Oil & Gas
Identify the key risks and keep them under control
A long and healthy life
Offshore oil and gas production assets are continuously subjected to extreme forces through wind, waves and salty water. Also the products themselves are often not the most benign. Corrosion and fatigue can thus have a significant influence on the structural integrity of the assets used. Both safety as well as preventing environmental damage are essential focus points of every operator active in the industry. Moreover a continuous follow-up of all phenomena that could have a negative impact on these aspects comes with a significant value. Because it will result in early detection of issues and therefore timely and well-prepared repairs such as:
Cathodic Protection (CP) performance
Fatigue of jacket structures (nodes)
Zensor offers you integrated monitoring solutions that are the perfect tool for the long-term remote follow-up of these phenomena.
Buried pipelines are used in various applications. They play a key role in the safe transport of oil and gas, water and refined products over long distances.
To protect these pipelines from external corrosion a 2-way defense mechanism is implemented:
At first the pipe is coated with a thick organic coating, preventing contact between the pipe metal and the potentially aggressive surrounding soil.
Additionally a cathodic protection (CP) system is put into place. Most frequently an impressed current (ICCP) system is used here. An electrode of an inert metal is buried in a location near the pipe. In operation a current is imposed between the pipe and this additional metal electrode to render the steel to be protected the cathode in the electrochemical system. Once the potential of the steel is below a certain value, the metal is thermodynamically protected against corrosion attack.
This combination often succeeds in guaranteeing a long service life for the buried pipe, but in practice pipelines are still damaged by corrosion attack at multiple locations during their operational life.
Making the impossible possible
A multitude of techniques is available to investigate the circumstances potentially leading to corrosion damage. Coating defects can be located using aboveground techniques such as DCVG (Direct Current Voltage Gradient), Pearson tests or others. In complement one can conduct a Close Interval Potential Survey (CIPS) to record the pipe’s potential along its trajectory or employ other techniques to assess the state of the CP system connected to the pipe. As such it is possible to single out locations where corrosion is potentially occurring, based on thermodynamic data.
It is however still impossible to assess in a simple way whether or not active corrosion is taking place at these locations. Dig up and visual inspection of the surface remains to be the preferred operation, but this is a very expensive and involved procedure. In practice 1 out of 2 digs reveal that no active corrosion is taking place at the pipe metal. As a result, there is need for a tool to prioritize dig locations and timing to allow an optimized planning of these operations.
In this respect MobiZEN presents itself as the right tool for the job. It is a device (patent applied) recently developed at the SURF Research Group within the Vrije Universiteit Brussel, Belgium. Using this instrument it is possible to determine whether or not active corrosion is taking place at the surface of a buried pipeline.
How it works
The MobiZEN device is placed near the defect site. A connection is made between the pipe metal (using for example the connection points for coating inspection) and the sensor device. Subsequently a number of sensor electrodes are pressed into the soil at a distance from the pipeline, distributed along the defect site.
All of these electrodes are in turn also connected to an input channel of the sensor device. Subsequently MobiZEN is launched. The device applies a tailored, multi-frequency, low-amplitude AC signal between the pipe and one of the auxiliary electrodes. The response of the system is recorded. An algorithm processes the data and calculates an equivalent corrosion rate.
Measuring corrosion rate
This corrosion rate value is stored and the measurement is repeated multiple times and using multiple of the auxiliary electrodes. Plots are generated presenting the evolution of the corrosion rate for each electrode over a period of 24 hours. Knowing the lateral distance between the electrodes a spatial distribution of corrosion rates is given as well, giving an idea about the size of the corroding area.