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Elastomer gaskets

Technical solutions

Elastomers

EPDM (Ethylene Propylene) elastomers are normally used for the joint gaskets of PAM potable water and irrigation pipes.
They are rigorously selected on the basis of criteria directed at maintaining their long term physico-chemical properties.

Long term performance

Elastomer ageing

The purpose of elastomers used in jointing systems is to guarantee that the gaskets will be perfectly tight as long as the pipeline is in service. Pipeline experience acquired by PAM has allowed its Research Centre engineers to understand and measure the change in properties with time of various types of elastomers, in order to find the ones with the best performances.

The change in the mechanical properties of elastomers with time can be indicated by two phenomena:
– creep (increasing deformation under constant loading),
– relaxation (compression relaxation under constant deformation).

In the case of socket joints, the seal is obtained by the contact pressure between the metal and gasket. The elastomer deformation produced during jointing remains constant. The relaxation phenomenon is therefore the only one of interest.

Relaxation measurement

Relaxation of elastomers is determined by a procedure which measures the change with time of the force required to compress a specimen of fixed deformation.
The diagram below shows the relaxation at ambient temperature of the EPDM used in the joints of PAM potable water supply and irrigation systems.

It can be seen that:

– the EPDM used by PAM ages less rapidly than a material that exactly meets the requirements of EN 681.1 and ISO 4633,
– long term, the contact pressure remains well above the leakage danger threshold.

Examination of specimens taken from mains after several years’ service has confirmed the excellent long term performance of PAM gaskets: all the physical and chemical properties of the gaskets tested had been maintained after many years of service.

Physico chemical properties

The principal properties of elastomers used by PAM are given in the table below.

Unless otherwise specified, EPDM elastomer gaskets are supplied.
Maximum usage temperature : 50 °C.
Certain storage precautions need to be taken.

PropertiesEPDM (Ethylene
propylene
polymer)
Hardness
range
(Shore A)
40-90
Density (basic product)0.86
Tear
strength
good
Abrasion
resistance
good to excellent
Compression
set resistance
good
Oxidation
resistance
excellent

Specifications and quality management

Specifications

The properties and minimum fitness for purpose requirements for gaskets are standardized.

CriteriaReference Standards
French International
Tensile (strength
and elongation at break)
ISO 37
Creep ISO 815
RelaxationISO 3384
Tear strengthISO 816
Resistance to water
and chemicals
ISO 1817
AgeingISO 188
Resistance
to ozone
ISO 1431-1
Minimal fitness for purpose requirementsISO 4633
EN 681-1

In view of the importance of gaskets in sealing pipe systems, PAM has instituted a more demanding specific quality control procedure, including:

- supplier acceptability, following an evaluation of his ability to supply a product on a regular basis, meeting PAM’s technical requirements, proof of the elastomer suitability,

- acceptance of the manufacturing moulds (design and dimensions),

- checking the quality of prototype gaskets, then of pre-production runs,

- constant monitoring of the supplier’s quality control results and parallel tests in our own laboratories.