Condition Assessment Outputs - What Do They Mean

Abstract

Condition assessment of pressure water and sewer mains has become increasingly important over the past 20 years. Nowadays, there are several service providers offering a range of technologies, with varying outputs. This paper discusses some of the outcomes derived from a range of technologies, including acoustic measurement techniques, soil testing, electromagnetic spot measurements and pressure monitoring. These are presented for grey cast iron, ductile iron, mild steel and asbestos cement pipelines. In general, quantitative outputs are preferable, and those which have a direct relationship with failure modes of the pipe material are far superior. The failure modes of each of the four materials above are briefly presented based on observations of failed pipe over the past 30 years. Grey cast iron and asbestos pipes are brittle materials that can fail without a deterioration in condition. Conversely, steel and ductile iron, which are stronger and tougher. Commonly Commented [MT1]: Does this sound better? derived and used outputs, including average wall thickness, average minimum wall thickness and minimum Grey cast iron and asbestos pipes are brittle materials that can fail without a deterioration in condition. Conversely, steel and remaining wall thickness are discussed in detail. The only one which is considered to provide a meaningful result is ductile iron, which are stronger and tougher… minimum remaining wall thickness. The primary reason for this is based on large variation of condition both within an individual pipe, and from pipe to pipe. As an example, for 350m length of grey cast iron in a very corrosive soil environment, less than 10% of individual pipes were found to be in Poor Condition. From consideration of even smaller lengths (say into 100mm sectors), the proportion of those sectors in Poor condition is much less than 10%.

Techniques