1. INTRODUCTION

Ductile iron is one of the most commonly used pipe materials in our modern society. The first ductile iron pipe was cast experimentally in 1948 and was introduced into the marketplace in 1955. By the late 1970's, ductile iron pipe had replaced gray cast iron pipe in the marketplace. Cast iron is an old principal pipe material that was used particularly for water and wastewater service in North America for the past 150 years. Today, ductile iron pipe is widely used in the transportation of raw and potable water, sewage, digester gas, slurries, and process chemicals.

Deterioration of underground pipes due to corrosion or mechanical failure is of increasing concern to users in both the private and the public sectors in North America and other countries.  The primary concern relates to the increasingly large number of leaks that have occurred in potable water and sewage systems. The demand for privatization within the water industry to yield cost savings, as well as more aggressive pressures from governments to reduce wastage of resources, has meant that methods of preventing the rate of deterioration of buried pipes has become an important issue.

As the number of ductile and gray cast iron buried piping systems far exceeds the number of other types of water distribution systems, it would be expected that corrosion of both ductile and gray cast iron would have received major attention from engineers, municipals, water companies,

and pipe producers.  It is interesting to note, therefore, that a notable lack of consistent opinion appears   to   exist  on  issues  such  as  failure  mechanisms,  corrosion  resistance, and  optimal

corrosion control methodologies for buried ductile and gray cast iron pipelines. Such controversies can be for example seen from the 1992 NACE International Report from its Task Group T-10A-21 on Corrosion Control of Ductile and Cast Iron Pipe

The present paper focuses on corrosion and protection of buried ductile iron pipe. External corrosion mechanisms and corrosion resistance of ductile iron pipe are reviewed. In addition to considering the relative merits of uncoated cast and ductile iron pipes, the value of corrosion control measures such as bituminous coatings, sacrificial metals, polyethylene encasement, tape wrapping, bonded coatings, cathodic protection, the impact on cathodic protection of electrical insulation at pipe joints, and the value of improvements in trenching methods are evaluated.