Noise
6. Casting in heat cured concrete and extrusion shrinkage
Butt welding creates ridges on the interior and exterior of the pipe. The internal ridges can hinder the proper flow of foul water. An experienced welder will be able to make a sound welded joint with only minimal ridging. Electro-welded sleeves can be applied in critical situations. 7.1.2 Brackets Brackets must have sufficient strength to carry the weight of the complete pipe- work when full. Illustration 7.1 shows the suspension forces for filled HDPE pipework for various bracket separations. Brackets may have different functions: support, clamping or fixing. A support bracket serves to carry the weight of the pipe- work. If the pipework expands or shrinks it must be able to slide through the bracket (or the bracket must be able to follow the movement with little resistance, for example through the use of a long, slender suspension leg which will easily bend). Clamping brackets serve to fix the pipe with respect to the structure. The bracket must therefore hold the pipe securely and be attached to the structure limits are set down in the standards against set temperatures, and are for HDPE: at 110°C max. 3%. The pipe will expand during heating of the liquid concrete. The degree of expan- sion is limited as the pipework is fixed at various points and (the mass of) the concrete restricts expansion. Once the concrete has hardened the pipe will shrink due to thermal shrinkage and extrusion shrinkage. This is resisted by the hardened concrete as the pipework is held fast by bends, sleeves, T-pieces and similar, so that tensile forces arise in the pipe. The tensile forces give rise to con- centrations of stress which may lead to breakage. T-pieces are particularly susceptible to stress concentrations.
HDPE pipework gives excellent results when cast into concrete floors and walls (see Chapter 7, Installation). Concrete is sometimes brought to very high tempera- tures in order to allow shuttering to be struck the following day, particularly in tunnelling work. The temperature gauge controlling the burners may sometimes be defective. It is also sometimes the case that the control of the burners is carried out using the outermost tunnel sections, because these cool most rapid- ly. The temperature in the enclosed tunnel may then be appreciably higher. Extrusion shrinkage becomes significant for plastic
without excessive deflection. This method allows any changes in length to be transferred to places where these can be dealt with by means of bends, flexible pipe, expansion sleeves and so on. With HDPE pipework systems the pipes can be fixed so that no changes in length can occur. The forces generated can be taken up by the pipe- work itself and transferred to the structure via fixed point brackets. We then talk about "rigid installation" with fixed point brackets. Rigidly installed pipework has a tendency to undulate. This can be prevented with the use of rails or bearers (see 7.2.2). The degree of extrusion shrinkage depends on the maximum temperature achieved. It is clear that the temperature of the pipes may be no higher than 80 to 90°C to cut out all risk. Since the variation in temperature in the concrete can be fairly great, it is stipulated that the measured temperature shall be no higher than 50 to 60°C. Higher temperatures are in any case not good for the quality of the concrete. HDPE pipes for above-ground drainage are sometimes "tempered" for safety reasons. That means that they are heat treated during or following manufacture (extrusion), largely removing extrusion shrinkage.
5.3 Noise reducing measures 1. Waste pipework should not be located in the vicinity of occupied areas, and must never be led openly through occupied areas. 2. Good routing and ventilation cut down noise generation: Falling waste water should be led down smoothly in stages, abrupt descents are bad from a noise point of view. At the foot of the stack a calming section of 250 mm should be used at the transition from the stack to the horizontal pipework. The use of 2 bends of 45° with long legs is recommended here. Waste pipework should be dimensio- ned so that air can circulate freely along with the waste water. A gradually tapered reducer creates less noise than an inserted reducer does. Connections to collecting pipework or to underground pipes should prefera- bly be by means of side connections. Where top connection is unavoidable, then an angle should be employed. At the foot of the stack the axis of the horizontal pipe can be shifted around 1 x D with respect to the axis of the stack. This allows the water to cling better to the walls creating less noise. 3. A plastic pipe wall is and remains smooth so that flows are not disturbed. 4. The special ASTOLAN® pipe wall (Wavin AS) prevents airborne noise and contact noise. 5. The Wavin AS expansion compensa- tor prevents transmission of contact noise. 6. A rubber insert in the brackets prevents transmission to the wall, pipework must never make contact with walls or other materials.
5.4 Fittings Noise from fittings can be limited by:
7. Fixing to a heavy wall damps down contact noise (preferably > 220 kg/m 2 ). 8. No brackets should be located in impact zones. 9. A (heavy) intervening wall damps down transmission by air. 10. With dummy wall constructions the pipework should be secured to the bearing wall rather than to the dummy wall. 11. All wall and ceiling penetrations should be provided with rockwool or other elastic materials. This prevents direct contact between the pipework and the wall and the transmission of airborne noise from one room to another along the pipework. 12. Where a pipe duct is present, the inside of the duct wall must be provided with absorbent material (mineral wool). 13. With horizontal pipework below a false ceiling, provide extra insulation with lead foil at bends and connec- tions. Since the method of installation affects the generation of noise it is recommen- ded that the installation is carried out by well-trained fitters. Where the measures outlined above are implemented consistently, no additional noise insulation will generally be required.
anti-vibration insulation and anti-vibra- tion fixing of the toilet pan removal of reverberation by placing damping material below baths and shower trays reduce noise from water jets by using a small angle against the wall or by means of a perlator.
pipework in these circumstances. Extrusion shrinkage is the single-
occurrence shrinkage measurable when the pipe is heated and then cooled. The
7. Installation
The installation of waste pipework can be divided into the installation design and the installation itself with the actual work of fitting. The installation must be such that the pipework system can fulfil its function without problems and with the minimum of maintenance. The system must be able to handle changes in use, such as changes to the frequency of discharges or the temperature of the medium. The most important condition is that the system must be able to with- stand the loading generated in installation and use. These include: loading through the contents and the weight of the pipework itself; flotation forces when casting into concrete floors and in some cases with underground pipework; forces arising from changes in length due to fluctuations in temperature. This imposes a number of requirements on the design and installation of the system. 7.1 Design 7.1.1 Fixings Welded connections in HDPE may be either butt welds or electro-welded sleeves.
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