Installation
8. Assembly
oval shape. Oval pipes create extra work when welding joints. Bear in mind that pipes can get very hot in the sun. Once out of the sun they will shrink again. If the pipe is at 70°C and the temperature inside is 20°C, a 5 metre long HDPE pipe will be 0.2 x 50 x 5 = 50 mm shorter. Leave accessories in the packaging as long as possible. HDPE electro-weld sleeves should be stored indoors and left as long as possible in the packaging to prevent oxidation from sunlight. Oxidation on the interior can badly affect welds. 8.1.4 Oval pipe ends Excessively oval shape HDPE pipe ends should first be made rounder. This can be done by clamping the pipe with one or two brackets with one or two pieces of padding between, placed a little back from the eventual coupling insertion depth at the end of the pipe. The brackets are only removed after the weld has cooled. 8.1.5 Shortening pipes The best and simplest method is to use a proper pipe cutter. The cut is then straight and no burrs are generally created. If a saw is used, care needs to be taken to ensure that the cut is straight: mark the cut, use a stiff saw blade and use a saw horse with Ø above 50 mm. Remove internal and external burrs with steel wool or a knife. For sawing HDPE use a fairly coarse-toothed blade with a wide set. 8.2 Joints Joints fall in principle into two categories, those resistant to tension and those not resistant to tension. Welded and flanged joints are resistant to tension. Expansion sockets and connections using rubber seals are not resistant to tension. 8.2.2 Joints in HDPE HDPE pipes can not be joined using solvent cement as PVC can. However welding of HDPE gives excellent results. This creates a
tension-resistant connection. There are two methods of welding: hot plate welding and electro-welding using fittings with integral heating elements. Flange joints are also resistant to tension, but this technique is very rarely used in above-ground drainage work. Rubber O-ring joints are found in insertion couplings and expansion sockets in HDPE.
As well as the design of the installation there is also the actual assembly. The design is complete, but many decisions remain to be taken by the fitter which will impact on the quality of the work and the problem-free operation of the waste removal system.
In order to calculate the external over- pressure in kPa the height in metres of liquid concrete must be multiplied by 24. If the pipe is filled with water to counteract flotation the multiplication factor is 14. Example: 6 metres of liquid concrete, pipe Ø 110 mm without water filling, pressure 6 x 24 = 144 kPa. Minimum required for HDPE: 110 x 34. With water filling the external overpres- sure is 6 x 14 = 84 kPa. In HDPE SDR 26 will suffice.
Length threaded
Pipe diameter
Illus. 7.12 Required threaded leg diameter for a given pipe diameter, and maximum bracket leg length for fixed point brackets with rigid installation in HDPE waste removal system. bracket leg mm 40 50 63 75 90 110 125 160 200 100 1 /2 ” 1 /2 ” 3 /4 ” 3 /4 ” 3 /4 ” 1” 1 1 /4 ” 1 1 /4 ” 1 1 /4 ” 150 3 /4 ” 3 /4 ” 1” 1” 1” 1 1 /4 ” 1 1 /4 ” 1 1 /2 ” 1 1 /2 ” 200 3 /4 ” 1” 1” 1” 1” 1 1 /4 ” 1 1 /2 ” 2” 2” 250 1” 1” 1” 1 1 /4 ” 1 1 /4 ” 1 1 /2 ” 2” 2” 2” 300 1” 1” 1 1 /4 ” 1 1 /4 ” 1 1 /4 ” 2” 2” - - 350 1” 1 1 /4 ” 1 1 /4 ” 1 1 /4 ” 1 1 /2 ” 2” 2” - -
8.1 General
8.1.1 Pipework in the waste removal system The pipework must be installed with a particular fall as indicated on the drawings using brackets, bands and supports. They must not be fitted horizontally, but there must not be too great a fall. Excessive fall leads to the complete closure of the pipe and to poor ventilation. Where reducing pieces are used the top of the pipework should be at the same level. The desired installation method must be known (see 7.2).
Butt welding Both pipe ends are placed against a hot plate at a constant temperature and pressure. The plastic pipe ends are now pressed together so that the molecules of the material are transferred between them. Wavin HDPE pipes and accessories can be hot plate welded with good results. Hot plate welding creates small ridges inside and outside the pipe. It is recommended that a training course should be followed. Before starting with hot plate welding the equipment should be checked over. - The hot plate temperature should be 210° C. - The hot plate must be clean and free of grease; clean as necessary with a clean cloth and alcohol. - Ensure that the two pipe brackets
8.1.2 Brackets All types can be used with support
Illus. 7.13 Bracket for casting-in HDPE in concrete.
brackets; from light nylon band brackets, light or heavy PVC brackets to galvanised sewer brackets, and suspension bands. Ensure that any sliding brackets do actually slide (avoid over-tightening). Brackets used for clamping must be strong. For fixed point brackets (only with HDPE) galvanised steel brackets must be used. 8.1.3 Storage Rubber O-rings must be kept in a cool and dark place and not exposed to sunlight (not even behind glass). Pipes must be stored as flat as possible to prevent sagging. It is difficult to produce neat, straight work with bent pipes. Keep pipes as clean as possible; this saves time when preparing and making connections. Covering is recommended during extended storage outdoors. Ensure that HDPE pipes, and particularly the ends, do not take on an
HDPE
calculated resistance
SDR HDPE
Du/e pipe size
(kPa)
13,3 40x3
635
50x3;
63x3,6;
75x4,3
17 90x5,1;
110x6,3; 125x7,1
348
160x9,1;
200x11,4
21 63x3
178
75x3;
90x3,5; 160x6,2;
110x4,3
26 125x4,9;
92
200x7,7
and the two pipe supports are correctly aligned. This can be
30 90x3
58
32 110x3,5;
125x3,9; 200x6,2
50
achieved by clamping 1 section of pipe in both clamps and both pipe supports. If necessary adjust the two pipe supports until they are correctly aligned with the pipe. - Both pipe clamps must be adjusted so that they hold the pipe tightly
160x5,0;
Illus. 7.14 Resistance to underpressure (=external
overpressure) of HDPE pipes at a mean wall temperature of 30°C.
30
31
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