Scope of Acoustic Emission Testing in the Underwater Domain Awareness (UDA) Framework
Muhsin Ahmad Khan
Offshore engineering project designs are often based on exaggerated underlying assumptions. This design approach helps engineers account for unpredictable environmental and operational extremities that may occur during the lifespan of such a project, making any failure during operation unacceptable. However, failure of offshore structures is not something unheard of before. Whenever one hears about a disaster at sea, one would usually imagine a sinking ship. But, disasters at sea are not just limited to damaged vessels. Recently, most of the reported offshore accidents have been associated with the failure of offshore engineering operations such as oil rig failures, pipeline explosions, crane failures, construction, etc. Some examples include the Deepwater Horizon spill, Piper Alpha spill, and the most recent natural gas pipeline disaster in the Gulf of Mexico. Such disasters have a severely detrimental impact on the biotic and abiotic components of the aquatic ecosystem, and therefore, need to be prevented at all costs.
Failure of offshore engineering projects is broadly classified into engineering and administrative-related causes. Engineering related causes are mainly associated with poor design or structural damages incurred during manufacturing, transportation and installation. However, it is crucial to understand that engineering and administrative causes usually go hand in hand. The Deepwater Horizon oil spill, which is regarded as the biggest oil spill in the history of offshore oil and gas disasters, was mainly caused due to poor engineering exploration and design. Investigations revealed that the concrete wall around the reservoir cores was damaged. The entire catastrophe could have been averted if the technical issues had been diagnosed earlier through routine checks or monitoring. Negligence of the operators (Transocean and Halliburton) and the owners (BP) are solely responsible for this disaster.
The UDA framework can guide commercial organizations engaged in the exploitation of natural resources in establishing sustainable goals that limit them from excessive exploitation.
It is therefore implicit that fundamental and investment goals of an organization will determine the overall well-being of the project. Profit centered goals will promote negligence of standardized practices (safety and conservation wise) during the design stages and operational life of a project, thereby posing severe threat to the surrounding marine environment. Such events have mandated the establishment of a regulatory framework that helps the participating organizations establish investment goals that commit their intentions to sustainable offshore architecture and preservation. The UDA framework, as proposed by the Maritime Research Center, Pune, extensively deals with the exploration of the underwater domain. Recently, government institutions involved in maritime operations have expressed the importance of a UDA framework. The UDA framework can guide commercial organizations engaged in the exploitation of natural resources in establishing sustainable goals that limit them from excessive exploitation. In addition, the UDA framework can help such institutions regulate their investments in offshore projects, ensuring sustainable investments which further prevent organizations from neglecting their duties to ecological preservation.
From an engineering point of view, many mitigation solutions have been proposed that guarantee failure prevention. These include standardized design calculations and complex software simulations. However, these methods are confined to the design stage of offshore projects and can only predict potential failure modes to a certain extent as it is impossible to determine the exact severity of extremities (environmental or operational) during the working life of any offshore project. Therefore, actual observations can only be made post-installation through in-situ testing and monitoring.
the Acoustic Emission Technique, can offer a solution to examine the structural response at macro and micro scales, enabling abnormal behavior detection.
Non-Destructive Testing (NDT), specifically the Acoustic Emission Technique, can offer a solution in this regard. By incorporating this technique, structural response can be examined at macro and micro scales, enabling abnormal behavior detection. Engineers can use data from in-situ dynamic analysis by Acoustic Emission Technique as references for future projects. In addition, site engineers will be able to detect any signs of imminent threats of failure, thus preventing ecological catastrophes.
Acoustic Emission technique is suitable for structural monitoring applications. Standardized testing procedures (as prescribed by various engineering codes) for analyzing structural response will suggest the use of Acoustic Emission technique as it allows testing over prolonged time durations. However, using Acoustic Emission technique as an in-situ monitoring system can be challenging. Offshore structures experience continuous vibrations and deflections due to the dynamic nature of ocean currents and winds. To mitigate the effect of these loading conditions, the structure deflects in a manner by which equilibrium is obtained. This deflection is associated with the formation of acoustic emissions.
The main issue is, therefore, distinguishing and detecting abnormal emissions from noise. There are several techniques that can be used to tackle this issue and make Acoustic Emission suitable for onboard monitoring applications. In recent times, AI has shown huge potential in engineering applications. Using AI and ML based software can enable the detection of obscure emissions from noise data. In addition, reverse analysis approach can be implemented using mathematical models such as Finite Element theories for identifying and triangulating sources of emission. It would be safe to say that there is huge potential for NDT on the onboard structural monitoring front.
The structural integrity of offshore structures is vital from a conservation point of view and can be achieved through dynamic in-situ testing through Acoustic Emission Testing. Understanding failure mechanisms in arduous marine environments in different regions for different projects along with elaborate investment planning for sustainable operation can help in formulating effective mitigation techniques. This form of planning and development structure if implemented for existing and future marine engineering projects will contribute significantly to the preservation and exploration aspect of the UDA framework.