Acoustic Emissions (AE) is a highly underutilised Non Destructive Testing (NDT) method in Western Australia. For decades this technology has been used on Offshore Oil rigs, Aerospace facilities and other industries but it has not penetrated the Australian infrastructure market as well as it has overseas. This is mostly due to a lack of knowledge both of its possible uses and reliable application by NDT companies.
Recently Rapallo and our technology partners have implemented world leading technology, software and AE equipment to better monitor critical in-service pressure vessels for our clients. But first a quick reminder of just what AE is;
Acoustic Emissions Condition Monitoring – NDT
Acoustic Emissions (AE) testing is a method for examining behavior of materials deforming under stress. Basically – like many people, when materials are under stress they talk. With Acoustic Emissions testing or monitoring, you can “listen” to the sounds of cracks growing, fibres breaking and many other modes of active damage in stressed materials.
The Acoustic Emission Non Destructive Testing (NDT) technique is based on the detection and conversion of high frequency elastic waves into electrical signals. This is accomplished by directly coupling piezoelectric transducers on the surface of the structure while under test and loading.
Sensors are coupled to the structure, and the output of each sensor (during structure loading) is amplified through a low-noise preamplifier, filtered to remove any extraneous noise and furthered processed by suitable electronic equipment.
This all boils down to a very sensitive monitoring system that is able to triangulate where active deformation of your asset is occurring. This includes crack propagation or growth as well as active corrosion.
New Machine Learning Algorithms
Rapallo’s together with its Technology, Research and Development partners have developed world first adaptive learning software to more effectively interpret AE data. Using leading edge algorithms, our team has developed software that analyses raw AE data in near real time while also adapting to the asset being monitored. This has massive implications, allowing for real time AE monitoring without having an experienced (and costly) AE data analyst watching a feed constantly.
Current systems send alerts when abnormal activity is detected but still require an analyst to be on call to analyse such events. With this software, the AE data that is received is constantly analysed and compared to what is ‘normal’ for that asset. This is what we call Machine Learning. Over time, the software learns what AE activity is normal for your asset and what activity is a potentially catastrophic crack or deterioration.
Traditionally this learning of normal activity is attained by monitoring an asset under varying load conditions and manually comparing AE data against the asset’s load/pressure/temperature cycles or SCADA data. These new Machine Learning algorithms have automated this process, creating a more cost effective and accurate solution that doesn’t require in depth AE data analysing experience.
Finite Element Modelling and Analysis Tools
Finite Element Analysis (FEA) has been used for decades as a design tool to determine stresses in structures, vessels and other assets before they are constructed. To do this FEA requires a model of your asset to be created, called Finite Element Modelling (FEM). While FEA and FEM are excellent tools for theoretical design, when an asset is used for its design purpose in the real world there are often production, design and environmental impacts that were not considered. By monitoring the asset with AE and comparing the areas of real world stress indicators with the design parameters the theoretical design can be verified. This allows for better future design and a much better understanding of how your asset reacts to how you use it.
Over the years Rapallo has found (and I’m sure you have too) that an easy to understand visual representation is a lot more effective than numbers to convey lots of data. Traditionally AE data is presented as what is known as a ‘Heat Map’.
A Heat Map is a 2D representation of your 3D asset showing acoustic activity in varying amplitudes using a standard scale of colours. Our team have taken this one step further by overlaying the AE data on an easy to understand 3D Finite Element Model.
The added advantage of this method is that the Finite Element Model can be used to analyse the stresses the asset undergoes in normal operating conditions and compare this to what is being detected by the AE system. Combined with the Machine Learning software above this is a powerful condition monitoring tool far ahead of any other product on the market for AE today.
Benefits of Using Acoustic Emission (AE) testing
- Shut down is not required. Plant remains in normal operation. Natural operational cycle provides the dynamic load
- Removes the need for confined space entry which reduces the risk to personnel health and safety
- 100% Structural Integrity survey of the complete shell compared to partial examination by traditional NDT methods, including visual inspection. Detecting crack initiation, growth and location. A crack only needs to propagate by 100 – 200 μm in ferrous material in order to generate the burst of energy large enough for detection.
- Potential to extend the interval between shutdown inspections as per AS 3788
- Risk mitigation by periodic or continuous condition monitoring
- Full removal of cladding and insulation is not required
- Improved awareness of the shell integrity, early warning of potential integrity issues
- Targeted repairs and preventative maintenance directed to specific locations that otherwise will not be known
With Acoustic Emissions testing small-scale damage is detectable long before failure, saving you time, money and minimising risk to safety.
Where is Acoustic Emissions (AE) used?
- Pressure equipment: This technique has become a reliable and standard method of Non Destructive Testing (NDT) for pressure vessels. Acoustic Emissions (AE) is used to monitor flaws, corrosion and leakage in pressure vessels, LPG tanks, piping systems including transmission pipes and steam generators
- Petrochemical and chemical: storage tanks, reactor vessels, offshore & onshore platforms, drill pipe and pipelines
- Civil engineering: bridges, dams, suspension cable bridges, concrete structure reinforced by steel and composite
- Aircraft and aerospace: aerospace structures, wings, fuselages, bulkheads, fuel tanks, rocket engines, turbine engines
- Maritime: ship hulls and superstructure, tanks, cranes and derricks, engine and power plants
- R&D: to monitor and study the damage in materials and their mechanical properties. R&D in the control of the damage in materials has grown in the last 20 years.
Rapallo is an experienced user of Acoustic Emissions testing to optimise the performance of our clients assets from LNG plant to tanks and smelters.
Acoustic Emissions (AE) Enquiries
To receive information on Rapallo Groups NDT & Condition Monitoring capabilities, or to make an enquiry about a project:
Contact: Dean van der Woude, Project Engineer