreed upon a maximum inspection lot size of 1500 pipes, and the same minimum
lot size, then the sample size would in both cases have been 10 pipes, which represents a saving of 9 and
5 pipes respectively.
---------------------- Page: 5 ----------------------
-6- ISO/R 1960-1970 (E
6. SAMPLING
A sample comprises one or more units of product drawn from an inspection lot. Since the decision to accept
or reject the lot depends on the quality of the units of product in the sample, it is of the utmost importance
that the sample is representative of the lot. This can be achieved by drawing the units at random from the lot,
which means that each unit of the lot should have an equal chance of being included in the sample. Ideally,
the units of product should be numbered, and by drawing numbers at random as in a lottery the units of the
sample should be determined. Instead of actually drawing numbers at random, a table of random numbers may
be used.
In practice, truly random sampling from large lots may be difficult. It should, however, always be ensured that
sample units of product are drawn from all parts of the lot and that units are selected without regard to their
expected quality.
The drawing of samples is normally carried out by the purchaser, in the presence of a representative of the
manufacturer, who has the right to advise the purchaser as to the correct way of drawing samples, so as to
avoid common mistakes illustrated by the following examples.
Examples :
From a stack of 100 corrugated sheets from which a sample of 3 should be drawn the 3 top sheets should
not be taken. Further, the 3 bottom sheets, or the top sheet, the centre sheet, and the bottom sheet
should not be taken.
Moreover, if a sample of 3 should be taken from a pile of 100 sheets, the purchaser should not be allowed
to go through the stack as the leaves are turned in a book in order to “select” the samples. On the
contrary, he should mark on the edges the 3 sheets he desires to be tested while the pile is still intact.
When a consignment of sheets or slates is placed, for instance, on several pallets or in several piles,
the units of product of the sample should not be drawn only from the piles that are easiest of access.
If it appears, for instance, that there are different climatic conditions in the part of the stock shed where
the consignment is stored (but not so much as to make the consignment non-homogeneous), the different
climatic conditions should be represented in the sample, and the sampling should be carried out as far as
possible without regard to the “expected properties” of the units of product of the sample.
A unit of product which has been marked during the sampling may later appear to be unsuitable for
testing. It might occur, for instance, that one of the sheets which the purchaser has marked in a stack
is found to be completely broken and unsuitable as a sample. Commor? sense should then be applied and
a neighbouring sheet substituted for the failing sample, or the sample should be regarded as a non-conforming
unit of product. In the case illustrated, the purchaser and the manufacturer may alternatively agree to take
out the whole stack of the consignment and insert another.
Both parties should keep in mind the fact that random sampling is the ideal and that they should apply common
sense to get as near to the ideal as possible.
---------------------- Page: 6 ----------------------
-7-
ISO/R 1260-1970 (E
7. DEFINITIONS OF INSPECTION BY ATTRIBUTES AND INSPECTION BY VARIABLES
In inspection by attributes the unit of product is classified as conforming or non-conforming with respect to
each of the quality requirements specified in the relevant IS0 Recommendation.
In inspection by variables the quality characteristic specified in the relevant IS0 Recommendation is measured
on a numerical scale and the values found by measuring the units of product sampled are taken into account.
The results of inspection by variables may therefore always be converted to attributes. For instance, a quality
characteristic of the pipes of type A is the unit bursting stress, and IS0 Recommendation R 391 specifies that
this should be not less than 100 kgf/cm2 [ 10 MN/m2]. An inspection by variables on a sample of 5 pipes will
take into account the 5 values of the unit bursting stress, for example :
110 - 107 - 98 - 103 - 105.
In inspection by attributes it will only be registered that out of 5 pipes submitted to the tests, 4 have been
conforming and 1 non-conforming. In case inspection by variables is possible it is therefore necessary to decide
whether to treat the observation as a variable or to convert it into an attribute. Such a decision must be taken
before sampling and inspection, since the decision must be independent of the actual outcome of the inspection.
Inspection by attributes is simpler to understand, requires less detailed records, and the testing is often cheaper
than the corresponding measurement. In inspection by variables more information is obtained per unit of
product, with the consequence that variables inspection on the average requires a smaller sample than attributes
inspection to obtain the same power of discrimination between lots of good quality and lots of bad quality. TO
be carried out correctly, inspection by variables requires some skill in arithmetic.
Further, the sampling plans for inspection by variables are based on the assumption that the measurements are
normally distributed. (The distribution of Laplace-Gauss). This will generally be the case for the products in
question.
IS0 Recommendation R 390 states that inspection by attributes is normally employed, but the manufacturer
may, prior to the drawing of the sample, opt to employ inspection by variables if applicable.
As far as inspection by variables is concerned the sampling plans given in IS0 Recommendation R 390 are
limited to cases where the relevant IS0 Recommendation specifies either a lower or an upper limit for the
quality characteristic in question.
Therefore, when double limits are specified (for example, for certain geometrical characteristics) i
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.