Enabling Targeted Repairs On Ships With Pulsed Eddy Current

The marine environment is one of the most corrosive you can get.

Continuous exposure to salt water and salty air and heavy duty operations makes for an aggressive operating environment and given that many parts of ships or marine installations are under insulation or in hard-to-access areas, it’s challenging for technicians to locate defects before it’s too late to do cost-effective repairs or maintenance.

Ships are also key assets in many different fields including marine research, oil & gas, coastguards, freight, naval vessels to name but a few – and are high value assets.  The desire and motivation to maintain acceptable operating standards and prolong the service life of ships and their component parts is understandably a priority.

A key consideration however, is ensuring that repairs are targeted.  Technicians need to know exactly where the defects are and what has to be repaired prior to starting any repair work and incurring any costs.

Pulsed eddy current has proved its worth as a viable, fast and cost-effective non-destructive testing technique, notably because of its ability to test for corrosion under insulation (CUI) and for its suitability in field situations where the object surface is rough or inaccessible.

The following example of how pulsed eddy current (PEC) is used to target repairs on a ship’s deck plates highlights the effectiveness of the technique and why it has become an indispensable methodology in many industries where corrosion-detection is crucial.

Background

Deck plates play a vital role in the structural integrity of a ship and are crucial to the health and safety of the vessel’s personnel.  Corrosion on deck plates is a major concern because it is a common problem but one which often goes unnoticed until it is too late.

Furthermore, inspection/repair service providers often base their cost estimates on the surface area of the plates without knowing what lies beneath the coatings (which could be ceramic tiles, concrete, wood etc).  These linings need to be removed in order to reveal the location and extent of the problem – and once the service provider does so, the costs generally escalate significantly as the true nature of the problem and the cost of the solution becomes apparent.

Being able to assess the problem without removing any of the linings or coatings would be of enormous benefit from a budgeting and operational perspective.  Repairs could be targeted, downtime limited and preventative maintenance undertaken – all of which translate into massive savings and operational benefits.

Why PEC is so effective in this situation (and many others)

PEC technology is able to scan through non-magnetic coatings and insulation to detect corrosion underneath.  There’s no need for direct contact with the object or surface being tested, which means that accurate measurements can be taken without needing the coatings or insulation materials to be removed.

Proof of performance

Tests were done on the carbon steel deck plate of a decommissioned ship using the globally acclaimed Eddyfi pulsed eddy current solution Lyft® (which was awarded the Global New Product Innovation Award by Frost & Sullivan in 2016).

The plate was approximately 5.4mm in nominal thickness with a lining of 20.0mm and had welds and stiffeners on the one side.  Corrosion on the sides had pushed the lining upwards, causing it to separate from the steel plate by nearly 7cm on the left side.  Build-ups of ferrous oxide had also cause visible bulges in the lining.

Engineers used a small PEC probe and ran three different dynamic scans – one using clamps to close the gaps between the plate and the lining, one without clamps and one scan which was performed perpendicular to the stiffeners.

The engineers concluded from their results that scanning along stiffeners helped to maximise the detection of corrosion in close proximity to the stiffeners.  They also concluded that the data was not significantly affected by the gaps being open or closed.  The build-up of oxide also didn’t affect the data.

Other ships were inspected using the same process, with the conclusive results demonstrating that PEC is a viable and effective means of assessing the presence and extent of corrosion in deck plates.

This is clearly of crucial importance before any destructive repair work is commissioned and undertaken.  Put simply – it removes the costs associated with the unknown.

Benefits  

• No direct contact with the component under test is required
• Helps monitor the progress of corrosion over time
• Stiffeners can be used as landmarks, with welds and studs used as landmarks
• Facilitates a better understanding of corrosion mechanisms in ships’ deck plates
• Enables targeted repairs
• Enables fast and accurate assessment of the structural integrity of components that are likely to corrode without the need to remove any coatings or insulation
• Saves costs
• Helps avoid potentially catastrophic failure
• Enhances safety

Clearly, PEC technology is of significant benefit in the shipping industry as it enables targeted repairs on vessels – but field applications for the PEC go way beyond the marine environment.

PEC is a trusted method for NDT in a diversity of industries including civil engineering, petrochemical, oil and gas, power generation etc, and if you’d like to find out how your operation can benefit from this advanced technology, have a chat to the experts at Nexxis.

Nexxis is a leading supplier of technical equipment in Australia and they carry a wide range of NDT and remote visual inspection (RVI) equipment, including the Eddyfi Lyft and the Splash Zone PEC Probe . For more information, please contact us.