Portable Data Logger for Pipeline Corrosion and Integrity Analysis based on NACE Standard SP0207-2007
"Using National Instruments technology, a reliable solution was
developed that is having positive results, has reduced testing costs, and
has improved the accuracy with which users detect anomalies."
- Erwin Franz Rodriguez, Erlab SA de CV
The Challenge:
Build a rugged and portable device capable of performing NACE´s recommended indirect corrosion surveys. The equipment
should be synchronized with a cathodic protection system through a GPS antenna. It should perform high-speed analog
measurements and log the synchronized data.
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The Solution:
ISMARTLOGGER, a portable and easy-to-operate data logger based on the LabVIEW RIO Architecture, designed for corrosion
engineers and technicians, to perform CIPS and DCVG testing correctly, including the combined technique for CIPS and DCVG.
Author(s):
Erwin Franz Rodriguez - Erlab SA de CV
Introduction:
Corrosion is a leading cause of pipeline failures. In 2002, the National Association of Corrosion Engineers (NACE) published the International Recommended Practice RP0502-2002.
This document established that pipeline operators are required to utilize a minimum of two indirect method tools (CIPS, DCVG) to assess the effectiveness of corrosion control
method(s) on underground and underwater pipelines. Nowadays, there are very few equipment options on the market to perform these surveys. Most survey equipment was
designed approximately 10 years ago and is unable to perform online analysis, nor does it have a floating-point processor. Being unable to perform these calculations impacts cost
because each operator is obligated to complete at least two surveys per right-of-way in order to validate the initial results.
Application description.
According to figures from the European Gas Pipeline Incident Data Group (EGIG) and Pipeline Research Council International (PRCI) Department of Transportation (DOT) (USA), in
the last 30 years, corrosion has caused, indirectly and directly, more than 30% of incidents or failures in the distribution of hydrocarbon products by pipeline.
Currently, impressed-current cathodic protection is one of the most effective techniques in preventing corrosion. In the oil and gas industry, it is repeatedly used to prevent pipeline
infrastructure from corroding during hydrocarbon distribution. With this technique, a current rectifier is connected from its negative terminal to a pipeline and from its positive terminal
to an anode bed.
Upon starting the system, the corrosion process only occurs on the anode side while preventing galvanic corrosion in the cathode side or pipeline. Designing cathodic protection
systems involves determining several variables, including the number of anodes, anode type, the distance between the anode and the pipeline, and the current/voltage capacity of
the rectifier to ensure protection of the entire pipeline area, etc.
The current injected into the pipeline induces electrical potential that can be measured with copper sulfate surface electrodes and a data acquisition system with signal conditioning to
filter noise and read signals in the mV order.
Pipeline Integrity Studies for Systems where Cathodic Protection is Used
The Close Interval Potential Surveys (CIPS) technique is used to generate a detailed profile of the differences between electrical potential in pipelines and on the ground. The profile
is primarily used to determine the quality or status of cathodic protection. This technique requires a person to walk along the right of way to measure meter by meter the electrical
potentials that form the system profile.
To conduct a CIPS study, it is necessary to place a current interrupter between the rectifier and the pipeline. Electrical potential measurement is accomplished by connecting the pipe
to the negative terminal, and putting an electrode in contact with the surface of the right of way in the positive terminal of an analog measuring system. Regularly, the current
interruption is 200 milliseconds per second and should be done whenever receiving the signal pulse per second from a GPS antenna.
The current interrupter ensures that the data acquisition system measures the electrical potential at the surface receiving two different potentials: the activation potential (on,
representing the pipeline potential induced by the current and ambient noise) and deactivation potential (off, which only represents the electrical potential of ambient noise). The
difference in potential allows the corrosion technician or engineer to know precisely the potential free of the noise being induced on the surface through the work of the cathodic
protection system.
The Direct Current Voltage Gradient (DCVG) is a technique similar to CIPS but with the objective of detecting failures/defects/errors in the mechanical coating of pipelines. The main
difference between the two is the connection used for measurements. DCVG uses an analog differential measurement between two electrodes in contact with the surface or ground
area with at least one meter of distance between the electrodes. The test is based in part on the principle that in a pipeline with impressed currents, any defects in the coating will
cause electrical flow from the ground to the pipeline. This electrical flow has to be measured using a high resolution voltmeter that is fast enough to represent values by the second of
its different states (on and off).
System Development and Specific Functionality
In short, this development presented a big challenge, due to the multitude of requirements necessary to achieve the functionality described in NACE standard SP0207-2007. It was
necessary to build a system capable of synchronizing its measurements via GPS, continuously read its coordinates, include an odometer to guide the user, perform high-resolution
measurements in high-impedance sensors, have signal conditioning capable of filtering electromagnetic noise, calculate and graph the % of failure/error/defects (IR) using floating
point operations formulas, and to save, second by second, all the information generated by a report located within the same system.
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Synchronization with the GPS is an indispensable factor. Therefore, all equipment not running real time operating systems could not be considered. To ensure the parallelism of all
operations required to execute the studies, we decided to use the NI LabVIEW RIO Architecture, including hardware with a real-time processor, an FPGA and reconfigurable IO and
LabVIEW Real Time, and LabVIEW FPGA software.
The LabVIEW RIO Architecture allowed us to achieve mathematical calculations and conditioning filters at the real-time level using software, thus avoiding the need to implement
these circuits physically. No problems were encountered in realizing failure analysis or % IR drop in-line. The ISMARTLOGGER was able to generate files in .tdms format to register
each channel at the needed speed.
Using the NI platform-based approach allowed us to create lightweight and portable equipment, which we connected to a military-grade tablet via USB or WI-FI to visualize, at
runtime, calculations and graphs derived from the studies.
Finally, the different analog channels and sampling speeds present in the device allowed us to connect and measure signals properly, following the specific CIPS and DCVG
requirements.
Conclusion:
Currently, the cost and time required to complete CIPS and DCVG pipeline integrity studies are high and negatively affect efficiency measures in companies responsible for the
distribution of hydrocarbons. Many of these costs are related to expenses incurred to offset the lack of functionality of existing equipment. Failing to do floating-point operations and
mathematical calculations during right of way testing results in traversing right of ways numerous times to validate flaws that need to be repaired. Using National Instruments
technology, a reliable solution was developed that is having positive results, has reduced testing costs, and has improved the accuracy with which users detect anomalies.
Author Information:
Erwin Franz Rodriguez
Erlab SA de CV
Mexico
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