Spotlight on: Non-Destructive Testing (NDT)
Brookes Bell has been offering non-destructive testing (NDT) services for some time to identify and assess the extent of corrosion on the deck of a vessel as well as a range of other flat steel structures. Until recently, we’ve used conventional eddy current testing which involves the use of an alternating-current to generate a changing magnetic field within the steel being inspected. The magnetic field produces eddy currents which are monitored and interpreted to identify any defects, such as corrosion.
This is a useful and widely used testing method but it does come with limitations. The decks of most vessels are heavily coated with specialist insulation and paints. These need to be scraped away before the test can be applied. Because of this, testing is often confined to just a few sample areas which are used to make a global strength calculation and an assessment of the overall condition of the steel.
At Brookes Bell, we are working to introduce an enhanced NDT regime known as Pulsed Eddy Current (PEC) testing. The same principle is applied but PEC methods are able to penetrate protective coatings and insulation material allowing a much more rapid and cost-effective test to be undertaken. Additionally, a PEC test uses a seven-channel probe (standard tests use a single channel probe) which means more than 50 times the number of areas can be scanned in a similar time frame to give a more complete and accurate picture of the overall condition. PEC is not unique to Brookes Bell, but we have married the technology with a comprehensive analysis and reporting tool that includes 3D imagery. This allows tolerance levels to be set and repeat inspections to be conducted to closely monitor change and the pace of any deterioration. This ensures that steel is not replaced unnecessarily.
We are currently undertaking a Probability of Detection (POD) process to demonstrate that PEC is capable of accurately detecting and mapping the status of a steel deck. Our findings are soon to be independently assessed and verified by Lloyd’s Register which will give us class approval to offer this new, enhanced testing regime to a number of our customers. The next step is to gain wider approval from all IACS member class societies.
This is a significant step forward in NDT testing which will result in a more accurate, more rapid and more cost-effective assessment of the condition of flat steel structures.
More information is available here
- Arron Jackaman