1、TECHNICAL REPORT 7674 Published lW5-02-15 lNTERNATlONALOAGANlZATlON FOR STANOAROlZATlON. MEXAYHAPOAHAR OPl-AHklSAI#lR fl0 CTAHAAPTkl3AUkiM. ORGANISATION INTERNATIONALE DENORMALISATION Performance requirements for plastics pipes and fittings for use in underground drainage and sewage Aptitude B lempl
2、oi des tubes et raccords en mat - type 3, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example). Technical reports are accepted for publication directly by IS0 Council. Technical reports
3、types 1 and 2 are subject to review within three-years of publication, to decide if they ten be transformed into International Standards. Technical reports type 3 do not necessarily have to be reviewed until the data they provide is considered no longer valid or useful. ISO/TR 7074 was prepared by T
4、echnical Committee ISOITC 135, Plastics pipes, fittings and valves for the transport of fluids. The reasons which led to the decision to publish this document in the form of a technical report type 3 are explained in section 1. U DC 621 B43.26 : 626.662.3 Ref. No= ISO/TR 7074-1666 (E) Descriptors :
5、underground sewage disposal, drainpipes, plastics products, plastic tubes, pipe fittings, specifications, tests, test equipment. 0 International Organization for Standardization, 1986 0 Printed in Switzerland ISO/TR 7074-1986 (El SECTION 1 - HISTORICAL BACKGROUND 1. DISCUSSIONS IN IS0 Work within IS
6、O/TC 5/SC 6 (now ISO/TC 138) on a specification for plastics pipes and fittings made of UPVC for use in underground sewage was approved at the sub-committee meeting in Stockholm in 1969 when Working Group A was established and the responsibility for drafting the specification allocated later on to a
7、 Task Group (now ISO/TC 138/SC l/AGH-1 - Buried drain and sewer pipes). At the WG 1 meeting in Berlin in 1972 the U.K. proposed that TG 1 should give consideration to the so-called Box Loading Test (BLT) as described in BS 4660. This was accepted. The “Specification for pipes and fittings of unplast
8、icized polyvinyl chloride (UPVC) for buried drain and sewer pipes“ (dot. 138/l N 161) was forwarded to TC 138 level by resolution in Madrid in 1972 without any functional test requirements for pipes or fittings and at the same time it was decided that TG 1 should continue its specification work on t
9、he quality testing of fittings. - The above mentioned specification, now ISO/DIS accepted with 24 approvals, 2 disapprovals and (see dot 138 N 153). After having finalized the leakproofness tests 4435, was no abstensions for fittings, TG 1 was, by resolution of WG 1 in Bremen in 1974, to continue un
10、der the leadership of Finland developing suitable tests for pipes and fittings. Since then, in the period 1974-1978, nine further Task Group meetings were held keeping in mind the following terms of reference: - To prepare a functional performance test (type test by nature), considering the long ter
11、m durability of fittings, which simulates, as far as possible, practical conditions. - To develop a simple production quality control test, especially for injection moulded drainage fittings, which examines the strength of the weld line, which may be weaker than the the fitting in general. The main
12、task, being derived from the actual initiative, was to study the testing of UPVC assemblies but the AHG has also studied the applicability of the methods established to other plastics materials: no final conclusions have been drawn however. During the work of TG 1 it became evident that no unanimous
13、 proposal could be reached within the TG upon the methods to be used and therefore TG 1 agreed that all prepared descriptions of test methods should be circulated to the WG 1 meeting in Tel Aviv for wider consideration. At the meetings in November 1977 it was agreed that documents 138/l N 369, N 370
14、 and N 371 should be compiled into a Technical Report. ISO/TR 7074-1966 (E) SECTION 2 - BASIC TECHNICAL PROBLEMS 2. INTRODUCTION When flexible plastic pipe is used for underground drainage and sewage, a so-called pipe structure is formed by the interaction of the mechanical properties of the pipe an
15、d the surrounding soil. The behaviour of the pipe structure over a long period depends on the ageing properties of both components, i.e. changes in the pipe or fitting material and variations in the earth pressure distribution cause diminishing pipe strength. The main loading factors, which should b
16、e taken into account when dimensioning the pipe structure are: a) static and dynamic loads which cause bending stresses and fatigue phenomena in the pipe and fitting wall; b) thermal loads which cause accelerated ageing and possible softening in the material and bending stresses in the pipe and fitt
17、ing wall; c) chemical influence of waste water. These factors cause changes of differing degrees in pipe and fitting materials depending on: - dimensions and geometry; - elasticity and stiffness; - creep and relaxation properties; - frozen-in-stresses; - tensile, compressive and fatigue properties;
18、- softening temperature; - molecular weight and its distribution. 3. QUALITY CONTROL PROBLEMS With manufactured products, quality is mainly determined by quality of design and quality of manufacture: - Quality of design is defined as the excellence of the design in relation to ease of manufacture an
19、d to the customers requirements - Quality of manufacture is defined as the fidelity with which the product conforms to the design. When discussing the quality control, which is defined according to the European Organization For Quality Control (EOQC) as a system for programming and coordinating the
20、efforts of the various groups in an organization to maintain or improve quality, at an economical level, we see that the document ISO/TC 138/WG 1 N 299 gives a definition for Quality Control Test that should preferably be called a Production Control Test. The Type Tests and Performance Tests fall un
21、der the heading Quality of design: - The definition of Performance Tests states that they are carried out in order to assess the ability-of a product or assembly of components to fulfill its function - The definition of Type Tests states that they are carried out in order to prove the general suitab
22、ility of materials and components. The question is to which definition should be added the words “over the required time“, which is defined as the period of time (for pipes and fittings normally 50 years) during which the user expects the item to be in a condition to perform its required function. D
23、oes the testing of wear-out or degradation failures belong to both groups. 3 It is clear that in order to get reliable results from a test which simulates functional and environmental stresses the test shall include an accelerating factor. What accelerating means should be chosen is dependent on the
24、 parameters to be investigated. The Task Group has studied the effects of temperature, which is known from previous experience to be a reliable factor, increment of induced stress and dynamic loading. An accelerated test is defined as a test in which the applied stress (loading) level is chosen to e
25、xceed that stated in the reference conditions in order to shorten the time required to observe the stress response of the item, or magnify the response in a given time. To be valid, an accelerated test must not alter the basic modes and/or mechanisms of failure, or their relative prevalence. In orde
26、r to be able to state the reference conditions one should carry out Field Reliability Tests, which are defined as a reliability compliance or determination tests made under stated and controlled conditions of use and recorded conditions of environment in the field. Because results over a 50 years pe
27、riod are not yet available, field data and results from Endurance Tests have been studied by the Task Group. The idealized target of the TG could be crystallized as follows: To establish a simple, easy and quick test, which by simulation takes account of the performance requirements set by the envir
28、onment and the function stresses, reveals inadequate design strength in view of long term durability, which could be used as a reliability test, as a production control test and as a screening.test. A screening test is intended to remove unsatisfactory items or those likely to exhibit early failures
29、. Not surprisingly this proved to be unreasonable and therefore the task Group split the programme into smaller individual Tasks. ISO/TR 7074-1996 (El SECTION 3 - TEST METHODS STUDIED 4. MOTIVE The reason why tests were developed is contained in the sewer pipe specification ISO/DIS 4435. It is state
30、d under the heading “wall thickness“ that “Note: The wall thickness of a given fitting may require greater values than given in the table in order to comply with the test requirements of this specification“. Up to now no guidance has been given within IS0 for the choice of the class of fittings to b
31、e connected to a specific pipe. 5. BOX LOADING TEST (BLT) Originally the work of TG 1, in its present composition, began with a so-called BLT method, which is a Laboratory Reliability Test by nature. The BLT is meant to be a a simulating test which contains thermal shock as an accelerating factor. 5
32、.1 Background The background to the BLT and the objectives it achieves when pipes and fittings are subjected to it lies in the failures of soil stocks reported during 1966 and 1967 in U.K. A number of UPVC soil discharge pipes collapsed due to conveyance of hot discharges. Investigations following t
33、hese failures were carried out by BPF. From this survey two sets of conditions emerged which could have caused the soil systems then in use to fail. These conditions were: a) A rapid discharge of the contents of a boiler. b) The use of washing machines where the temperature of the water can be as hi
34、gh as 95 C. It was subsequently establised that plastics soil systems should undergo an elevated temperature cycling test. The idea was that the test would indicate that when a system satisfactorily performed after the test had been completed then for all practical purposes other pipes and fittings
35、identical to those tested would perform satisfactorily in service. This test is now included in relevant IS0 Draft Interhational Standards for soil and waste discharge systems inside buildings. When the U.K. came to examine the question of drainage pipes from the house to sewer it was immediately th
36、ought necessary for a similar test to be included to determine the performance of these pipes under the influence of thermal shock. However, because the pipes would be buried in the ground and subjected to external loads, additional criteria would be applied. Opinions from building authorities, road
37、 construction specifiers, transportation authorities and organizations were 5 ISO/TR 7074-1986 (El examined and certain load criteria emerged. These load criteria can be said to be the maximum possible normal loadings that would pass over or remain on a buried sewer pipe for a length of time. A simi
38、lar examination with regard to the temperature of the effluent, as carried out for the soil system programme, showed that the effluent conveyed in underground drainage was at a lower and more constant temperature. The practical questions were then raised concerning applying these criteria to a test
39、and it was very quickly seen that to install pipes and fittings in trenches on a continuous basis for test purposes was not practical and an artificial trench had to be designed and specified. Ultimately this artificial trench emerged as the box detailed in the test description which follows this re
40、port. It was considered acceptable for all practical purposes that if the physical properties of the box were toleranced, different laboratories could construct boxes and test components in them to a standard method. This method of determining a pass/fail for the products tested by each group would
41、be satisfactory. As for soil systems, the object of the Box Loading Test is to confirm that pipes and fittings which do not deflect by more than a given percentage during the test, and at the test conclusion show no signs of leaks, will give a satisfactory performance when in use. Again, as with the
42、 soil systems, it is not intended that systems so tested in the box should be given a numerical value whereby systems from one manufacturer can be directly compared with those of another. 5.2 Objections The Task Group studied the original U.K. proposal and the corresponding Finnish standard SFS 3143
43、 - 1975. The main arguments against these methods were: Lack of information concerning a) The weld line quality, because of the small number of test pieces b) The stiffness, because the temperature is as high as 85 C, c) The long term behaviour, because the testing time is short and cannot be suffic
44、iently related to practice d) the method is costly, time consuming and complicated e) The reproducibility is doubtful, 5.3 Progress a) Weld line quality From the investigations made it can be concluded that “frozen-in-stresses“ in injection moulded fittings have a certain effect in relation to the w
45、eld line and thus the weld ISO/TR 7074-1986 (El line can be the weakest part of the fitting. This is evident because when the weld line is placed in the water flow the deformation is often at its maximum-and small cracks in the weld line can be found. Because the method was not originally meant for
46、determining the weld line quality by measuring the depth of the crack and because statistically the number of test specimens is too small, it was agreed that in the standard only a referenc.e for further investigations was to be made in the case of crack development. b) Test temperatures The water t
47、emperature of the hot water cycle was proposed originally as 85 C. This was enough to raise the mean temperature through 60 OC in the material. This in return can cause acceleration of degradation (ageing) failures and thus select bad material quality from good. When resting and cooling the original
48、 test schedule required care to be taken that the crown temperature fell to a maximum of 30 C. This keeps the total assembly temperature at about a constant level. It is interesting to note the relationship of the wall temperature with the long term pressure test for pipes. Experiments made with wat
49、er at 70 C show that the deformations are much smaller. The Task Group discussed the test temperatures on several occasions and studied many reports in which the conclusions were equal: Though the temperature from a washing machine can be as high as 95 C when poured into the soil system, it rapidly decreases and seldom exceeds 60 C when running in the underground drainage system. There are, however, certain types of housing where hot water is discharged into the underground drainage system at a temperature of at least 85 OC. This was concluded from several field measurements. Thus it
