Recent Advances in Pipe Wall Assessment Technology

Abstract

Most of North America's oldest water mains are constructed of ferrous material, in particular cast iron, ductile iron, and steel. As utilities rarely have funds to replace all of these pipelines at the end of their design life, utilities are forced to carefully target their replacement and rehabilitation budgets. Critical for this targeting of funds is the availability of accurate knowledge of the actual pipeline conditions, in particular assessing the condition of the pipe wall and its impact on the remaining useful life of the pipeline. With this clear and impending need, a variety of technologies are becoming available for pipe wall assessment. This paper details developments and advances over the past two years in several technologies for pipe wall assessment. The results provided by each technology are outlined, as well as how these results can be used to assess progression along the failure paths of various types of pipelines. The tools are grouped in a systematic way, illustrating how they fit into three fundamental philosophies towards condition assessment. Examples of their application are provided for tools advanced beyond the R&D phase. Abstract ID 112 1. FAILURE MODES OF METALLIC MAINS Pipes fail when some portion of the pipe is no longer strong enough to withstand the stress applied to it. This can happen when unexpected stress is placed on the pipe, or when the pipe loses enough strength to be overcome by the planned stress of normal operation. In most cases, it is a combination of the two: an unexpected stress, such as a water hammer, causes a failure at a point that has been weakened by one or more factors, such as cracking or corrosion. (Makar et al, 2001) Different types of pipe have various mechanisms of failure, and hence different failure rates. Cast iron pipes are by far the most prone to failure. Cast iron pipes corrode, are brittle, are prone to cracking, and generally employ bell and spigot joints that can lose their sealing integrity. Many older North American cities contain cast iron pipe installed in the 1800's, when methods of construction were not uniform and formal quality control (inspection) and pipeline standards did not exist. For example,