Ramesh R. Gopal *

Seen the ghastly seepage marks on the walls of homes of all categories of people? Noticed the mental, physical and monetary agonies of the occupants? Buildings and homes are built to last 60 years or more, but your plumbing is not. Well, this could be a thing of the past if stainless steel plumbing is used. This is because stainless steels are highly corrosion resistant. They are eminently passive (non-reactive) in the full range of potable water chemistries, environmentally friendly and ensure that the quality of water that enters your building is the same that comes out of your tap during the life of the building.

The As a result of the excellent corrosion resistance of stainless steels, there is no need for corrosion allowance and this allows thin-walled components to be used. These are lighter, simpler to fabricate and install compared to other materials; and also cost-effective. These properties, and the experience of over five decades in various water works of the world is making stainless steel the preferred material of construction for distribution lines, service lines, potable water treatment and sewage treatment plants.

In 1997 the Tamil Nadu Water Supply and Drainage Board (TWAD) took a bold decision and replaced their existing cast iron raw water rising main from the Mettur Dam reservoir with a stainless steel line. They were facing severe problems due to corrosion of the cast iron pipes - namely leakage and pressure drops and expensive repairs/replacements of sections every two or three years. The life of the cast iron line was a little over 20 years. Salem Steel Plant offered the stainless steel option, costing not much over the existing line. A conservative life assurance of 50 years was given, although it could probably go on for many more decades.

Although weight for weight, stainless steel costs about five times that of cast iron, Salem Steel Plant assured TWAD only a moderate increase in cost, near elimination of leakages and repeated expensive repairs, and a substantial reduction in the electrical energy costs for pumping the water up. The design details given below tell you why the installed cost of stainless steel option was to the satisfaction of TWAD officials.

Material	Cast Iron	Stainless Steel
Wall Thickness	13 mm	3 mm
Flow Coefficient	100	50
Service Life	20 yrs	50+ yrs

The wall thickness reduction is because of not having to give corrosion allowance (i.e., not having to add up extra wall thickness in the design to compensate for the anticipated thinning over the years due to erosion or corrosion) and the higher strength of stainless steel. Now, after seven years of service, there has been "zero maintenance" in the line and tremendous savings in electricity bills. TWAD is very happy about the bold step taken years ago (see accompanying photo).

Raw water supply line, Mettur, Salem, Tamil Nadu.

Tokyo plugs leaks with stainless steel service pipe

Tokyo was faced with about 15% water loss because of leaks in the system, including from underground service piping made of lead between the sub-main under the street and the water meter in the Buildings. They have replaced these with stainless steel grade 316 for all the dwellings and this has brought down the overall leakage in the system to 5%. The cost of the stainless steel system was reduced by introducing corrugated pipes, which not only reduced the number of fittings required, but also helped in accommodating the tremors in earthquake-prone Japan (see accompanying photo).