Guided wave pipeline inspection. Source: Sprialboy Guided wave pipeline inspection. Source: SprialboySeveral conventional corrosion sensors have been used to monitor oil and gas infrastructure. The added value they provide in identifying deterioration comes in the form of salvaged resources, scheduled maintenance and mitigated downtime. To further increase value, operators need precise early corrosion onset detection. Continuous, real-time monitoring sensors that achieve this feat allow operators to capitalize on the investment.

The Pipeline and Hazardous Materials Safety Administration (PHMSA) estimates that 25% of the natural gas transmission and gathering pipeline incidents over the past 30 years were attributed to corrosion, predominantly internal corrosion. The National Energy Technology Laboratory (NETL) found that conventional technologies used to identify corrosion including corrosion coupons, electrical resistance probes, electrochemical sensors and indirect sensing methods were ineffective in providing continuous, real-time early corrosion onset detection across extended lengths of oil and gas infrastructure.

Corrosion coupons are a point location corrosion sensing technique and only identifies an average corrosion rate. Electrical resistance probes provide the added value of real-time connectivity, but still fail to identify anything more than uniform corrosion at point locations. Electrochemical sensors provide both connectivity and sensing range, but the excitation source poses an increased oxidation potential and they only work with conductive aqueous solutions.

Conventional sensing technologies also include several indirect conventional corrosion sensing techniques. These sensing techniques are inclusive of ultrasonic sensors that measure wall thickness, magnetic flux leakage methods, electromagnetic based sensing methods and pipeline inspection gauges. NETL found that these technologies also failed to provide continuous real-time monitoring of oil and gas infrastructure or were otherwise unable to precisely detect early corrosion onset.

NETL suggests that new emerging technologies were the most effective method of monitoring oil and gas infrastructure and identifying early corrosion onset before structural integrity became compromised. These technologies inclusive of optical fiber sensors (OFS) and passive wireless sensors pose several advantages.

A matrix of OFS can be installed to provide for either point, quasi-distributed, or distributed in-situ monitoring applications. They are small, lightweight, demonstrate inherent immunity to EMI and provide long reach. Distributed OFS was found to be particularly well suited for monitoring long-distance infrastructure, such as transmission pipelines. They provide both high spatial resolution and early corrosion onset detection.

Passive wireless sensors are small, cost-efficient, adaptable and compatible with wireless telemetry. No excitation is required. They are also durable and provide for enhanced stability in harsh environments and in high-temperature high-pressure wells. Their use has been explored for corrosion monitoring, structural health monitoring and for monitoring of physical parameters such as temperature, pressure and strain. Due to their small size and low costs they can be installed at the user’s discretion.

NETL found OFS and passive wireless sensors are two emerging technologies that show promise for improving the accuracy and the spatial resolution of corrosion and structural health monitoring of oil and gas infrastructure. They support continuous, real-time sensing functionality with high sensitivity and stability and collectively address numerous applications.