Corrosion Inspection Techniques
Corrosion inspection on ferrous metals has long been a challenge. Assets – especially in industries, such as Oil & Gas, Petrochemicals, and Mining, are subjected to 24/7 use, as well as extremes of temperature and pressures.
This makes degrading metal, caused by corrosion, inevitable. Inspection and monitoring is essential to prevent sub-optimal operation, excessive operating costs, danger to personnel, unnecessary environmental emissions and more. There are various corrosion inspection techniques available, with the chosen type being dictated by many needs, including:
- The type of asset
- The size of the asset
- The location of the asset
- The asset environment
The following are the most common types of NDT methods that can carried out using advanced inspection tools.
- Ultrasonic testing (UT): A mainstay of asset testing, UT measures the thickness of a metal wall with short ultrasonic pulse-waves. It can also be used on other materials, such as concrete and wood. The returned data shows the amount of material that’s been corroded in relation to non-corroded areas that surround it.
- Magnetic Flux Leakage (MFL): This uses magnets to show locations where the magnetic field is ‘leaking’. Such areas are indicative of damage – in other words, corrosion.
- Acoustic Emission (AE): Similar to UT, this also uses ultrasonic waves. However, with AE, the waves are introduced from a localised source within the material, as opposed to a tool held to the outside of the asset.
- Radiographic testing (IR): This uses electromagnetic radiation (gamma rays and x-rays) to create an image – similar to how an x-ray is produced for examination of the human body.
The latter is often used within the aviation and motor industries, allowing them to examine elements of the vehicle that aren’t visible to the naked eye. However, it’s also a useful type of testing for any plant with pipes, boilers and/or welding, such as Oil & Gas.
AE testing is highly effective but comes at a high price. Historically, its use has been limited to the inspection of expensive structures, although advancing technology is gradually making the method more affordable.
This leaves us with the two most popular method: UT and MFL. However, despite their accuracy and commonplace use, there are still many challenges. The most pressing of these is the ability to get up close enough to the assets to carry out the task.
Typically, such testing requires humans to bring inspection tools to the asset, so allowing the method of testing to travel through the material and the data to be returned. The problem with this is that many assets are difficult (or impossible) to reach. Examples of this include:
- Tanks and storage areas with non-oxygen atmospheres
- Having to work at height – both internally and externally
- Assets with complex internal geography
- Assets with pipework
This is where remote inspection tools and advanced technology are revolutionising the field of NDT. Robotic platforms, such as Magneto, offer semi-autonomous designs that negates the need for human inspectors to enter confined spaces to carry out UT inspections. Elios 3 is a custom-built arial inspection drone that allows users to gain advanced visual and thermal data of interior assets.
These are but two examples of how technology is answering the challenge of corrosion inspection and maintenance. Another new-to-the-market tool is the PipeScanner HD MFL tool, designed for ease of use, accuracy and fast corrosion monitoring, and requires minimal training to use.
As technology advances, the ease of corrosion monitoring increases – and along with it the ability for asset and plant managers to conform to environmental requirements, increase the safety of their workers and reduce costs for their shareholders.
