Piping design: which pipe for what purpose?

First manufactured in 1864, cast iron pipes have stood test of time as the material of preference for drainage systems. Choosing the right material calls for an objective understanding of the conditions, strengths, and weaknesses of each material. 

What are the benefits of Cast iron pipes ? 

Cast iron pipe systems have the robustness and strength that other materials cannot match. Cast iron systems typically last the lifetime of a building, making them an ideal solution for main soil and rainwater stacks. 

Cast iron is resistant to thermal expansion and contraction which means there is no need for expansion joints on the system.

Independent laboratory tests carried out by independent third parties such as IBP (Germany) and CSTB (France) have records proving that cast iron systems are quieter than any other material systems when water flows through them. 

In high-occupancy and multi-storey buildings, cast iron systems are the best alternative:

  • they will not add to the spread of the fire across floors
  • they will remain structurally sound far longer
  • They will barely emit any smoke or fumes, considered as the fastest killer in case of a fire.

This is a vital consideration for multi-storey residential buildings where fires could break out while occupants are sleeping, increasing the risk of injury or death.

They are also an ideal choice for buildings where mobility of the occupants is limited, such as in hospitals, areas of public gathering and assembly, and correctional service centres.

What considerations do the plumber need to be aware of?

Modern cast iron systems made to EN877 are lighter-weight and user friendly. Epoxy coated fittings are also cleaner to handle, and designed to deal with the demands of modern drainage needs.

The plumber needs to understand the latest jointing options available for cast iron systems. These include stainless steel mechanical couplings and push-fit options which are quicker and easier to assemble, making the water-tightness easy to achieve.  Mechanical couplings for pressure requirements in excess of 5 bar and bracketry to suit applications are also available in the market.

The plumber should be aware that with cast iron drainage systems there is no additional requirement for extras such as fire protection and collars, acoustic wrapping, and expansion joint.

What installation mistakes can installers avoid?

Installing a cast-iron system is simple, with less room for error. However, certain areas of common mistakes still exist. A common installation mistake is not allowing the right gradient in the horizontal system which can cause areas of “ponding”.

  • The recommended tools for cutting cast is a common hacksaw using a diamond/tungsten tipped disc. 
  • Although cast iron pipes are easy  to assemble, they require proper positioning before bolts are tightened. Failure to assemble correctly usually results in problems during air-testing of the system before sign-off. Installers need to adhere to assembly instructions as provided by manufacturers. Alternatively to further simplify installation and reduce installation time, cast-iron push-fit systems can be used. 
  • System Restraining is not always correctly done, regardless of particular system material type; particularly where the system is required to cope with any pressure where a change in direction occurs. Cast iron pipes and fittings manufactured to EN 877 are able to handle pressure in excess of 5 bar if correctly restrained (i.e. appropriately bracketed); with the exception of the push-fit system which has been tested to not exceed 1.5 bar.  Use of manufacturer brackets as recommended is not always adhered to - which can put the entire network at risk.

The superior mechanical and “fit and forget” or longevity properties, combined with non-combustibility and superior acoustic properties make cast iron an ideal choice. Cast-iron systems are best used in multi-storey buildings, high-occupancy structures, and mixed-use developments. Masemola Lefentse, Saint-Gobain PAM 

How is cast iron priced?

Cast iron is generally perceived to be more expensive than plastic pipe systems.

However, different plastic and alternative material systems are also priced differently. It can be argued that the cost of a system should be considered “installed”, meaning the total installed cost (including time, labour, and additional components for required system performance to name a few); and not on a system item/ component basis.  

For building owners, there is a longer term cost consideration: how much will the system cost me over its entire lifetime, considering frequency of maintenance and replacement?

From this perspective, cast iron is one of the most cost effective pipe materials to choose.

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Did you know ?

Cast iron systems are manufactured from up to 95% recycled content (scrap), are 100% recyclable using harmless processes and do not lose any of their mechanical properties over time.