Stainless Steel

The term “stainless steel” covers a range of steel alloys whose corrosion resistance is based on their chromium content. The chromium contained in the alloy oxidizes and forms a hard, invisible protective surface layer that prevents further corrosion – until the surface is damaged, after which the process is repeated.

Research projects in various countries have shown that austenitic stainless steel, which basically contains 17% chromium and 8% nickel, performs well in common types of soil and has a service life of around 100 years.

However, in poorly drained gravel soils, in the presence of industrial and mining waste and in cases where the soil and groundwater contain chlorides with a concentration of more than 1000 ppm, pitting tends to occur.

For this reason, Fernco offers two different grades of steel. As standard, all steel components used in a coupling are made of austenitic stainless steel to DIN 1.4301 (V2A).

For the harsh environments described above, as well as for special purpose joints, we can also equip our couplings with a steel quality in accordance with DIN 1.4404 (V4A) on request. An increased addition of molybdenum in the alloy improves the corrosion resistance of this steel many times over.

Standard version:
austenitic stainless steel – DIN 1.4301 – AISI 304 – V2A

Special design:
austenitic stainless steel – DIN 1.4404 – AISI 316 – V4A

Elastomer

Our seals are – depending on the DIN-specifications – produced with elastomers according to DIN 681-1 and DIN 681-2.

Mainly the following elastomer-types are used:

EPDM (ethylene propylene diene monomer)
EPDM is a terpolymer elastomer and is a copolymer with a saturated polymer backbone. It has very good ageing resistance, even when exposed to UV and ozone. It is resistant to diluted acids, making it the ideal sealing material for use in civil engineering.

NBR (nitrile butadiene rubber)
NBR is always used when the seal comes into contact with oils and fuels. However, the elastic behaviour of this material deteriorates.
ATTENTION: If you wish to use our NBR couplings for non-wastewater applications, please contact our Technical Sales department. They will tell you whether this seal is suitable for this purpose.

SBR (styrene butadiene rubber)
SBR is one of the best-known synthetic rubbers and has similar properties to NR (Natural Rubber), but loses out significantly in terms of elasticity.

NR (Natural Rubber)
NR essentially consists of polyisoprene and is obtained from the white latex of certain plant species that grow in tropical regions, primarily from the spurge family. It has very good elastic properties, but ages very quickly.

Characteristics

EPDM

NBR

SBR

NR
Ozone resistance excellent adequate adequate adequate
Acid resistance excellent adequate satisfactory satisfactory
Resistance to alkalis excellent adequate satisfactory satisfactory
Electrical resistance good poor good excellent
Impact elasticity satisfactory satisfactory satisfactory good
Elongation at break satisfactory good good excellent
Gas permeability adequate good adequate poor
Oil resistance adequate good poor unsatisfactory
Petrol resistance poor good unsatisfactory unsatisfactory
Temperature window –40 to +120 °C –30 to +100 °C –40 to +80 °C –40 to +80 °C
Short-term peak temperature +160 °C +130 °C +130 °C +130 °C

For most of our couplings we use high-quality EPDM caoutchouc. Essentially there are used nature rubber or synthetic caoutchouc. Our EPDM -mixture contains diffrent additives which ensure the permanent sealing technique that is desired.

By heating the EPDM rubber it gets vulcanized. After this process the rubber is extremely elastic. It is possible to form the material at will without loosing its initial shape.

EPDM is resistant to most of the acids and chemical bases that appear in waste water (detailed inventory list is available). At the same time EPDM resists temperatures up to 160°C. As constant load the temperature is 130°C.