ABSTRACT

PipeMonit* and UltraMonit are well established corrosion monitoring tools based on ultrasound, and can be used for monitoring pipelines both subsea and topside/onshore. The tools are non-invasive and provides real-time and online wall thickness data on subsea spools, elbows, pipelines and pipes. The ultrasound transducers measure wall thickness as a function of time and provide high resolution data on material wall loss. The sensors are installed directly on the pipe outer wall, or on top of the weld seam. This way the tools can monitor preferential corrosion and corrosion in Heat Affected Zones (HAZ). Preferential weld corrosion has high attention as this can be a serious issue for oil and gas industry. Sensorlink has developed a tool for monitoring the preferential weld corrosion by using the ultrasonic technique. A matrix of ultrasound transducers is mounted on the outside of the pipe where the center of the transducer is located at the center of the weld. This way one can follow the wall thickness trends on both the weld and the HAZ zone with high resolution.

In this paper field data from preferential weld corrosion monitoring is presented, and compared with other techniques used for monitoring.

INTRODUCTION

Corrosion monitoring of pipelines is an important aspect of integrity management, and techniques and practices have been systemized through standards. 1 Permanently installed equipment has increased in use over the past few years.2 Ultrasound techniques have been developed to complement traditional inspection with monitoring, to improve efficiency, data precision and data richness. As these permanently installed ultrasound sensors can be retrofitted without interfering with production, there is a low threshold for using this type of equipment. In addition, retrofitted ultrasound sensors can be a good compliment to corrosion coupons and corrosion probes, particularly as these intrusive techniques pose a risk to Health, Safety and Environment involving increased work and planning. One of the benefits from non-invasive techniques compared to invasive techniques is that they measure the actual direct wall loss of the pipe, instead of an indirect indication. Some of the non-invasive techniques are also easy to relocate if a change in monitoring strategy is required, and this flexibility allows the integrity engineer to optimize the monitoring strategy as the asset change or age. There are several publications discussing how corrosion monitoring should be performed in the most efficient way. 3 4 This is especially relevant now that we are facing a decrease in oil prices and an increased focus on profit. 5

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