There are about 3.5 million kilometers of oil and gas pipelines worldwide needing regular cleaning, inspection and maintenance, according to the U.S. Energy Information Agency (EIA).
A pipeline’s insides are increasingly subject to inspection by smart pigging devices (known as inline inspection tools, intelligent or smart pigs) to detect corrosion, wax deposits, cracks and more. Smart or intelligent pigs are tools that run in the pipeline with integral sensors that detect, record and store details about the condition of the pipe for central analysis to guide maintenance and repair activities. Inline inspection (ILI) tools house a variety of technologies that have specific “missions” in detecting defects resulting from pipeline threats.
Today, North America accounts for around 48.5% of the global market, followed by Europe (19.4%) and Middle East & Africa (8.8%). World leaders in IL technology and services include companies such as T.D. Williamson, ROSEN Group, GE Oil & Gas (PII Pipeline Solutions), NDT Global and Enduro, among others.
Why Are Intelligent Pigs Used?
ILI tools inserted into the pipeline at special pig launch-and-receive facilities (commonly called traps) and typically move with the flow of oil or gas at speeds of between 0.5 and 3 meters per second (m/s).
ILI tools offer time savings, environmental and safety benefits. According to Mike Kirkwood, Market Development director – Transmission, at T.D. Williamson, “Using inline inspection tools provides the operator with the added advantage of not shutting down the pipeline to detect potential integrity threats. Alternative methods such as a hydrotest (where the pipeline is filled with water and subjected to a pressure higher than its operating pressure) can be costly and time-consuming.
LI tools are packed with sensors and electronics for measurement and data collection for monitoring the pipe’s condition. The sensors, electronics and power source (batteries) are protected from the extreme pressures and high temperatures of a pipe’s interior in what are basically pressure vessels. Data are recorded through the use of solid-state memory and then, once extracted from the pipeline, downloaded and analysed using expert data analysts.
ILI tools vary in terms of function. One important parameter is diameter. As the diameter of the pipe reduces, the amount of space available to accommodate inspection technologies also reduces, hence, the length increases. So, for small-diameter pipelines, the tools are long – about 2 to 4 meters, large-diameter tools can be short, say, 1 meter.
Likewise, the technology employed varies according to the required function. For example, levels are often detected using magnetic flux leakage (MFL) tools, whereas cracks require an ultrasonic technology (UT) or a derivative called electromagnetic acoustic transducers (EMAT). Simpler ILI tools can also be used to detect changes in internal geometry such as ovalities, dents and expanded pipe. A more recent trend is to combine technologies, enabling the detection and assessment of combined or interacting defects, such as dents and corrosion, cracks in wrinkles, etc.
As pipelines enter more challenging environment such as deepwater offshore and higher temperatures, and transport different and more aggressive products, new inspection technologies are being brought to the market. For example, Norwegian pipeline and subsea inspection business Halfwave AS offers pigs using acoustic resonance technology which has the ability to look at very thick-walled pipe that is not common onshore.
The frequency of inspections also varies. Recently built pipelines in the U.S. require inspections every five to seven years, depending on whether it is a gas or a liquid line. Others, such as the gas pipeline interconnectors that link the U.K. pipeline network with its neighbors in Belgium, Holland, Ireland and Norway, are inspected on average every two years, reports British energy regulator OFGEM. Regulations also play their part in setting the periods for re-inspection: rule-based set intervals following a given time period (e.g., five and seven years) vs. goal-based where the period is set on the basis of risk.
Drivers Behind More Inspection
Tightening regulations are a major factor in continued demand for ILI services. According to Kirkwood, “The world market for ILI services is about $1 billion a year and growing by around 6% a year, due to more stringent regulatory and changing supply/demand needs.” Economic recovery and increased consumption of petroleum products for vehicles and natural gas for electricity will also increase demand for ILI services as pipelines are maintained as major energy arteries.
ILI tools are not infallible and still experience limitations of detection when defects are small enough. In addition, if cleaning pigs are not used to clean the pipe before the smart pig is sent in, those “misses” can multiply with possible expensive consequences. Therefore, cleaning generally goes hand-in-hand with smart pigging programs.
There is also the consideration of cost. The United Kingdom Trenchless Society reports that the cost of carrying out an intelligent pig survey is expensive – about $607 per meter. While this may represent good value for maintaining the integrity of long-distance pipelines such as the Rockies Express 2,723-km natural gas pipeline, it is unlikely to be economically feasible for water mains.
During an ILI run, the tool is unable to directly communicate with the outside world due to several factors, including the distance the pipeline is underground or underwater and the materials that the pipe is made of. Plus the tool is at about 3 m/s. It is therefore necessary that the tool uses internal means to record its own movement during the trip.
This can be achieved by use of odometers and gyroscopes that measure tilt and XYZ location backed with geographical position. The tool records this positional data so that the distance, including that along the way, can be interpreted later to determine the exact path taken.
Another problem facing pipeline owners, and at the same time constraining the market, is that, according to Kirkwood, “Some 40% of transmission pipeline cannot be easily inspected by standard intelligent tools.” Since tool passage may be impeded by reductions in diameter, valves, pressures, temperature, etc., lines can be incompatible with standard inspection devices.
However, many of the ILI providers are looking at novel ways to enter these challenging pipelines; they are also non-intrusive methods such as direct assessment, which will mean most all pipelines can be brought up to acceptable integrity levels.
Current, Future Developments
Improved miniaturization and increases in computing speed and battery life have significantly reduced the cost of advanced ILI runs. Increasing diversity of function is also a trend.
“We are seeing the development and usage of sensor devices carrying out a whole range of duties and missions,” said Kirkwood. In this way, the next generation of tools will provide the best integrity picture in a single run.
Alongside this, we are seeing the ongoing development of tools to produce more accurate information on metal loss and crack detection, facilitating a significant improvement in inspection reports. Operators are customarily supplied with pipeline listings detailing every weld, fitting and feature, whether it be from corrosion or mill/manufacturing in origin.
As part of the service, the operators now receive software, which allows the pipeline’s engineers to view, and in some cases, manipulate the data from which the report is produced. Operators view the tool-recorded signals and can generate their own listings, filtering the report along criteria such as the percentage of metal loss, clock position and sentencing, thus significantly enhancing the inspection report. The quality of the report is one of the most critical parts of the inspection project. It is, after all, the end-product for which the client is paying.
Kirkwood believes “inspection is a primary element in the proof of an effective integrity management program, but it’s only a snapshot of the current status. In the future, additional data sources will be live, contributing to the current and future views of the pipeline’s health.” This will be the subject of future articles as technology becomes available to collect, manage and support decisions based on real-time data and predictive algorithms.