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EN 1778:1999

Characteristic values for welded thermoplastics constructions — Determination of allowable stresses and moduli for design of thermoplastics equipment

прийнято як національний стандарт методом підтвердження за позначенням

ДСТУ EN 1778:2019
(EN 1778:1999, IDT)

Нормативні значення показників для зварних конструкцій з термопластів. Визначення допустимих напружень та модулів для проектування виробів з термопластів

ICS 83.080.20; 83.140.01

English version


This European Standard has been prepared by Technical Committee CEN/TC 249, Plastics, the Secretariat of
which is held by IBN.

This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by April 2000, and conflicting national standards shall be withdrawn at the
latest by April 2000.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark,
Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain,
Sweden, Switzerland and the United Kingdom.

Annex A (normative) contains the neccessary creep strength diagrams, the creep modulus diagrams as well as
the reduction factors. In annex В (informative) explanations and calculation examples are included.


Because most components are subjected to multiaxial loading, the creep strength diagrams for pipes are taken
as a basis for the allowable design stresses. The diagrams have been confirmed by results from many years of
measurements and by experience (see [1]).

Extrapolation of creep strength curves to higher temperatures is not permitted. The use of the creep strength
curves for dumbbell tensile test pieces is not correct practice because of the reasons mentioned above.

A large number of reduction factors A2 for the action of the medium taking into account material, stress and
temperature have been included. The reduction factors
A2 for the action of the medium and the weld factors f1
were determined independently of each other.

Investigations established the validity of the multiplicative connection between the weld factor f1 and reduction
A2K(reciprocal value of factor for resistance to chemicals fcRσ (see [2] and [3]).

1 Scope

This standard specifies a methodology for determination of the characteristic values necessary for the design of
welded constructions for example vessels and tanks, ventilation ducting, containers and apparatus.

It is assumed that due regard is paid to the standards and Codes of Practice listed in clause 2 as far as the
choice of materials and their processing are concerned. The data is applicable for static loading.

The relevant EN standards or ISO standards are applicable to the design calculations, dimensions,
construction and testing of the various structures.

This standard applies to a wide range of thermoplastics materials, for example: Polyethylene (PE),
Polypropylene (PP), Polyvinyl Chloride (PVC) and Polyvinylidene Fluoride (PVDF).

Annex A gives minimum properties for specific grades of these materials. The use of other thermoplastics is
permitted, provided that their creep properties exceed the minimum values given in annex A for the known

Properties should be determined in accordance with the relevant ISO and EN standards.

This allows the introduction of thermoplastics with improved properties as appropriate data becomes available.

2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to, or revisions of, any of these publications apply to this standard
only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies.

prEN 12202
Plastics piping systems for hot and cold water - Polypropylene (PP)

ISO 899-2
Plastics - Determination of creep behaviour - Part 2: Flexural creep by three-point-loading

ISO 1167
Thermoplastics pipes for the conveyance of fluids - Resistance to internal pressure - Test method

ISO 8584-1
Thermoplastics pipes for industrial applications under pressure - Determination of the chemical resistance
factor and of the basic stress - Part 1: Polyolefin pipes

ISO/TR 8584-2
Thermoplastics pipes for industrial applications under pressure - Determination of the chemical resistance
factor and of the basic stress - Part 2: Pipes made of halogenated polymers

ISO/TR 9080
Thermoplastics pipes for the transport of fluids - Methods of extrapolation of hydrostatic stress rupture data
to determine the long-term hydrostatic strength of thermoplastics pipe materials

3 Definitions, symbols and abbreviations

K         Creep strength at the design temperature and lifetime in newtons per square millimetres
        Factor of safety
A1        Reduction factor to take account of the effect of specific strength
A2k      Reduction factor taking into account the effect of surrounding medium (reciprocal value of
resistance factor
fcRσ      Stress dependent chemical resistance factor
A2E       Reduction factor taking into account the effect of surrounding medium on the modulus of

EC        Creep modulus at the design condition (temperature, stress, time) in newtons per square

Еc(al.),St Allowable creep modulus at the design condition for stability (temperature, stress, time,
medium, safety factor) in newtons per square millimetres

Еc(al.),D  Allowable creep modulus at the design condition for deformation (temperature, stress, time,
medium) in newtons per square millimetres

         Design temperature in degrees Centigrade
fs         Short-term weld factor
f1         Long-term weld factor
σef       Effective stress in newtons per square millimetres
σal.      Allowable stress at the design condition in newtons per square millimetres
n         Number of fractional loadings
a1,a2..an Proportion of total loading time at each design condition expressed as percent
t1,t2..tn   Service life at the individual working conditions (constant pressure and temperature) taking into
account reduction, joint and safety factors

tx        Design life with or without intermittent loading
σ        Principal stress in newtons per square millimetres

4 Determination of allowable stresses and modul

4.1 General

Design calculations for components are based on long-term values. Depending on the nature of the loading,
there are generally three criteria:

1) Stress;

2) Deformation (e. g. deflection);

3) Stability (e. g. short or long-term buckling).

Stress design calculations shall be made with reference to creep strength, as multiaxial states of stresses are
present in most cases. The maximum principal stress shall not exceed the allowable creep strength.

The allowable values are derived by using reduction factors (see clause 5), a joint factor (see clause 6) and
factors of safety (see clause 7) from the characteristic values of the material.

In terms of deformation and stability, the critical design parameter is creep modulus. This can be obtained from
creep modulus diagrams depending on time, temperature and stress. In the event of stability problems,
allowance shall be made for an appropriate factor of safety (see clause 7).

4.1.1Design calculation according to strength


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