Published on 05-Jan-2022

Pulsed Eddy Current Testing (PECT)

Pulsed Eddy Current Testing (PECT)

When unseen corrosion, erosion and wear pose a threat, Pulsed Eddy Current Testing (PECT) is used to effectively assess and monitor assets.

Pulsed Eddy Current Testing (PECT) is used for the detection and assessment of the gradual thinning on ferromagnetic materials, due to failure mechanisms such as general erosion, wear and corrosion. Whilst PECT is not well suited for measuring the localised loss of material, such as individual pits, it can detect areas where clusters of pitting occur.

PECT is ideally suited for thickness testing on ferromagnetic materials with the wall thickness between 3mm and 75mm. PECT is effective on uncoated material but is most widely used on material with either coating or insulation, such as piping and pressure vessels, and also for detecting wall loss under marine growth on jetties and other marine installations.

PECT can be used to measure ferromagnetic base material thickness, through the following materials:

  • Concrete - with or without re-enforcement bars and, in some cases chicken wire.
  • Non-metallic coatings and insulation – for example paint, plastics, bitumen, epoxy, dirt, deposits, marine growth, Rockwool, with or without chicken wire and/or metallic protection (weather-jacketing or sheeting).
  • Aluminum sheeting
  • Other non-magnetic metal insulation covers excluding aluminum
  • Refractory
  • Fire proofing materials

PECT has a wide range of applications and ALS has specific expertise in the following areas:

  • Detecting flow accelerated corrosion on power station piping.
  • Through marine growth on jetty legs at loading areas and pipeline jetties.
  • Fireproofing on pressure vessels.
  • Detecting corrosion on lagged piping.
  • Detecting corrosion of lagged pressure vessels.
  • Scanning through very hot uninsulated components, such as valve bodies and high temperature heavy wall equipment.
  • Scanning through “corrosion blisters”.

Advantages of PECT

PECT is a semi quantitative screening method where the inspection probe does not require direct contact with the material being assessed. Inspection time is typically minimal and significant areas of thick insulation or fireproofing can be screened efficiently. 

  • Composite repair materials can be scanned through already occurred wall loss.
  • Scanning can be performed while a plant is on-line.
  • Results can be seen in real time.
  • Lagging or insulation does not need to be removed.
  • Marine growth does not need to be removed.
  • Inspections can be conducted using rope access, eliminating the need for expensive scaffold or staging.
  • Marinized probes are available for splash zone inspections.
  • Remote analysis is possible allowing for a very cost-effective inspection.

An additional advantage of PECT is its capacity to inspect through external corrosion product such as scale and blisters, however the thickness of the corrosion product should not exceed 25mm.

Corrosion Under Insulation

Corrosion Under Insulation (CUI) remains one of the greatest concerns for the integrity of insulated piping and vessels. When accessing a plant or asset, ALS utilises PECT to comprehensively understand CUI.

  • Common CUI scenarios that need to be assessed to ensure asset integrity include:
  • Areas exposed to mist overspray from cooling towers.
  • Piping close to steam vents.
  • Insulated piping close to deluge systems.
  • Carbon steel piping operating between -5°C to 120°C.
  • Dead legs and piping attachments through insulation.
  • Steam traced lines may have team leaks.
  • Damaged insulation.
  • Cracks in fireproofing.
  • Evidence of brown staining on insulation.

Flow Accelerated Corrosion

Flow Accelerated Corrosion (FAC) leads to gradual thinning of pipeline walls and is often associated with elbow bends. PECT is ideal for detecting FAC as it identifies areas of wall loss via a quick screening process and is suitable for pipelines with or without insulation.

Surprisingly, ALS inspectors have also detected FAC in straight sections of pipeline where the asset owner was not expecting to find it. This was discovered during inspection of pipe elbows where it was decided to extend the inspection along the adjacent straight sections.

Corrosion Under Marine Growth on Jetty Legs and Marine Structures

PECT today is often associated with the detection of CUI on pipelines and vessels, however from its early inception PECT has been primarily used for detecting corrosion under marine growth at the splash zone on marine structures such as oil rigs and jetties.

PECT is ideally suited to this purpose as it can send a signal through the marine growth, and any neoprene coatings without the need for it to be removed. In this situation, marinized (waterproof) probes are used and the inspection is often completed with rope access teams for easier access or divers where necessary. The rope access personnel or divers can place the probe on the inspection area and the technician can analyse the data in a separate location.

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Application Notes