Unpiggable Pipelines & ILI Alternatives

For many pipelines the use of In-Line intelligent pigs is not possible, these are considered to be “unpiggable pipelines”. Furthermore, pipeline operators are increasingly looking for alternative strategies to ILI to allow increased production time and decrease the risks associated with ILI inspections of more challenging pipelines.

For these cases, alternative inspection strategies are required. Identifying suitable inspection techniques and strategies is becoming an increasing concern as a pipeline system starts to show age and in many cases, exceed their design life.

In-Line Inspection Alternative Techniques

Quantitative pipeline assessment.

When it comes to inspecting unpiggable pipelines, our services provide the best alternative to in-line inspection. Our technology is designed to provide comprehensive and accurate data without the need for in-line inspections. Our services are reliable and efficient, allowing us to inspect pipelines faster and more effectively than traditional methods.

Unpiggable pipeline inspections use advanced x-ray imaging technology to provide a detailed analysis of the interior of the pipe and surrounding area. This provides an accurate gauge of the condition of the pipe and any potential points of corrosion or damage. 

Our services also include ultrasonic testing (UT) to supplement the x-ray inspection, providing further information on corrosion rates, wall thickness measurements and other valuable data.

In addition, our technicians are experienced in performing manual inspections using borescopes, where access ports are available, allowing for a more hands-on approach to inspecting walls in areas not reached by x-rays or UT scans. 

Techniques and Deployment Tools

Sonomatic unpiggable pipelines tool.

In the case of unpiggable pipelines or alternative strategies to ILI, a variety of techniques and deployment tools are often required. Typically inspection strategies fall into two approaches, an external screening approach covering as high a percentage of the pipeline as possible, or a targeted inspection approach identifying areas most susceptible to defects and applying high-resolution techniques.

Regardless of the approach taken or inspection requirement, Sonomatic can provide the correct pipeline inspection tool and techniques to fit the requirement. Sonomatic pairs our subsea inspection capability with a depth of NDT knowledge and integrity capability, to assist clients with picking the best strategy and techniques for meeting the requirement on unpiggable pipelines.

Benefits of Unpiggable Pipeline Inspections

Quick and Direct Assessment: Utilizing advanced subsea Computed Tomography imaging technology for unpiggable pipeline inspections allows for quick and efficient assessments without having to physically enter the pipe itself or remove sections for inspection. This reduces downtime and costs significantly compared to traditional methods such as manual inspections or even full-scale excavations which can take much longer.

Identify Problem Areas: With ultrasonic testing, we can quickly identify areas that may be prone to corrosion or other issues that could lead to leaks or pipe failure, leading to improved safety and avoiding costly repairs down the line due to preventative maintenance early on.

Ultrasonic testing can also be used to measure the wall thickness of a pipe – as well as the pipe diameter range – helping us identify areas that may need reinforcement or repairs due to corrosion or other wear-and-tear over time. This is an invaluable tool for detecting any anomalies before they become serious issues and helps us prioritize maintenance according to the risk of failure.

Reduce Costs: By combining different methods such as manual inspections with advanced imaging technologies, our technicians can provide a comprehensive overview of what’s going on inside an unpiggable pipeline without having to resort to costly excavation techniques of other existing technologies which can often be inefficient due to their invasive nature.

Non-Destructive: Ultrasonic testing is non-destructive which means you don’t have to worry about damaging pipelines during inspections, reducing the need for costly repairs post-inspection and ensuring our pipelines remain safe and functional at all times. This makes it considered by some to be the most efficient method of inspecting unpiggable pipelines.

Frequently Asked Questions

Ultrasonic corrosion mapping involves scanning the pipeline to determine the minimum remaining wall thickness for each position and can be achieved using an advanced automated ultrasonic tool The systems deployed, produces comprehensive high-quality data that can be displayed in different views to easily identify and/or verify any areas of concern. Sonomatic Inspection Management Software (SIMS) is used to generate 2D and 3D thickness map composites to improve efficiency in data management during the collection phase, and assists in semi-autonomous data analysis and reporting.

TOFD is a method of accurately sizing and monitoring the through wall height of in-service flaws.It is effective for weld inspection flaw detection irrespective of the flaw type or orientation. TOFD doesn't rely on the reflectivity of the flaw, but uses diffracted sound initiating from the flaw tips. TOFD main advantage is that it has a through wall height accuracy of +/- 1 mm, and a crack growth monitoring capability of +/- 0.3 mm, on defects of all orientations. 

DRS is a proprietary technology developed by Sonomatic using frequency-based ultrasonic wall thickness measurements. It is a corrosion mapping technique that applies a broad range of low ultrasonic frequencies (<1 MHz) to penetrate challenging coatings such as composite repairs, PE and Neoprene, and excites the natural frequencies of vibration of the underlying steel. The DRS probe raster scans over an area of interest and collects response signals. Advanced signal processing algorithms have been developed to extract the vibration frequencies and map the wall thickness profile.

Full matrix capture (FMC) is a data acquisition strategy that allows for the capture of every possible transmit-receive combination for a given ultrasonic phased array transducer.

InspeCT™ is Sonomatic’s proprietary subsea computed tomography system designed to eliminate the requirement to remove protective pipeline coatings, specifically concrete weight coating, to evaluate common pipeline integrity challenges including corrosion under insulation/coating, internal pitting & corrosion, degradation of internal linings & corrosion-resistant alloys, and detection & sizing of internal build-up of deposits and scale.

EMAT technology is performed from top-of-line and has the capacity to detect internal and external corrosion on subsea pipelines with NWT <15 mm with coating thickness up to 4 mm. The technique does not require direct coupling as the input and received signals are generated by electromagnetic responses. This screening technique provides details of the lateral extent of corrosion with banding to indicate the through-wall severity level.

Multiskip is an ultrasonic rapid screening technique for corrosion and erosion detection on subsea pipelines ≥4” diameter. It uses two transducers mounted on wedges in a pitch-catch to send angled shear wave beams through the pipe wall by skipping multiple times off the ID and OD surfaces. The system is capable of high-speed, high-resolution data collection. For corrosion, loss of signal amplitude, reduction in signal arrival times, and changes to signal shape are used to provide qualitative and quantitative information.

GWT is primarily a screening method used only to establish if there are any corrosion issues that need further investigation. Long lengths of difficult-to-access pipe can be examined from a single location with minimal preparation and while the process is online. GWT systems use low-frequency guided ultrasonic waves that propagate along the pipe wall and are designed for rapid screening of long lengths of pipe to detect external or internal corrosion.


SEF is also an electromagnetic technique performed on top-of-line and used for localised corrosion detection of the internal and external surfaces of subsea pipelines. SEF inspection is a comparative NDT method meaning that all results obtained during the inspection are compared and evaluated against results from the calibration scan.

SEF provides qualitative through-wall sizing information with results sentenced in four sizing ranges 0-19%, 20-39%, 40-49%, >50%. Once an actual SEF defect indication in the area inspected is verified and confirmed with ultrasonic testing, the measurement can then be used to adjust the final calibration to aid the accuracy of the analysis.

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