Pros and cons HDPE-Cast Iron Water supply
- long service life, especially HDPE 100
- corrosion resistant
- fewer welded joints which are a potential source of leaks
- relative flexibility, so less cutting in urban areas
- high sensitivity to certain chlorinated treatments
- sensitive to temperature variations, making connections to existing networks critical if these are fragile
- permeable to hydrocarbons (problem can be solved with suitable HDPE and KIWA liners)
- limited leak detection because the material does not propagate sound well; the only solution is to install hydrophones
- risk of out-of-roundness if the backfill around the pipe is poorly compacted
- undetectable with conventional geo-detection tools (disadvantage can be overcome by adding utility markers)
- high mechanical strength
- proven material
- good sound transmission for leak detection
- fairly good detection with conventional geo-detection tools even if the signal decreases at each joint
- sensitive to corrosion
- sensitive to shocks during installation
- weight quickly increases with increase in diameter
- installation of joints every 19.5 feet, multiplying potential source of leaks
I would also say that not all cast iron and HDPE is created equal. For cast iron, an outer anti-corrosion layer is essential. Some manufacturers use a zinc/aluminum alloy on the pipe while others use zinc and aluminum but not an alloy, which is a game changer. The alloy is preferable.
As for the HDPE it should be rated 100; this guarantees the use of virgin resins, which in turn ensures longevity.
The price difference between the two materials becomes almost zero the closer you get to DN 150, below which HDPE is cheaper.
Beyond the question of materials, the most critical point concerns the installation. It is important to ensure that it is carried out according to accepted standards.
For PE, in particular, welded joints require special installation conditions that are not always respected in the field (cooling time, exposure of the pipes to the sun before installation, scraping of the pipes not performed before insertion into the sleeve etc.).
For cast iron, watch out for roughly joined spigots and sockets, overly tightened flanges, inadequate locking, careless handling of pipes, etc., which can later give rise to defects that won’t necessarily be visible during pressure tests but will result in premature leaks.
The working habits and experience with the material on the part of the different installers is a key factor in ensuring the best possible lifespan for any infrastructure.
A good pipe laid under poor conditions by people who don’t abide by professional standards will result in poor performance. When considering the costs, be sure to take these points into account.