A material doesn’t get to last over a century in Australian water infrastructure by chance; mild steel pipe has outlasted a heap of changes in the industry. Its engineering properties have allowed it to continue being used despite regulatory changes and the emergence of new tech, as well as shifting best practices in construction. Understanding just why it performs so well, however, means you have to look beyond the pipe itself.
What Mild Steel Actually Is in the Pipeline?
Mild steel is a type of low-carbon steel that strikes a balance between having some real strength and being able to be welded and shaped fairly easily, although low carbon content is what makes it weldable; it also means it needs extra help to survive in water service. Left on its own, bare mild steel pipe will corrode away pretty quickly both in soil and water environments. For more information on mild steel pipe and its applications, visit https://www.steelmains.com/mild_steel_pipe.
In Australia though, it’s been consistently shown that using mild steel pipe correctly coated and lined means it can last anywhere between 50 to 100 years, not bad for a material that has a higher upfront cost compared to some of the other options out there. But the key word there is “correctly”. The pipe wall has the structural bits right, but the protection systems are the ones that make it last that long.
Why a Single Competitor Can’t Match What Mild Steel Can Do?
Mild steel pipe can be made in a pretty wide range of diameters, anywhere from the small pipe used for distribution up to the really big pipe used for the transmission mains, which can be bigger than 2000mm in some cases. We can either use a spiral weld or longitudinal weld process depending on the size and what kind of thickness is required. Pressure class is set depending on the wall thickness and the diameter of the pipe and the operating pressure, all of which we can work out using well-established design formulae. But what really matters here is that the same family of materials can cover everything from low-pressure gravity mains to high-pressure pumped transmission systems without having to switch to a different material or a different supply chain.
There just isn’t another pipe material out there that can match mild steel in terms of structural consistency across this range of diameters and pressures. That’s why you see it getting used so much of the time in major water infrastructure projects across Australia, particularly the ones where the project scope spans multiple pressure zones.
The Protection System on the Pipe Isn’t an Afterthought
For mild steel pipe in water service, the protection system is the make or break of whether it reaches its design life or not. External polyethylene coating protects against corrosion and gets knocked about during installation. Its performance has got to depend on how well it sticks to the pipe, how thick it’s applied, and if there’s any pinholes in the film. Then there’s the internal cement mortar lining that protects against corrosion and maintains the pipe’s hydraulic efficiency.
You can bet that the integrity of both systems at the joint zones is just as important as how well the manufacturer applies the coating on the pipe barrel. Joint zones are the bit where field conditions come in and can affect the protection continuity, which is why you need to have specific repair and inspection procedures planned out, as part of the installation spec, long before the project ever starts.
Wastewater Applications Have an Altered Specification Requirement
The mild steel piping that serves in wastewater applications requires more advanced corrosion protection mechanisms compared to those in clean water applications. Hydrogen sulfide formation in wastewater systems will attack the cement mortar lining in the gas phase above the flow line. In high sulfide environments, standard specifications of the cement lining will not meet the required design lifetime, and that has to be established before the procurement process as opposed to learning about it after asset inspection.
In situations where the presence of hydrogen sulfide is known through testing and analysis, then the lining system recommended will be epoxy or polymers together with the mild steel pipe walls. The base metal remains the same while the corrosion protection mechanism differs based on the actual environment.
Timing for Procurement Is a Project Risk
The procurement of mild steel pipe in major water infrastructure projects is usually a long-term procurement process. The manufacturing, coating, and lining of large diameter pipe normally takes months, and late design changes will make recovery from them very difficult and costly. Pre-construction design assistance from pipe manufacturers in major water infrastructure projects in Australia is a standard procedure, and this has been seen to consistently improve project cost and program results.
