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Last edited 25 Sep 2020
Approved document B of the building regulations suggest that pipes: '...includes pipe fittings and accessories. The definition of ‘pipe’ excludes a flue pipe and a pipe used for ventilating purposes, other than a ventilating pipe for an above-ground drainage
Many different components comprise pipework, including pipes, supports, gaskets, flanges, bolts, valves, strainers, flexible and expansion joints. These are used to sense and control the pressure, flow rate and temperature of the conveyed fluid and the system is usually documented in piping and instrumentation diagrams (P&IDs).
Pipework is commonly manufactured using carbon fibre and stainless steel, although non-metallic and lined or plastic pipework can also be used, including wood, fibreglass, aluminium, copper and concrete. The material selection should consider the variation in process conditions that may occur, such as the change in material strength at elevated temperatures.
When designing pipework, the operation of the system needs to be clearly understood. This means that normal conditions must be assessed, as well as those that arise during start up, shut down and at times of process disruption, which may include the following:
- Pressure surge.
- Condensate-induced water hammer.
- Cyclic loadings.
- Temperature gradients and cycling.
The point of leakage is typically at pipe joints and as a result, the number of joints should be minimised as much as is practicable. Permanent welding of joints can be undertaken for high integrity pipework systems or reformable types used, such as flanged, screwed or compression fittings. It is common for radiography and ultrasonics to be used as a means of assessing high integrity welds.
Safe access for operation, inspection and maintenance should be taken into account when designing pipework routing. Sufficient mechanical strength for the exerted loads should be provided by pipe supports and bridges.
Valves are used to isolate process equipment, both for maintenance and emergency purposes. Careful consideration should be taken, since liquid can be trapped between closed valves and undergo thermal expansion and loss of containment.
A central heating system consists of a boiler, radiators and the pipework which connects them. It is usual for the pipework to be installed below the radiator. With suspended timber floors, the pipes are installed below the floorboards and the risers to radiators passed through drilled holes. To avoid the pipework having to be supported by itself, it should be supported below the floorboards.
Where there are solid floors, high level feed pipes with fall pipes can feed single or adjacent radiators. Alternatively, pipework can be installed between the joists of a suspended ceiling, although if each floor is a separate dwelling this will not be practicable.
Another alternative is to run feed pipes around the top of the wall just below the ceiling with fall pipes. This is preferable to feeding pipes at floor level since doorways create issues, although this can be countered by taking the pipes up over the door or down into the floor.
The basic arrangements for the pipework are as follows:
This involves a single loop of pipework running from and returning to the boiler. As heated water is pumped along the pipe, it rises into the radiator via natural convection, while displacing cooler water back into the pipe.
This is a more efficient system than the single pipe loop, and involves heated water being pumped to one side of each radiator in the system, while the other side is connected to a separate common return pipe. This means that each radiator receives water at more or less the same temperature.
This system uses normal pipework for pumping water from the boiler to manifolds, and back to the boiler. From each manifold, smaller diameter pipework is connected to the radiators, with runs generally kept below 5 m. The benefit of this system is that smaller pipes contain less water, which means less heat is lost along each pipe run.
 Related articles on Designing Buildings Wiki
- Building heating systems.
- Building services.
- Fire collar.
- Grease management.
- How to prevent frozen pipes.
- Mechanical, electrical and plumbing MEP.
- Pipework defects, ventilation and airflow rates.
- Plumbing drawing.
- Pumps and dewatering equipment.
- Sanitary pipework.
- Secondary ventilation stacks in tall buildings.
- Sewer construction.
- Trenchless pipe rehabilitation market.
- Underfloor heating.
- Vertical riser.
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