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Presentation for TC 133, WG 8 Meeting March
8/9th 2005, Cologne LONG-TERM DURABILITY OF SEAL
RINGS for Pressfitting Systems
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Introduction
German Producers
1. LONG-TERM DURABILITY OF SEAL RINGS The seal
rings in press-fitting systems are designed for
hot water applications at temperatures of up to
110C and gas applications at temperatures of
20C to 70 C for an operating period of 50
years. This represents a relatively expansive
load range for the use of seal rings in domestic
systems with a wide variety of temperatures for
gas and water usage from northern Norway to
southern Spain, for example. Statements can be
made about the long-term durability of the seal
rings by means of long-term testing with
extrapolation. Long-term DVR testing was carried
out in de-ionized water at 110 C. This makes it
possible to predict the anticipated service life
of the seals for practical use within the
required temperature range according to testing
periods that go beyond the stipulations of EN
681-1.
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Introduction
2. LONG-TERM DURABILITY OF SEAL RINGS More than
30 years of experience with butyl rubber and more
than 15 years of experience with EPDM is
available. Appropriate long-term proof is
required for new materials that are to be used in
hot and cold water in order to determine their
long-term durability. HNBR materials for
elastomer sealing elements have proven themselves
in gas applications. The optimisation of
standard elastomer recipes for gas and hot water
applications is extremely restricted by differing
requirement profiles on the one hand and positive
raw material lists for drinking water
applications on the other. Much greater long term
durability can be achieved in drinking water and
heating applications with elastomer qualities
that cannot be used for gas applications (e.g.
EPDM, IIR). Quality assurance and product
liability are more important in gas applications
for traceability in the event of disputes. In
spite of meeting the requirements of the current
EN elastomer standards, expensive press-fitting
failures can occur without the knowledge gained
from long-term seal ring testing. A universal
sealing element with adequate durability for
heating water, drinking water and gas
applications still does not exist.
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Introduction

• 3. IDENTITY TESTING DURING CERTIFICATION AND
  MONITORING TESTS
• The requirements and tests for elastomer
  materials are essentially defined by standards.
  
• Elastomer materials can differ by using different
  mixing recipes with different polymers and many
  other constituents (e.g. carbon black, softener,
  antioxidants, anti-ozonants etc.).
• Small quantitative deviations in the
  "vulcanization system", e.g. peroxide/coagent or
  auxiliary processing media etc. can have a
  considerable influence on the process conditions
  and the resulting product (seal).
• For this reason, seal ring identity testing
  during the monitoring test in comparison to the
  initial certification test has important
  significance with regard to quality assurance
• for drinking water applications (EN 681) - TGA
  (thermogravimetric analysis)
• for gas applications in accordance with EN 549,
  Annex B, IR identity testing

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Introduction
4. TESTING OF PLATE MATERIALS AND SEAL RINGS The
process parameters for plate materials and seal
ring materials that comply with the standards
must have comparable vulcanization temperatures
and vulcanization times depending on the product
cross-section and biggest product wall
thickness. If test plates for certification are
vulcanized at a higher temperature for longer
than a seal ring with comparable wall thickness,
better test results can be manufactured
artificaly / synthesised. References that have
been obtained in this way have little to do with
the actual product in spite of mixture identity.
Testing institutes must therefore consistently
pay attention to correspondence of the process
parameters (vulcanization time and temperature)
during the manufacture of test plates and seal
rings. - Seal ring testing
therefore has maximum priority!
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Common elastomer materials for press fittings
Long-term durability can be evaluated by means of
long-term testing of the permanent set and/or the
compressive strain relaxation.
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Compression of the sealing element
Excellent elastomer properties Low compression
set even after 50 years !
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O-ring housing under pressure
1. Diffusion through elastomers (permeation) is
negligible. 2. Sealing Tightness capability of
conventional, permitted connections
Teflon and hemp-sealed
threads and flanged connections
Leakage rate 10 exp 3 to 10 exp 5 (mbar x
l/sec) 3. A O-ring deformation of 15 25 is
standard, see DIN V 65900-17 and DIN 3771-5. 4.
The sealing function of the O-ring is
increased by the inner pressure of the
medium. 5. Experience has shown that
the sealing capability of the connection is
assured up to a compression set of 100 under
practical conditions, O-ring test lab Richter,
annex 3.
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CS of elastomeric seals
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Low temperature functional limit of O-ring
connections

• Leakage abrupt rise of the Helium leakage rate
  at a flat gasket or
• O-ring flange sealing at 1 bar test pressure
• Material T (100 CS) T (leakage)
• C
  C
• FPM 1 -21 -35/-2
• FPM 2 - 7 -20/-2
• FPM 3 -27 -31/-2
• FPM 5 -33 -44/-2
• FPM 7 -33 -41/-2
• FPM 8 -33 -41/-2
• EPDM -47 -61/-2
• MVQ -45 -63/-2
  Compression Set CS
• Source H.P. Weise, H. Kowalewsky, R. Wenz,
  Behaviour of Elastomeric Seals at Low
  Temperature, Bundesanstaltfür Materialforschung
  und -prüfung, Berlin, PATRAM 92, Yokohama 1992
  149-1

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Aging, shrinking as functional limit of O-ring
connections
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compression set of different elastomers