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This paper is a revised repeat of SPE 96568, presented at Offshore Europe in Aberdeen, Scotland, 6-9 September, 2005.

Abstract
Corrosion and erosion detection and monitoring are essential prognostic means of preserving material integrity and reducing the life-cycle cost of industrial infrastructure, ships, aircraft, ground vehicles, pipelines, oil installations, etc. Spatially dynamic pipeline monitoring systems have to necessarily face extremely hostile conditions of operation including surface roughness, fluid loading issues, temperature variations, and a host of other factors that make development of a robust wall thickness assessment tool a challenging task. This paper describes the working of Corrosion-Erosion Monitor (CEM) - an online, real-time path based thickness assessment tool that deploys a set of transducers over a given pipe area, and utilizes a dispersion based principle to assess wall thickness loss. This instrument was developed keeping the needs of the oil, gas and petrochemical industry in mind, both upstream and downstream, but because it essentially monitors reductions in wall loss, it can find applications in many other industries. Experimental work and field trials provide very promising results pertaining to the functionality of the CEM system, and some of these results have been discussed in this paper. The CEM can be used as a permanent installation or as a relocatable instrument, a result of the development of so called “dry contact” transducers. It is installed on the outer pipe wall to produce real-time pipe wall thickness information, not as a spot measurement, but as a unique average path wall thickness.

Introduction
The oil and gas industry faces large losses and setbacks each year dealing with the effects and consequences of corrosion and erosion on their structures, mainly pipelines. On many occasions, the generic area of commonly occurring corrosion and erosion is known, both from experience and from use of CFD analysis techniques. A lot of time and money is expended on inspecting these areas for loss of wall thickness by relying on a scheduled NDE program, typically employing a spot-measurement based thickness assessment, performed in a rather manually intensive manner. The CEM was designed to add value to the NDE inspection cycle of these industries by providing the inspector with advanced knowledge about the extent and severity of any corrosion or erosion based damage in the structure. With this information added to the database, the inspector can then schedule regular checks based upon the perceived severity of the damage. The transducers of the CEM are fixed at pre-determined spots on the pipe, and cover a fixed area of the pipe surface. The absence of any transducer movement or mechanical motion adds a high degree of robustness to the instrument, eliminating costly mechanical maintenance and possible failure. The CEM uses ultrasonic guided waves, called Lamb waves, to perform its measurement, covering a much larger distance along the pipe surface than any other spot measurement system with a comparable number of transducers.

The primary manifestation of any corrosion or erosion process is to reduce the effective thickness of the metal subjected to it. The CEM has thus been designed to assess the average wall thickness between any given pair of transducers, and will thus indicate the presence of possible material loss phenomenon underway in the pipe. The system is designed to use between two and eight transducers (depending on the pipe parameters such as thickness and diameter, and proposed coverage area). The inherent long term nature of corrosive phenomena renders the few minutes the system takes to perform its measurement a near real-time process.