Although stainless steel is not a standard material for distribution systems handling clean treated waters, it has and can act as a materials solution to several problem areas where ease of transport, high corrosion resistance, strength and toughness through all temperature ranges are required. In the USA, an organization SPLASH, Stop Leaks Ask for Stainless Steel Help, was set up in 2004 involving an alliance of the Nickel Institute, the International Molybdenum Association, stainless steel producers and water distribution equipment manufacturers and suppliers. Information about projects and applications which have resulted are discussed on their web site; www.s-p-l-a-s-h.com
In Japan, an example of where light-weight designs have been advantageous for water distribution systems are the use of stainless steels piping attached to river bridge crossings. In Tokyo, carbon steel bridges carrying drinking water had to be painted every 5-7 years. Analysis showed that whilst the installed cost of a stainless steel water bridge would be 10% more expensive, the saving in maintenance costs would result in an overall cost saving of 40% over 30 years. Newly installed water bridges in Tokyo are in stainless steel type 316 (e.g. 1.4404) piping. At coastal sites where the environment is more severe, 25% Cr duplex has been used for the span and 22% Cr duplex for the risers into the soil at either end.
In Tokyo too, the leakage rate in the early 1980’s was 40 – 45% of supply. To build a new reservoir to meet the growing needs was basically impractical, especially in the country with limited land availability. As of 2000, all of Tokyo’s 46,000 service connectors had been replaced with type 316 stainless steel with excellent results. The connectors were insulated both from the ductile cast iron submain in the steets and the meter at the dwelling to prevent galvanic corrosion. The bends in the service water piping provide flexibility to resist road traffic, ground subsidence and earthquake damage.
In the Italian cities of Turin and Padua, disruptions to traffic have been avoided by using trenchless technology. Piping in Type 304 stainless steel has been inserted down the old asbestos cement and cast pipes using a special hydraulic ram. The longest assembled liner was 1000m and pipe diameters were 550mm in Turin. Tube sections 1,500mm long weighing 50 kgs were welded on and inspected in small sunken chambers 2.5m x 2m and before being pushed down the existing main. In Padua, 6m lengths were used and assembled in an open pit. Stainless steel was chosen as the preferred liner after a 15 year material test programme.
Repair clamps, couplings, welding saddles and tapping sleeves in stainless steel are common place internationally. The repair devices are designed to be slipped over leaking sections of main and bolted tight. The elastomeric liner provides a seal to stop leakage. The thick liner also insulates the stainless steel body from cast iron or ductile iron piping. These type of devices have a 25 year plus track record of good performance in the same variety of soil conditions as the water mains themselves.
Articles & Publications
Stainless Steel Valves
New York City's recent endeavour, a US$6-billion mega -project known as Water Tunnel No. 3, began in 1970 and is due for completion in 2020. It is a huge user of nickel-containing stainless steel. (Nickel Magazine, Mar. 2004)
Piping for Municipalities
Stainless steel pipe to be buried in a municipal water distribution project in Green Bay, Wisconsin, U.S.A. (Nickel Magazine, July 2005)
Municipal Water Tank
Why a city in the U.S.A. chose stainless steel to build a water tank that stores rain water. (Nickel Magazine, Nov. 2005)
Why Replace Existing Piping?
The University of Missouri-Columbia is replacing carbon steel water distribution piping with austenitic stainless steel to reduce maintenance costs. (Nickel Magazine, Mar. 2005)
A Precedent-Setting Pipeline
Nickel-containing stainless steel has been used for the first time to construct a buried water pipeline in North America. (Nickel Magazine, Oct. 2003)
Water Tank Built to last 60 Years, NI Publication 14030
Corrosion Resistance of Stainless Steels in Soils and in Concrete (EuroInox) www.euro-inox.org