Structural Inspection

Sonomatic has a strong track record of inspection and related integrity activity in support of Structural Integrity Management. Our work in this area has tended to focus on safety and business-critical applications. The aim is to provide clients with accurate and reliable information on which to base their integrity plans and decisions.

Subsea structures can be subject to a variety of integrity threats both internal and external. Subsea structures require a variety of options in terms of deployment and access solutions.

Sonomatic is well suited with a wide range of inspection techniques to provide the best solution for the integrity threat present. Furthermore, Sonomatic has a wide range of existing ROV and Diver solutions that can meet most access requirements. When a custom access solution is required, Sonomatic has a depth of experience delivering from initial concept to field execution on custom solutions for structural inspection requirements.

In need of a structural inspection for your project? Get in touch with us today to find out more.

An image of a Sonomatic Subsea ROV performing a subsea inspection
Subsea Assets for Internal and External Inspection:
  • Caisson services
  • Riser services
  • Conductor services
  • Pile services
  • Well head services
  • Subsea storage tank services
  • Subsea tree services
  • Manifold services

Subsea Structural Inspection Techniques

Deployable techniques:
  • Ultrasonic Corrosion Mapping
  • Time of Flight Diffraction (TOFD)
  • Phased Array inclusive of Full Matrix Capture (FMC/TFM)
  • Pulsed Eddy Current (PEC)
  • Dynamic Response Spectroscopy (DRS)
  • Automated Shear Wave Pulse Echo
Solutions for:
  • Internal and external corrosion
  • Internal and external cracking

Subsea Structural Inspection Applications

Corrosion Inspections and Mapping
  • Corrosion can be a serious problem for any project, with it being capable of causing serious damage to various structures on a project even during the building phase. Our inspection techniques are capable of detecting and mapping areas that are corroded before they become major problems.
Crack Detection
  • A crack in the structure of any project can mean potential disaster both from a monetary and personal standpoint. The numerous techniques Sonomatic can deploy are able to find and identify bot internal and external cracks while staying in accordance with appropriate health and safety regulations.

Cleaning & Corrosion Mapping Inspection of Large Subsea Oil Storage Tank

Sonomatic adapted existing subsea inspection equipment (MAG-Rover), to enable simultaneous water jet cleaning and ultrasonic PA data collection on a subsea structure. A new challenge for Sonomatic with an intense development process due to vessel operational timeframes. We completed the task in hand, successfully with all stakeholders very satisfied with the outcome.

For more information, you can download the case study featured at the bottom of this page.

Check out the MAG-Rover put into action below:

Frequently Asked Questions

Automated 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.

Time of Flight Diffraction (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's 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.

Dynamic Response Spectroscopy (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.

Pulsed Eddy Current (PEC) is a comparative technique whereby advanced processing of the eddy current signal decay and comparison with a reference signal, allows for the determination of the average wall thickness (AWT). This fast screening method allows for the assessment of the general condition of structural steel and is best suited for general corrosion type defects in subsea pipelines. A major benefit of PEC is its ability to inspect through concrete weight coating, challenging coatings and marine growth.

Angle shear wave methods are widely used in NDT and in most applications the probe is manually manipulated. There are, however, significant benefits to automating the process, both in terms of probe manipulation and data collection. The benefits include the following:

  • Consistent performance with minimised human factors effects
  • Substantially improved probability of detection (POD)
  • Improved sizing capability
  • Accurate positional control
  • Accurate position information for each scan
  • Full recording of all data for more detailed analysis
  • Reliable repeat comparisons

Automated shear wave pulse echo is used for a variety of applications, some  examples are listed below:

  • Inspection of welds to detect and size planar flaws.
  • Inspection of corrosion-resistant alloys for stress corrosion cracking.
  • Inspection of corrosion-resistant alloys for chloride pitting.
  • Inspection of materials in wet H2S service for vertical cracking elements.

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.

Alternating Current Field Measurement (ACFM) is an electromagnetic technique for the detection and sizing of surface-breaking indications. It works on most metals, does not require direct contact and works through various thicknesses of coatings. ACFM can accurately detect and size linear indications both length and depth. It is also easier to use on complex geometries such as nodes and nozzles.

A phased array is a unique ultrasonic probe consisting of a group of transmitters or receivers, allowing for precise control of sound waves. When used as a transmitter, the timing of element activation creates interference that can shape and angle the beam. As a receiver, the time differences between pulse arrivals at each element provide information about the pulse source's location. Similar to how our ears work, phased arrays can pinpoint sound directions. Unlike traditional twin-crystal probes, phased arrays adjust signal phases for desired beam angles. However, their performance relies on the number, size, and spacing of elements, requiring specialised signal processing equipment. Phased arrays are widely used in radar, sonar, and medical applications but face challenges in NDT ultrasonics due to metal penetration and wave mode issues.

Ultrasonic testing utilises sound waves to detect corrosion within materials. This NDT technique utilises array transducers that pulse elements in a sequence called phasing.

Eddy Current Testing (ET) is used to measure the intensity of electrical currents in a magnetic field. Eddy current testing utilises AC current in a coil near or around a specimen, inducing circulating eddy currents in the material's surface. Flaws and material differences affect these currents, altering the coil's current via mutual induction. Flaw detection relies on measuring electrical changes in the coil, often focusing on voltage changes. Key factors influencing eddy currents include specimen conductivity, magnetic permeability (for ferromagnetic materials), coil-specimen distance, AC frequency, and dimensions. Calibration on test specimens is common, and eddy current testing is highly sensitive to flaws. Equipment ranges from basic meters to advanced computer-programmed systems, with applications including crack detection, component sorting, and metal quality control.

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