Veins of Vitality How Inline Inspection (ILI) Sustains Pipeline Integrity Keeping it Safe

Table of Content

• The Ageing Pipeline Challenge
• The Role of Inline Inspection (ILI)
• Key Threats Identified by ILI Tools
• Sensor Development in ILI Technology
• The Importance of Validating ILI Technologies
• Plotting Dig Verification Feedback
• Looking Ahead: The Future of ILI

The world is crisscrossed with a nearly invisible pipeline network that truly supports everything that we as humans do, whether it’s providing raw materials for manufacturing or a fuel source to heat or cool homes, hospitals, schools, shops, or thousands of other uses. To say that the network is critical is an understatement.

The Ageing Pipeline Challenge

However, that network is ageing, and due to regulatory limitations and increasing cost of materials and construction services, the network is growing at a significantly reduced rate compared to prior years. As a result, the existing pipeline infrastructure is being repurposed continually, leading to an extension of the original design life of the assets. It’s fair to say that the original designs of older pipelines may not have contemplated advances in chemical treatments of corrosion inhibitors or cathodic protection, nor understood the real protection that some early coatings have truly provided.

With newer pipelines, improvements have been seen in manufacturing quality, resistant coatings, chemical treatments of the products they transfer, and cathodic protection, along with a whole industry full of smart engineers and scientists creating more and more life-extending solutions, such as the team at Onstream Pipeline Inspection, member of MISTRAS Group.

Now, the industry is challenged with ensuring that these valuable pipeline assets are fit for service and present minimal risk to those around them or the environment, while further stretching the lifetime of each pipeline.

The Role of Inline Inspection (ILI)

Pipelines can extend for hundreds of miles and are generally buried beneath several feet of earth, concrete, or underwater. Understanding the condition or health of the pipeline requires an approach that incorporates numerous data points surrounding the pipeline including the coating type, soil type(s), product flow/pressures, pipe materials, temperatures, product type, and multiple others.

Key data points are available to integrity engineers through the use of Inline Inspection (ILI) tools or “smart pigs”. These ILI tools are sophisticated electronic devices that use a variety of NDT and geospatial technologies to provide data on the condition of the pipeline from start to finish, rather than spot checks along the route. While they are incredibly useful in providing relevant information as a stand-alone tool, they are complementary to other data points that are considered in Pipeline Integrity Management.

ILI has been around the pipeline industry for five decades, and like everything around us, has developed to incorporate advancing technologies to meet new challenges. Early ILI tools were designed to identify corrosion at the 6 o’clock position of the pipeline, typically the most likely area where corrosion would be present. Current technology provides detailed data collected around the entire pipeline circumference, identifying both internal and external features as well as mid-wall anomalies, all while travelling through an operational pipeline at the speed of a recreational jog.

Modern ILI tools are designed to identify a wide range of pipeline anomalies and features and selecting the correct tool for the perceived integrity threat is part of common industry practice and regulation depending on the location. While corrosion or “metal loss” is likely the most common integrity threat, it’s not the most likely cause of loss of containment, which is third-party damage. Selecting the correct ILI tool to support an integrity program is based on the identified threats to that pipeline but of course, additional factors need to be considered.

Key Threats Identified by ILI Tools

What threats can currently be identified by ILI tools? The list expands as the industry drives forward but a summarized list is below. Not all ILI technologies can be utilized in every pipeline so in some cases, additional NDT Techniques may need to be incorporated at the dig level to provide more asset information.

• Metal Loss – Magnetic Flux Leakage or Ultrasonic Wall Measurement
• Internal Diameter – Caliper
• Crack Detection – Ultrasonic Crack Detection (angled or phased array)
• Electromagnetic Acoustic Transducer (EMAT)
• Hard Spots – MFL high/low field inspection
• Pipeline Properties – MFL, Caliper with complimentary in-the-ditch dig verification on select samples

Sensor Development in ILI Technology

The accuracy of the technology continues to improve with advancements in both hardware and software. MFL technology in particular has seen significant advances in sensor development with the inclusion of additional sensor vectors, like those in Onstream’s TriStream MFL™ tool, that were not available in previous tool generations.

MFL tools use strong magnets to magnetically saturate the pipe wall as the tool runs through the pipeline, using wear-resistant plates or brushes to protect the magnets from impact with girth welds, fittings, and wall thickness changes. The majority of MFL tools utilize Hall Effect sensors mounted between the poles of the magnets to measure and convert the magnetic field detected into electrical signals, which are in turn analyzed to identify areas where that magnetic field is changing, or in the majority of ILI cases, is ‘leaking’ out of the pipe wall due to a reduction in the wall thickness.

The signal is not a direct measurement like ultrasonics, but instead, the flux leakage is measured and the vendor utilizes algorithms to interpret and convert the identified signals into a length, width, and depth, which is then reported to the operator. These would be reported as areas of metal loss, which is generally corrosion, and provided with a percentage depth relative to the pipe wall thickness as well as length and width. The technique is considered an inferred measurement of metal loss since it’s an interpolation of the flux leakage.

Conversely, ultrasonics in wall measurement use a straight beam transducer to transmit/receive sound waves with a known velocity in the pipe material. The time for the return path reflection from the inside pipe wall compared to the reflection from the outside pipe wall provides a very accurate measurement of the wall thickness.

The Importance of Validating ILI Technologies

With any technology used, there is a requirement for validation of the technology, often referred to as a calibration dig. The process is discussed further in guidance documents and standards including API Standard 1163 – “In-line Inspection Systems Qualification” in the USA, and should be a necessary step within any pipeline integrity management plan to provide feedback for continuous improvement.

Tools are developed and tested in somewhat ideal conditions in most cases utilizing manufactured features as the basis for the generation of sizing algorithms. Unfortunately, real corrosion behaves very differently, and while ILI vendors utilize complex neural networks to create their sizing models, they can’t replicate the complex and interacting corrosion areas within the modeling since they are all unique. ILI tool vendors provide defect dimensions with both accuracy and tolerance. The accuracy related to depth for MFL tools is presented as + 10% as an example. That accuracy is also provided with a tolerance percentage, “with 80% confidence” for example. A call of general corrosion with a tool called depth of 45% may have an accuracy of +10% with 80% confidence based on specification. The sizing in this case of a feature called 45% by the vendor would be considered to be within depth sizing specification if the actual depth was between 35% and 55%. 

Additionally, specifications will vary with the defect type relative to the technology. Defects are categorized well by the Pipeline Operators Forum in their document, “Specifications and requirements for in-line inspection of pipelines” where they categorise features based on length and width dimensions relative to wall thickness. Categories are adopted throughout the industry with reference to the Pipeline Operators Forum (POF) dimension classification of General Corrosion, Axial Grooving, Axial Slotting, Circumferential Grooving, Circumferential Slotting, Pitting, and Pinhole.

As an operator, there is a duty to perform tool verification to validate what the tool is called, versus the real-world feature. This requires the completion of verification dig(s) where traditional NDT is used to verify specific features and compare them to the results presented by the ILI vendor. The vendor report will provide specific location information through chainage or GPS coordinates as well as references to upstream and downstream points to identify the feature(s) of concern within the dig site.

It may be difficult to confirm features for cross reference in more corroded pipes, so it is critical that the NDT vendor is familiar with the process for verification. It is equally important that the NDT vendor is equipped with the correct technology for the features being verified. That may mean pit gauge, laser scanner, pencil probes, mag particle, and so on for external features, but should include additional tools such as AUT for internal features, and cases of crack verification could include phased array and/or other technologies or techniques to verify. It can be difficult to identify and accurately locate internal features, so time and care should be taken before and during the verification process to align the location, clock position, and other identifiable features so that an accurate mapping of the target feature(s) is completed.

Learn More About How Ultrasonic Inline Inspection (ILI) Technology

Plotting Dig Verification Feedback

The feedback from the dig verification can be presented graphically in a unity plot where dimensions, (generally depth) and classification are plotted with “as found by ILI” versus “as found by NDT”. Adding the tolerance to the graph can quickly provide a visual representation of the accuracy of the calls, but will also show outliers. Any outliers should be discussed with the ILI vendor and in some cases the NDT vendor to confirm procedures and technology used for the verification.

Some better-equipped vendors, such as Onstream, can import NDT data directly to their proprietary software and show an overlay of both data sets which in some cases shows how features are both correctly or incorrectly aligned. Working closely with both the ILI and NDT vendors, the operator can provide invaluable feedback and in doing so have a better understanding of their pipeline condition, allowing them to act within their integrity management plan.

Onstream has thousands of verified anomalies which are used to further train its sizing algorithms including training and comparison of complex features. In addition, Onstream has the benefit in some cases of being able to access and split open cut-out pipe to reveal internal corrosion, which is then laser scanned for accuracy. This look inside is very beneficial, as field Automated Ultrasonic Testing can be difficult when investigating internal corrosion.

Looking Ahead: The Future of ILI 

Inline inspection continues to develop with tool specifications improving as electronics, software, and dig feedback are incorporated. Higher specification leads to better decision-making by operators, which improves safety and reduces operating costs. The feedback loop is a critical component in asset integrity management and allows vendors to push the technology forward.

ILI has been available since the 1960s and will continue to be integral to pipeline safety for the foreseeable future. It should not be considered to be the solution, but part of the overall integrity puzzle.