CASE STUDIES

Underdeck Inspection: PEC Technique

 

 

Overview

AISUS carried out an inspection using the Pulsed Eddy Current (PEC) technique on the underdeck of an offshore platform, inspecting the East and West accommodation module seal plates. The purpose of this inspection was to obtain visual and wall thickness data to identify any anomalies. Visual inspection, ultrasonic testing and PEC Technique inspection was conducted via a magnetic crawler system.

Requirements

The inspection aimed to achieve three main objectives:

  • Remote Visual Inspection: Assess the external surface condition of the accommodation floor seal plates, paint condition and identify any defects.
  • Ultrasonic Testing (UT): Measure plate thickness using UT to establish a reference for plate thickness.
  • Pulsed Eddy Current (PEC) Technique: Conduct PEC inspection to measure the remaining material volume.

Solution

The PEC technique is based on electromagnetic induction. A coil within the probe is excited with a current pulse, generating a primary magnetic field near the probe. When the metal test specimen is in proximity, it induces electrical currents known as ‘eddy currents’ inside the probe.

The signal received is displayed as a function of time, creating ‘C-Scans’ (colour plots) with the full waveform saved for future reference.

The underdeck of this platform is a difficult area to access, making human access challenging. The PEC solution excels in delivering fast and effective results without requiring any preparation or cleaning beforehand. It can inspect through thick coatings and marine growth.

 

Approach

The inspection was executed using an encoded magnetic crawler, which transported the PEC technique probe across the seal plate surface. The inspection collected data points in a predetermined grid, once in every 150mm x 150mm.

A safety line was installed across each seal plate to support the 12kg crawler in case of magnet failure. The safety rope also acted as guidance for keeping the crawler on a straight track for inspection.

Square edges affect the PEC technique signals therefore a boarder of minimum 50mm must be used.

Results

General wall lose was observed along the edge of the east plate, with a minimum recorded measurement of 53%. Additionally, significant wall loss was detected around the drilling holes, with a minimum reading of 70%.

Furthermore, localised patch corrosion was identified around the weld areas, with a minimum reading of 70%.

Benefits

  • Eliminates the need for cleaning preparation
  • Measures through thick coatings
  • The PEC inspection technique is highly efficient for corrosion screening, even in challenging areas.
  • Quantitative data produced allows for accurate assessment of defect severity.
  • Data supports informed decisions regarding asset integrity and maintenance strategies.
  • Comprehensive data report with PEC technique data in C-Scan format along with images captured from the visual inspection.

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