Pulsed Eddy Current Testing (PECT) 

 A rapid screening corrosion method for average thickness assessment of insulated ferrous pipelines, tanks, vessels and other components.  

Benefits

• Thickness measurement (Corrosion under Insulation) without insulation removal
• Corrosion assessment of steel embedded in concrete or asphalt
• Corrosion of steel submerged in water (marine conditions)
• Fast (2m/min with 20mm scan width or 1 second/spot)
• Accurate (±10%)
• Digital plan imaging
• Huge cost savings by not removing or reinstating insulation
• No surface preparation needed, saving time and money
• More complete inspections reduce asset downtime

Capabilities

• Hot or cold test surfaces up to 550°C
• Through up to 150mm thick insulation
• Through any non-conductive insulation - natural fibers, asbestos, fireproofing, coatings, ceramic, concrete, brick, foam, wool, thermocol, bitumen, etc
• Through galvanised, stainless, aluminium, cladding or weather jacket
• Through chicken or hog wire reinforced insulation, straps or protective and polymer coating
• Through any corrosion scabs, blisters etc. No surface preparation needed, minimising risk and cost.
• Measure thickness from 4 to 65mm on pipes above 75mm diameter or vessels or spheres or support legs.
• No need for scaffolding. Remote control inspection using extension arms up to 4.6m height.
• Battery powered instrument. Perfect for remote locations.
• Absolutely safe. Unlike radiographic methods, involves no X-Ray or Gamma Ray radiation.
• Probes are waterproof for marine applications.
• 30m long telescopic extension arm for measuring underwater. Perfect for piers at ports and bridges.

Pulsed Eddy Current - PEC testing is a corrosion assessment; non-destructive test method utilised primarily on insulated or enclosed ferromagnetic materials. Corrosion survey or a wall loss measurement can be performed without a need of removing insulation, cladding, asbestos, fireproofing, concrete or protective coating material from the test surface. Pulsed Eddy Current - PEC testing is a spot measurement technique which provides average thickness at the test location.

Pulsed Eddy Current testing also commonly known as PEC is one of the eddy current test methods wherein pulses of low frequency eddy currents are induced in the test material. Similar to other surface eddy current methods, in Pulsed Eddy Current testing (PECT) a probe sensor is placed on top of the insulation layer. The material covered under the insulation can be kept live and hot up to 550 degrees Celsius. Low frequency pulsed eddy currents are induced in the test material. The duration of sustained eddy currents in the test material is measured and a relative thickness or percentage remaining wall thickness is calculated.

Corrosion under insulation CUI is one of the most undetectable corrosion mechanisms that can affect the integrity of the plant or asset and may not be noticed until the degradation has occurred beyond risk mitigation. Corrosion under insulation CUI, as the name suggests occurs under the insulation layer which is not readily visible to the plant operators. Pulsed Eddy Current - PEC testing can provide wall thickness measurements through any non-ferrous insulation materials such as natural fibers insulations material, calcium silicate, titanium based coatings, ceramic paint, concrete, brick, foam, wool, thermocol, bitumen, dirt, sludge, etc. It can also measure through galvanised, aluminum and stainless weather sheeting.

Ideal Applications:

• Detection of corrosion under insulation CUI degradation
• Detection of internal flow induced erosion or corrosion
• Wall thickness measurement of tanks or pipe-rack without additional cost of scaffolding work or use of elevated working platforms
• Wall thickness measurement of excavated pipelines without coating removal and without sand blasting or surface grinding.
• Most ideal on insulated, cladded, covered material surface. Subsea and splash zone inspection
• Pulsed Eddy Current - PEC testing on high temperature surface without shutting down plant
• Inaccessible test surface e.g. covered with asbestos or brick wall or sand covered
• Hot or cold insulated pipelines, vessels, equipment, columns, storage tanks, concrete coated sphere legs
• Insulated pipes above 100mm diameter or vessels or spheres
• Pulsed Eddy Current - PEC testing can measure wall thickness from 4 to 65mm with repeatable results within the range of ±10%.

Limitations:

• Thickness readings are average thickness under the sensor footprint measured in % remaining wall.
• PECT measures average thickness at the test location (probe footprint) which varies between 35-200mm depending on insulation thickness, clad material and the wall thickness of the test material. Thickness readings are average thickness under the sensor footprint (1.8 times the footprint) measured in % remaining wall. 
• Pulsed Eddy Current - PEC testing cannot detect a small isolated pit
• The edge effect impacts PEC measurements when a probe nears geometry variations such as nozzles, flanges, or the end of a structure. Measurements begin to vary from a distance of one Footprint from the center of a probe’s coils.
• Difficult to use on elebows smaller than 200mm diameter
• Current version of software is unable to discriminate near side and far side defects.
• Flaws smaller than the averaging area of the probe will be undersized.

PECT Comparison with other NDT methods (UTT & RT)

Notes –

1. PEC measures structural (volumetric) wall loss (saturation and decay of eddy current within the steel volume) whereas UT is only localized thickness assessment by measuring time of flight of reflection.

2.  Radiographic test results can be non-interpretable due to  poor radiographic image on some vessels or pipes due to vibration or flowing fluids or high density fluid contents.

3. Radiographic images may not be obtainable on large diameter vessels or pipes due to the longer distance between radiation source and radiographic capturing devices (film or sensors)

Abbreviations:

PECT – Pulsed Eddy Current testing using Eddyfi Lyft

CRT – Computed Radiographic testing

DRT – Digital Radiographic testing

RT – Radiographic testing (conventional film based)

UTT – Ultrasonic thickness test using systematic or unsystematic spot measurements

Frequently Asked Questions

FAQ 1 – I need to measure wall thickness of old bridge structures without removing lead paint coating. Can you perform Ultrasonic thickness test over lead paint coating?

Advice – As per most of the International Standards and Codes, Ultrasonic testing shall be performed on a ground bare metal surface for effective transmission of ultrasound in to the material under the test and to obtain accurate repeatable test results. For a general purpose, Ultrasonic testing may be possible if the coating is completely adhered to the metal surface.

If lead paint is a concern, then alternative thickness measurement such as Pulsed Eddy Current testing (PEC) can be performed without removing lead paint or any other coating. PEC does not require any surface preparation or coating removal.

FAQ 2 – I have been informed that PEC cannot detect pitting. So why should I apply PEC?

Advice – This is not 100% true. PECT cannot detect an isolated pit. But it can detect cluster of pitting. In UT, asset owners nominate to perform random or 100mm grid spacing UTT. Most of the time the probe is twin crystal, 10/2 diameter probe. Hence in a 100x100mm grid, ONLY 0.78% of the surface area is tested. (79mm2 out of 10,000mm2). This means there is 99.2% probability that UTT will not detect an isolated pit or even cluster of pitting in a 100mm grid pattern. Also, UTT depends on the flatness of the back wall. Several published papers indicate that on most occasions, UTT measures incorrect corroded minimum remaining wall thickness because the reflecting surface is either not perpendicular to the compression waves or the sound simply dissipates due to rough surface.

Whereas in PEC, the smallest footprint is 35mm diameter, and because of its speed, 100% of the surface area is scanned without coating removal. Hence, if there is a considerable loss of wall as a result of an isolated pit or a cluster of pits which can affect the fitness for purpose pressure vessel calculations then PEC will 100% indicate volumetric thinning.

FAQ 3 – I have been informed that PEC cannot measure thickness of steel when the surface temperature is 550⁰C. So how can I apply PEC in my plant?

Advice – PEC can measure wall thickness of ferrous steel having surface temperature up to maximum 550⁰C and adequately insulated so that the surface temperature on the cladding surface is limited to 70⁰C maximum. It should be noted that alternative test method such as conventional ultrasonic testing cannot be performed at such a high temperature.

If the cladding (weather jacket) surface temperature is exceeding 70⁰C then a ceramic shoe can be added at the bottom of the probe and perform PEC.  It should be noted that it is not a safer practice to work at such a high temperature.

FAQ 4 – What is the extent of traceability and repeatability of PEC as compared to UTT & RT? Is it operator dependent like UT & RT?

Advice – UTT & RT are too much operator dependent and hence the probability of the traceability of results is uncertain.  Whereas in PEC, operator’s involvement is only to place a probe on the cladding after the Level 3 has entered all essential parameters. The instrument provides assessment results storing of results, reporting of data, colour pelleting, etc.

FAQ 5 – What is the smallest flaw PEC can detect?

Advice –PEC is an average wall loss measuring technique and is ideal for screening and measuring general corrosion through insulation, cladding or other non-conductive coverings. For detection of localised damage such as pitting or cracking, LMATS ’ NDT experts and inspectors can advise on the most appropriate techniques, which may include eddy current array (ECA) testing for detection of linear discontinuities, phased array ultrasonic testing (PAUT) for the detection of small pits and wall thickness, or one of the many other available NDT methods

 FAQ 6 – I need to excavate underground pipeline for wall thickness measurement, but I don't want to remove Coating or perform grinding  on live pipeline wall surface for Ultrasonics. Can you measure wall thickness? 

Advice –Ultrasonic requires sufficient ground flat surface for the transducer coupling for sound transmission. PEC works on Electromagnetic principle which does not require direct contact. Hence PEC can measure wall thickness on a live pipeline without the need of surface grinding and without the need of coating removal.

FAQ 7 –My pipeline is covered under insulation or concrete? Can LMATS detect weld location using any NDT method?

Advice – LMATS can find weld location on your insulated pipe or vessel using PEC - Pulsed Eddy Current test method.  As compared to Radiography, exclusion zone required and multiple exposures required, PEC is a single person operation and it can be completed within few minutes on site.

Expertise:

Compared to conventional ultrasonic testing, Pulsed Eddy Current testing (PECT) instrument and sensors are complex and expensive. This test method requires highly trained, skilled and experienced technicians. 

LMATS engages certified and experienced engineers to provide Pulsed Eddy Current - PEC testing.

LMATS offers PEC – Pulsed Eddy Current testing and inspections from our Melbourne, Sydney, Brisbane, Albury laboratories and Newcastle (Australia), Malaysia and India workshops.
LMATS regularly performs PEC – Pulsed Eddy Current testing in VIC -Victoria, NSW - New SouthWales, QLD - Queesnland, QLD - Brisbane, SA - South Australia, TAS - Tasmania, NT -Northern Territory, WA - Western Australia and some of the countries aroung the world.

To find out more about LMATS PEC – Pulsed Eddy Current testing Advanced NDT Tracable Inspection Capabilities simply call us or contact us +61 3 9399 9199 or via the form