Durability

Pipe system components must withstand hazards before they reach the job site such as accidental impact before and during installation, during storage, handling and transit.

In service, outdoor exposed pipes may be damaged by accidental impacts or vandalism. To avoid breakages, which can be expensive, or minor stress cracks which can have serious consequences in operation, the choice of material should be carefully considered.

Impact strength and crush resistance

Compared with other materials, cast iron provides much better impact resistance and is highly recommended everywhere pipes may be exposed to mechanical shock (car parks, streets, etc.).

Cast iron is well known for its robustness. The quality of PAM Building products is ensured by careful control of both the metal composition and the manufacturing process. The spinning of pipes in the De Lavaud process, followed by heat treatment, gives these products outstanding mechanical properties.

The advantages of the De Lavaud process: better mechanical characteristics, superior to the requirements of EN 877*

• Very good resistance to crushing.
• Increased impact resistance.
• The pipe is more resistant to mechanical stress such as bending and compression.
• For installers, installation is more comfortable and on-site handling is facilitated. Cutting pipes is easier, the slices are sharp. The set-up is therefore simpler and faster.

These results indicate greater resistance to impacts and crushing, easier machining and cutting. This also means the products are easier to install on job sites.

*Key mechanical characteristics required by standard EN 877 are checked by three tests, carried out on pipes when coming out of the heat treatment furnace to assess tensile strength, ring crush resistance and hardness. In addition, operators have opted to perform a further test which provides a good indication of the heat treatment quality: impact test.

Thermal expansion coefficient of cast iron and other materials

The thermal expansion coefficient for cast iron – 0.01 mm/m. °C – is very low and very similar to that of steel and concrete; the building and pipe systems will move and expand together.

For cast iron, the bracketing system is designed to only carry the weight of the pipe and its content, which makes the designers’ work easier. Plastic pipes, however, expand considerably with increasing temperature.

Their bracketing system must be designed and adapted accordingly, as it can significantly affect the pipework’s stability and performance over time.

Thermal expansion of plastics

To allow expansion without damaging the drainage network, plastic pipe systems require specific accessories – expansion collars or joints, brackets allowing axial movement, in general one of the two. If these precautions were not taken, expansion could be absorbed by the pipework and cause distortion.

Cast iron does not require these expensive accessories. It makes the design work easier and decreases the risk of mistakes at the installation stage.

These properties of cast iron pipe systems are also valuable for engineering structures such as bridges, where significant expansions have to be carefully addressed to secure the construction project.

Sanitary drainage systems, whether exposed or not, must remain watertight over time. Any defects can cause serious damage, leaks, dripping or slow permeation and generate costly repairs, and disruption. PAM Building cast iron mechanical assemblies are designed to easily achieve instant watertightness and are not dependent on process control (gluing or welding, etc.).

Watertightness and maintenance

Blockages can sometimes occur in drainage networks, therefore the pipework materials must be resistant so that maintenance is easy. The S and Plus systems can withstand all normal maintenance processes, including high-pressure jetting, without being damaged. They have undergone a high-pressure test according to Swiss standard SN 592 012.

The robustness and dimensional stability of cast iron components along with the careful selection of elastomer ensure pipe installations are high-performance and have a long service life.

Internal overpressure in drainage networks rarely occurs and is always accidental. Thrust efforts in the overloaded sections have to be addressed to guarantee both watertightnessand mechanical stability.

As the robust cast iron components can withstand any pressure hazard, the couplings will be subjected to the strain. The quality of the couplings and their careful selection according to their field of use will prevent misalignment or disconnection of the pipework.

As components that are integrated in buildings, wastewater and rainwater drainage systems must remain in a serviceable condition over the long term despite adverse operating conditions.

Ageing refers to any gradual, irreversible change in a material’s structure and/or composition, liable to affect its behavior or serviceability.

When a material is selected, the stability of its properties ensures operational reliability over time.

Deterioration of mechanical properties under temperature stress

Under the effect of temperature, plastics can suffer two kinds of deterioration, including at operating temperatures:

• Creeping is an irreversible elongation under the combined action of both temperature and a significant mechanical strain. Plastic pipe systems like PVC or HDPE are particularly sensitive; in the horizontal sections, they can bend between two support brackets under their own weight.
• Modification of the elastic limit: most plastic materials will soften when exposed to a temperature increase. With a decrease in temperature, however, they crystallise. PVC, for example, becomes rigid and may crack under mechanical strain - its operating temperature range is generally between -20°C and 80°C, but depending on its nature, the range can be much narrower.

Photochemical ageing

Depending on their nature, climatic stresses (such as solar radiation, damp or heat) will cause photochemical ageing to plastic materials of varying severity.
They may merely alter their surface finish, or they may also deeply modify their mechanical properties and thus adversely affect their serviceability.

The same can happen as a result of a slow chemical attack by solvents or even in an aqueous medium.