HDPE Pipes

Today one of the most puzzling problems for modern engineers is that of a selection of material construction in order to supply effectively drinking waters to the people. The basic properties material and its cost is one of the determining factors. Any cost of estimation should include the following

• Total material costs
• Labour costs to install
• Savings due to elimination of unscheduled shutdowns or maintenance cost
• Replacement costs
• Life.

Hari Plaast Polyethylene pipes both High Density (HDPE) and Medium Density (MDPE) can carry water, waste water, slurries, chemicals, hazardous wastes, cables and compressed gases as well Polyethylene pipes have a long and successful service experience to the gas, oil, mining and industries. PE pipes have the lowest repair frequency per Kilometer of pipe per year compared with all other pipe materials used for urban water and gas distribution.

Hari Plaast HDPE Pipes are manufactured in sizes from 20mm to 315 mm Outside Diameter in all Classes Pressure Ratings as per IS:4984-1995 & IS-14333-1996. The pipes are available in Coil-Form or Straight Lengths depending on sizes and customer requirements. A complete range of fittings such as Pipe Ends, Bends, Tees, Elbows, Reducers, Flanges are also fall under the range of manufacture.

Economic Pipes and fittings are about 30% cheaper in material cost and 35% cheaper when installation cost are compared.

Light- weight Pipes are extremely light.

Highly flexible Easy installation on uneven contours/unleveled trenches.

Low friction Pipe walls are very smooth resulting in lower frictional losses. Do not permit any bacterial growth or algae.

Chemically inert Immune to corrosion due to any reasons with all chemicals from PH 0 to 14.

Weather resistant Pipes made from HDPE contain non toxic additives like carbon black which safeguards the use in open sunlight & do not pose any problem or stringency regarding their use for potable water supply.

Long life Designed to 50 years trouble free life in all kind of environ- ments.

Water supply Certified by NEERI for potable water transport

Effluent transport Long service life in handling effluents of all kinds.

Chemical transport Can resist corrosion by chemicals from PH 0 to 14. Can safely be used in hostile environments for acids, sludge, D.M.Water.

Gas transport High creep strength PE pipes ideal as gas carriers for Natural gas, Coal gas, LPG etc.

Slurry transport High abrasion resistance together with immune ness to corrosion is an advantage for handling slurry mixture of iron water, Boiler ash water & dredge slurry disposals.

Telecom ducts For use as underground optical fiber conduits.

Irrigation For micro and sprinkler irrigation systems.

HDPE has superb physical & mechanical properties:

Density	0.955 g/cm³
Melt Index	0.2 to 1.10 g/10 min
Tensile Strength at yield point	240 kg/cm²
Elongation at yield point	16%
Elongation at break	> 800%
Ball indentation hardness	480/420 kg/cm²
Shore hardness D	63
Notch Impact strength	9-12 kgcm/cm²
Coefficient of Linear thermal expansion (up to 80ºc)	1.5 to 2.0×10-4cm/cm0C
Heat conductivity up to 20ºc	0.37 K cal/mhc

PERMANENT JOINTS

HDPE pipes can be permanently welded to give a strong and leak proof joint by fusion butt welding process as explained under:

• The pipe faces to be joined should be cut perpendicular to axis and aligned on the welding jacks to ensure close face to face contact
• The pipe faces to be to be thoroughly cleaned by using scrapper blade to remove any oily substances/dirt from the weld faces.
• The weld faces should be brought in contact with the heated mirror after ensuring correct temperature is achieved with help of thermo-chrome chalk. At correct temperature (2100C) the chalk marking will turn blue to black in three seconds.
• Gentle pressure on the pipe will fuse the face material in the form of rim.
• After sufficient (but not excess) fusion, mirror should be removed and pipe faces should be brought in contact under pressure till a fusion butt weld is formed.
• The weld should be cooled in ambient temperature under pressure.
• The weld pressure should be slowly applied to reach maximum of 1.2 kg/cm2 for proper welding.

HDPE pipes cannot not be welded or connected directly with on line valves/utilities. Slip on flanges of matching specification are slid over the pipes. HDPE pipes and end collars are butt-welded to the pipe to form a stopper end and contact face. As the pipe end is also HDPE and hence smooth, flanged joints with a proper gasket do not ooze out leaks.

Fluid flow through HDPE pipes will be governed by the wide known Hazen-Williams equation:

Q = 1002 X C X D^2.63 X S^0.54

Q = Rate of flow, M³ / hr.

D = Pipe Bore, ID in Mtrs.

C = Hazen/Williams constant for HDPE pipe = 150

S = Slop or Hydraulic gradient, mtr/mtr

With smoother wall thickness, HDPE pipe offers very low resistance to fluid flow (C factor = 150) compared to other conventional pipes. The rate of Frictional losses through HDPE pipes could be computed from the friction nomogram provided.

HDPE pipes are highly elastic & can withstand surge pressure up to 1.5 times the Working Pressure rating. Pipes selected should be checked for safety against surge pressure which can be computed from the formula:

Hw = a/g X ∆ V, where,

Hw = surge pressure due to water hammer, M

a = Pressure wave velocity, Mtr/sec.

∆ V = change in flow velocity, Mtr/sec.

Following values of pressure wave velocity should be used for calculating water hammer.

for 2.0 kg/cm2 working Pr. Pipes 173 M/Sec

for 2.5 kg/cm2 working Pr. Pipes 199 M/Sec

for 4.0 kg/cm2 working Pr. Pipes 250 M/Sec

for 6.0 kg/cm2 working Pr. Pipes 305 M/Sec

for 10.0 kg/cm2 working Pr. Pipes 387 M/Sec

The sizing calculations should be checked to ensure that surge pressure does not exceed 1.5 times the working pressure classes.

HDPE pipes can safely be buried underground in all types of soils but shall be protected by100 mm thick sand cushion when laid on to rocks or sharp edges. The permissible burial for all pressure classes of pipes for normal soil loads & under traffic are given below. It is however recommended to lay the pipe through RCC Hume pipes when crossing heavy traffic roads or Railway Tracks.

HDPE pipes can safely be laid over ground or on overhead racks. The pipes should however be firmly supported at very 1.5 M and clamped with due precaution that no sharp edges come in contact with the pipe surface.

A high rate of linear expansion in exposed pipe section can be expected. The usual rate of expansion/contraction is 0.20 mm per C per running meter. It is therefore, suggested that thermal expansion should be taken care of by providing Rubber expansion bellows/joints at fairly close intervals.