What is the use of FRE Duct in Optical Network?

Use of FRE Duct in Optical Network : In this article I will try to covers the minimum standards and requirements for Fiber-Class Reinforced epoxy FRE duct and fittings to be used in the telecommunications network. In this article, we will discuss why and where a FRE duct is used in optical network.And how FRE duct is important in an optical network.

The "Fiber-glass Reinforced Epoxy Duct" FRE Duct is used to provide an installation facility for telephone cables, where extra strength and less flexible is required, such as for road crossings and bridge structures. FRE duct may not be used in some countries but telecom friends should know about it.

Fiber-glass Reinforced Epoxy Duct

FRE duct in optical network

FRE Duct Materials

FRE duct consists of Fiberglass reinforced epoxy with a minimum glass content of 65 %, a barcol Hardness of 52 ± 2 and a specific gravity of 1.94 ± 6. The glass fibers used in the production of the fiberglass duct shall be of a minimum continuous length of 10 meters.

The resin used shall be a thermo set epoxy or polyester of minimum tensile strength of 40 MPa. The glass-resin composite shall have a minimum tensile strength of I00 MPa.

The resin shall have sufficient ultra-violet light inhibitor to render the composite material unaffected by the sunlight. The UV inhibitor shall be added to the material used for duct and fittings, such that one year of unprotected storage shall not degrade the quality of the material. After one year of unprotected storage, the duct and fittings shall be able to pass all the tests.

All materials used in the manufacture of the duct and fittings shall be new material; and shall not contain any fillers, plasticizers, or additives which may react harmfully with polyethylene or lead sheathed cables.

No constituent material shall be used which will adversely affect the Long term mechanical strength of the FRE Duct. All constituents shall be uniformly and fully dispersed.

Ducts and all fittings shall be homogeneous throughout. The internal surfaces shall be clean, smooth, uniform in color, and without any visible cracks, grooves, blisters, wrinkles, dents, heat marks, delimitation or foreign matter inclusions. Ends shall be square, free from sharp edges and exposed fibers.

A clean, squared surface shall be obtained when a duct is cut with a handsaw. There shall not be any cracking or crumbling of the duct surface or edge.

FRE Duct Design Requirements

All couplings, bends and sleeves shall be capable of passing a ball of 100 mm diameter.The ducts shall not exceed a weight of 1.5 kg/m. Ducts shall have a static coefficient of friction between a glycerin Lubricated polyethylene sheathed cable of Less than 0.3 or a static coefficient of friction of less than 0.2.

The maximum roughness on the inside of the duct shall be 125 micro-inches. The load required for duct failure due to wall collapse shall exceed 5000 Kg/m. The load required for failure due to wall collapse of~ the fittings shall exceed 2000 Kg/m of duct. 

FRE Duct Operational Requirements

The design of the duct shall allow for ease of system installation and the ducts shall be interchangeable. The mating surfaces of the couplings, bends, sleeves, duct etc, shall be such that a workable, tight fit between the sections shall be achieved.

The joining of two ducts shall provide a water tight joint. The ducts shall be easy to cut with a saw, to file and to shape. Cable sheaths shall not bind or bond to the duct, during the lifetime of the installation. 

The ducts shall have working temperature range between -20°C to +80°C. The packaged ducts and fittings shall withstand external storage exposure for at least 12 months without significant deterioration of the ducts or fittings.

FRE Duct Testing

Impact Test: The duct and fittings shall be tested for impact resistance according to the methods provided by industry, the specimen length shall be I50 mm. The falling weight shall be a 5 kg. or 10 kg. The minimum impact resistance shall be 10 kg m.

The specimen shall be considered as having failed, when a crack or split is created on the inside or outside of the specimen.

Compression Tests - Failure by wall collapse: A 1 m. section of duct shall fail due to wall collapse at a load exceeding 5000 Kg per meter of duct; and the fittings shall fail due to wall collapse at a load exceeding 2000 Kg per meter of duct.

Compression test - Diameter deformation - I0 % : A one meter section of duct shall be cut and placed between two parallel steel plates, and compressed at the rate of 12.5 _+ 0.5mm/min until the inside diameter of the specimen has been reduced by 10 % . The minimum force required to obtain this deformation shall be 800 kg.

Deflection Testing: Two sections of duct, each 1m ± 10mm long shall be assembled (with bell and spigot joint as supplied by the manufacturer) with three light hammer blows on one end. The assembly shall be supported on two supports Im ± 10mm apart, with the joint located in the middle ± 25mm of the span.

A weight of 2 kg ± 5g shall be suspended form the middle of the joint and the maximum deflection of the assembly shall not exceed 5mm.

Water Absorption: All ducts and fittings shall not absorption more than 0.2 % of water by weight. 10 Specimens 100 mm. in length shall be carefully weighed to the nearest 0.1 gm.

The specimens shall then be completely immersed in tap water for 72 hours at 20°C +2°C. The specimens shall be removed from the water, and the surface water quickly and carefully wiped off.

Within 3 minutes of removal from the tap water, the specimens shall be weighed again to the nearest 0.1 gm.

The average percent water absorption shall be calculated on the following basis:

weight wet - weight dry x 100 = % absorption

           weight dry

The average absorption of the specimens shall be less than 0.2 % with no result higher than 0.5 %.

Ignition Test: The average residue from the test shall be not less than 65 % and the minimum residue of any one sample shall be not Less than 60 %. 

Chemical Resistance: 

- Hydrochloric Acid HCI 5% Solution

- Sulphuric Acid H2 SO4 5% Solution

- Calcium Hydroxide Ca(OH) 2 0.2% Solution

- Sodium Carbonate NaCO3 5% Solution

- Nitric Acid HN O3 5% Solution

- Gasoline 90 Octane

- Lubricating oil Commerical grade

- Diesel oil Commercial grade

The above solutions are to be used at 20°°C ± 2 °°C .Samples of 12.5 mm ± 0.5 mm width shall be used determine the tensile strength before and after chemical immersion.

All FRE Duct products shall be able to withstand a 30 days immersion in the solutions Listed above. After immersion there shall not be any signs of softening, or disintegration, nor a change in tensile strength of greater than 5 %.

Thermal Expansion Coefficient: Coefficient of thermal expansion shall not exceed 2.5 x 10-4 mm /m /°C.

Ultraviolet Degradation: The ducts shall withstand exposure to 15 cycles in the Atlas Weather -0- Meter or equivalent. without losing any impact resistance. Each cycle shall consist of 24 hrs. of ultraviolet (UV) exposure.

Joint Engagement Test: Using a suitable test method (at 20°C ± 2°C), the fit between duct and .fittings, shall be such that 10.2 joules maximum of energy shall cause a full engagement of the mating surfaces (bell to spigot). Also, in a reverse loading, 1.4 joules minimum of energy shall cause a complete disengagement of the mating surfaces.

FRE Duct Identification and Packing

All 6 m sections of FRE duct shall be clearly marked at 1.5m intervals (that is, 3 times on each 6 m. Length) with the following information in English.

⇾Duct, FRE
⇾Manufacturer's Name or Trademark
⇾Month and year of manufacture.

The marking shall be done in a white or black color.. The marking shall produce a permanent inscription on the duct without any notching.The FRE duct may be crated or supplied as loose lengths.

The fittings shall be packaged in such a way to protect them from damage during shipping by land or sea, and during storage. All fittings packaged for manual handling may be multipacked to a maximum weight of 25 kg.

FRE Duct fittings specification

The FRE Duct fittings described in this specification are as follows-

Bend (90° - 1500 mm R)
Bend (45° - 1500 mm R)
Bend (90° - 900 mm R)
Bend (45° - 900 mm R)

End Cap:

Double Bell Coupling (0°)
Double Bell Coupling (5°)
Bell End Fitting
Sleeve

➤The Bend (90° - 1500 mm.R) and (90° - 900 mm.R) is used to provide a 90° directional change to the duct run.
➤The Bend (45° - 1500 mm.R) and (45° - 900 mm.R) is used to provide a 45° directional change to the duct run.
➤The End Cap is used to seal the end of the duct to prevent the ingress of water and debris.
➤The Double Bell Coupling (0°) is used to connect two spigot ended ducts straight through.
➤The Double Bell Coupling (5°) is used to connect two spigot ended ducts and also to provide a 5° directional change to the duct run.
➤The Bell End Fitting is used to provide a smooth cable entry through manhole walls etc.
➤The Sleeve is used to provide a connection between the spigot of an FRE duct with the spigot end of a PVC, FRE or other duct of 100 mm. nominal diameter.

FRE Duct Dimensions 

The FRE duct sections shall be provided with the following dimensions-

Outside diameter.......……………………………… 106 mm + 2, - 0 mm.
Wall thickness .......……………………………… .2.3 mm + 0.5, -0 mm.
Effective Length....:..:………………………… ……6000 mm + 100, 0 mm.

Each 6000 mm section of duct shall be provided with bell and spigot end shall be chamfered to produce a 15 °beveled edge along the outer circumference. The bell end shall be preformed into a plain bell socket suitable for coupling with the chamfered spigot end of an adjacent.

The duct shall be provided with a round cross-section. The maximum permissible out-of-roundness shall be 2% for any cross-section. The eccentricities shall be measured by comparing inside diameters or. outside diameters.

The duct shall be straight longitudinally. The maximum permissible straightness deviation shall be 50 mm. for a 6000 mm section of duct.

FRE Duct Bends

Bends detail in RFE Duct

RFE Duct Bends

The bends shall be provided with bell and spigot ends; and they shall have a 150 mm. straight extension on the ends; and the spigot end shall be chamfered to produce a 15° beveled edge along the outer circumference.

The 90° bends shall bear a mark where they can be cut into two equivalent 45° bends.

End Cap: The End Cap shall be provided with an inside taper to mate with the spigot end of the FRE duct and with the dimensions.

Coupling: The couplings shall be provided with the dimensions Double bell coupling (0 °) and Double bell coupling (5 °).

Bell End: The bell and Fitting shall be provided with an inside taper to mate with the spigot end of the FRE duct.

Sleeve: The sleeve shall have an inside diameter such that it will fit over the 110 mm outside diameter of the duct.

Last Word

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