High and Dry: Climate Change, Water and the Economy (World Bank, 2016), projects that much more water will be needed in the next 30 years, 85% more in energy production, between 50 and 70% in municipal and industrial demand and 40 - 50% in the food sector. Some three billion people will face water scarcity by 2040.
By 2025, the world’s growing population will mean that demand for water will exceed supply by 40%. Nickel-containing materials can help provide water safely and efficiently while conserving existing resources.
The report highlights how improvements to water infrastructure can reduce the risk of scarcity. Current water losses around the world are unsustainable. In many developing countries, 50% is lost through leakage between the treatment plant and the consumer. Even in developed countries, losses above 20% are commonplace. By improving water infrastructure and by eliminating leaks, and doing so efficiently and sustainably, it is feasible to secure our water future.
Nickel-containing materials, such as stainless steels, lie at the heart of water purification, transport, collection and wastewater disposal. Comparing a water treatment plant (WTP) from half a century ago with its modern equivalent shows the advances that have been made. Rather than relying on coated carbon steel, cast iron, galvanised steel and similar materials for pipework and other components, these same items are now made using stainless steel.
The advantages of nickel-containing materials
Nickel-containing stainless steel offers low maintenance, simple fabrication and provides resistance to water and the chemicals used to make it safe. Stainless steel offers sound economic benefits that are not restricted to maintenance costs. Cement mortar-lined (CML) steel and ductile iron piping is limited to water velocities below three metres per second, as is copper. Stainless steel, however, can withstand water velocities of up to 40 metres per second. This vastly improves efficiency in both the treatment and delivery of water.
In a typical water treatment and delivery system, Type 304 (UNS S30400) will be used, Type 316 (UNS S31600) in higher chloride environments. These austenitic grades provide a proven track record of reliability and ease of fabrication. The duplex stainless grade 2205 (UNS S32205) can provide a tensile strength nearly twice that of carbon steel. Duplex stainless steels allow the water industry to use thinner sections, thus reducing both weight and cost and are increasingly popular.
Nickel-containing stainless steels are used throughout the water cycle, from water harvesting to wastewater disposal. They offer the ideal combination of high strength and low maintenance, with a lifespan greater than 100 years, more than compensating for any higher initial investment.
Many Asian countries have adopted stainless steel tubing to replace the lead, copper and plastics as a mains-to-meter service pipe solution, eliminating leaks in water distribution in the process. In many countries, nickel-containing stainless steel is also used in hot and cold plumbing applications. This provides a guarantee of durable, contamination-free drinking water.
The extreme conditions in reverse-osmosis (RO) seawater desalination offers a further illustration of the trend towards nickel-containing stainless steels in securing our water future. RO plants, whether operating or planned, would not be possible without super-austenitic or super-duplex stainless steels. These materials are used in key components such as pumps, pipework and valves. It is no surprise, therefore, that nickel-containing stainless steel has become the material of choice for durable materials solutions in the water industry worldwide.
Nickel-containing stainless steels find applications throughout the water cycle; in treatment, distribution, plumbing, wastewater and desalination.
Surface and groundwaters need to be treated to provide safe, quality drinking water.
Conventional materials, such as cast iron and CML steel have been superseded by stainless steel. Stainless steel offers hygienic surfaces for the treatment and delivery of drinking water combined with low maintenance without the need for coatings or linings. These and other benefits, such as high allowable water velocities, offer significant benefits for water utilities.
Types 304 and 316 (UNS S30400, S31600) predominate, but duplex stainless steels, are increasingly used.
Stainless steel can be used for distribution mains and has been successfully used for relining pipes made from other materials. Its ability to provide an excellent service life within older corroded mains makes it an increasingly attractive option.
However, stainless steel is providing improved options for mains-to-meter connections. In the water cycle, the majority of water loss in a distribution network happens in these service pipes. Alternative service line materials have led to extensive leakage, resulting in significant water loss, sometimes reaching over 50 percent.
In Tokyo, unsustainably-high leakage rates in the main-to-meter connections prompted the renewal of these components. All connections - around 2.2 million - were replaced with Type 316 stainless steel. The introduction of flexible, corrugated stainless steel allows the pipe to be bent easily without tools, and be installed in complex networks. Tokyo now has one of the lowest leakage rates in the world. Tokyo was so successful that a number of other Asian countries have and are adopting the technology combining the strength, corrosion resistance, durability and other benefits of stainless steel with the flexibility associated with other systems.
Stainless steel tubing provides the best solution for plumbing needs. The tube is generally available in Type 304, or more typically Type 316, combining high tensile strength and durability with a non-toxic surface free from contamination issues.
Joining stainless steel plumbing tubes has also become easier with the introduction of a simple ‘pressfit’ and other systems. Installations using these methods need only simple, portable equipment that produces instant and effective joints with no need for brazing or welding.
However, as is the case with all plumbing materials, stainless steel must be correctly installed and commissioned to obtain the best results. Where the simple installation steps are followed correctly, the life of the plumbing system is likely to meet or exceed a 100-year design life while providing a permanent solution to the health, environment and corrosion issues surrounding other materials.
Wastewater shares many of the needs of water treatment and distribution, as well as other specific, and often, critical issues. These arise from extreme corrosivity that is driven by hydrogen sulphide (H2S) production and its conversion to products like sulphuric acid. Traditional pipes struggle to handle the demands of these conditions. In addition, chloride infiltration into wastewater streams can further increase corrosive conditions.
Stainless steel, with adequate selection and fabrication practices, is capable of resisting these environments. Type 304 and 316 steels predominate, with duplex 2205 (UNS S 32205) increasingly useful.
Good fabrication practice and careful hydrotesting and commissioning are essential for stainless steel in wastewater as much as they are for drinking water environments. In particular, weld tint needs to be removed and only clean water used in hydrotesting and commissioning.
Stainless steels are rapidly becoming the default material for wastewater treatment plants. Examples of use include piping, penstocks and an increasing range of proprietary equipment such as drum screens.
The demand for water worldwide is accelerating development of very large-scale desalination plants using Reverse Osmosis (RO). These have a capacity of up to 500 million litres a day, which requires treating 1000 million litres of seawater.
The crucial stages of seawater desalination require high-pressure seawater pumps, complex pipework and water treatment before seawater can enter the very high pressure desalination RO units at the heart of the process.
Materials for the RO pumps, the delivery pipework and the brine returns would not be feasible without nickel-containing stainless steel. Typically, super-austenitic and super-duplex stainless steels (with pitting resistance equivalent number (PREN) values above 40) will be required for any seawater service. For permeate, Type 316 is sufficient.
Fabrication, post-fabrication treatment and the cleaning/hydrotesting regime is essential for ensuring that the stainless steel components perform to the required specifications. In fact, these elements are probably more important than the precise materials chosen.
The growing global demand for desalination plants will lead to an increasing requirement for nickel-containing stainless steels to meet this need.