By: Ivan Ruiz Stubelj, Emerson Automation Solutions
The safe and cost-effective transportation of gases and fluids – especially when infrastructure continues to grow – is vital to the Middle East midstream oil and gas sector. According to the 2017 Pipeline & Gas Journal ‘Worldwide Pipeline Construction Report,’ out of the approximately 133,000 kilometres of new pipelines already planned or under construction worldwide, 14,800 kilometres of those are in the Middle East. But pipelines such as these face significant challenges, chief among them – corrosion. In these instances, the deterioration of the metallic structure of a pipe due to an electrochemical reaction between the pipe material and the environment inside the pipe can be attributed to several reasons, including fluid corrosivity, water deposits and other pipeline impurities. Corrosion can be devastating, leading to leaks and environmental and safety repercussions, financial risk and reduced transportation capabilities. It can also be difficult to detect, especially when trying to distinguish between localised corrosion in small areas or zones on the metal surface, and generalised corrosion that’s uniformly distributed over a much larger area. Furthermore, components that generate localized corrosion and possible leaks, such as inorganic acids, salts, CO2 and H2S, are often difficult to track within pipelines.
So, how can corrosion be tracked and pre-empted?
Traditional methods include In-line Inspection (ILI) tools such as ultrasonic inspection and pigging, which play a key role in detecting stress cracking, and direct integrity assessment methods, both of which have been adopted in the Middle East. However, many of these techniques come with significant obstacles.
For example, ILI tools often require specially configured pipelines and specifications related to pressure, temperature, flow range, tool length and more. Direct assessments are also normally only suitable for short pipeline sub-segment coverage with a limited number of data points. Furthermore, in the Middle East, where there are thousands of new pipelines planned in vast and highly remote areas with limited communications and power, in addition to transportation and logistics difficulties, these issues are only magnified.
It’s against this backdrop that alternative forms of integrity assessment, including non-intrusive, online corrosion monitoring and the Field Signature Method (FSM), are beginning to emerge. The Field Signature Method (FSM) of corrosion monitoring is based on feeding an electric current through a monitored section of a pipe, pipeline or vessel where the applied current sets up an electric field.
The field is monitored via voltage drop values between a set of sensing pins installed on the external pipe wall. The initial measurement sequence measures the voltage drop between all pairs of sensing pins. This sequence is called the Field Signature. Follow-up measurements are then compared to the Field Signature, where general corrosion is seen as a uniform increase in voltage drops between all pin pairs, and localised corrosion as a local increase in the values. Corrosion is then measured between the sensing pins, meaning that the complete monitored area is covered, not only under each sensing pin.
The non-intrusive FSM method is ideally suited to detect all types of corrosion and, in particular, to distinguish between localised and generalised corrosion, reducing the need for pipeline inspection gauging (PIG) and other costlier inspection methods.
Typical detection sensitivity for generalised corrosion is 0.1 per cent of wall thickness for outer pipeline diameters between six and 48 inches. Utilising this technology, Emerson recently introduced the Roxar FSM Log 48 Area Corrosion Monitor, a pipeline integrity management system that provides continuous online corrosion and erosion monitoring in remote and large pipeline areas.
By being able to access real-time pipeline health information, operators can then make better decisions about when and where to conduct PIG runs, integrity digs and hydrostatic pressure tests. The Roxar FSM Log 48 - with 48 referring to the number of pins in the sensing pin matrix - has a total cost of ownership less than just one typical smart PIG run of up to 10 kilometres (although this can vary according to the PIG technology).
WLAN and cellular data transfer protocols as well built-in solar power options enable the solution to operate in remote areas. The systems are also specifically designed to work for both uncovered and buried pipelines and are easily installed on bottom pipe sections where water collection is most likely.
They can be retrofitted to existing uncovered or buried pipelines and several units can be located over a pipeline, minimising the need for PIGs to assess pipeline integrity and increase transportation capacity. As pipeline coverage continues to grow and margins continue to narrow, pre-empting the negative consequences of corrosion has never been more important. Through the emergence of new technologies such as FSM, our ability to implement accurate corrosion detection in remote and hard-to-reach places is fast becoming a reality.