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Durability and Resistance

Durability and resistance of Flexseal Couplings

Flexseal couplings are manufactured for use when jointing pipes in sewerage, drainage and other non-pressure applications. They consist of an elastomeric sleeve with clamping bands. The clamp bands are manufactured from stainless steel. The sleeve is normally supplied in EPDM material but, where resistance to hydrocarbon contamination of effluent is required, Nitrile seals are offered.

The product is manufactured to the requirements of BS EN 295. This has a requirement for the elastomeric seal to be compliant with BS EN 681 Part 1.

We have to consider three aspects concerning the durability of the product.

  1. The life of the elastomeric sleeve.
  2. The life of the stainless steel clamp bands.
  3. The performance of the product.


1)    The durability of the elastomer is influenced by many factors such as the type of elastomer, the temperature and the environment in which the elastomer is functioning.

EPDM Couplings

EPDM has good or excellent resistance to oxidation, ozone, ultra-violet light and heat. This property makes the elastomer suitable for both underground and above ground applications

The product is manufactured for use in drains and sewers. Any substance not usually associated with this application could possibly be detrimental to the elastomer. In such cases advice should be sought about the suitability of the elastomer to resist chemical attack. EPDM is not suitable for effluent contaminated by hydrocarbons. In these cases, Nitrile seals should be used.

We state that our product is suitable for normal drain or sewer operation at a continuous temperature of no more than 80°C and an intermittent temperature of 100°C. It should be noted that EPDM has a quoted operating temperature range up to 150°C and our recommended maximum temperature is listed to consider product longevity.

Nitrile Couplings

Nitrile should be used when effluent is contaminated by hydrocarbons in below ground applications. In this environment Nitrile will provide a long service life. The nitrile compound used with Flexseal couplings is not suitable for use in pipelines carrying hydrocarbon liquids of high concentrations.

Nitrile compounds have a quoted operating temperature range up to 120°C.  We recommend that our Nitrile couplings should not be used for continuous operating temperatures in excess of 45°C to ensure product longevity. It is considered unlikely that applications requiring Nitrile as the elastomer will operate at temperatures higher than ambient conditions.

2)    Stainless steel usually has excellent durability. It can be attacked by chloride ions present in soils by the mechanism of crevice corrosion. If this is anticipated to be a problem then the higher grade 316 stainless steel should be utilized.

3)    The performance of the Flexseal product is dependant upon maintaining contact pressure under the clamp band to ensure the seal remains tight. The elastomer has to meet performance criteria specified in BS EN 681:1. This factor ensures that the physical properties of the material are both known and consistent. Extrapolation of the results of stress relaxation under compression provides a figure for 50 year relaxation. Our clamp bands can exert sufficient clamping pressure at the recommended tightening torque to ensure that there is adequate contact pressure even after 50 years of stress relaxation.

We are confident that these products, if correctly specified and installed, are adequate for a 50 year life in below ground applications.