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, operators are increasingly looking for alternative strategies to ILI to allow increased production time and decrease the risks associated with ILI inspection.

For these cases, alternative inspection strategies are required. Identifying suitable inspection techniques and strategies is becoming an increasing concern as pipelines age and in many cases, exceed their design life.

Techniques and Deployment Tools

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 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.

Screening Techniques

Sonomatic unpiggable pipelines tool.

EMAT Deployment (SH and Lamb Wave)

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.

Guided Wave Testing (GWT)

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 on-line. GWT systems use low frequency guided ultrasonic waves that propagate along the pipe wall and is designed for rapid screening of long lengths of pipe to detect external or internal corrosion.

Saturation Eddy Current Fast Screening (SEF)

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.

High Accuracy Verification Tools

Ultrasonic Corrosion Mapping

Ultrasonic corrosion mapping involves scanning the pipeline to determine the minimum remaining thickness for each position and can be achieved using conventional UT probe or a PAUT probe. The systems deployed produce 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.

Time of Flight Diffraction (TOFD)

TOFD is an industry norm for pipeline weld inspection. This ultrasonic technique is the best method for defect detection and accurately sizing & monitoring the through-wall height of weld defects.

Phased Array inclusive of Full Matrix Capture (FMC/TFM)

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.

Dynamic Response Spectroscopy (DRS)

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.

InspeCT (Computerized Tomography)

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 an internal build-up of deposits and scale.

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