Improved permanently installed ultrasonic monitoring of structures at elevated temperatures

The objective of this proposal is to explore the feasibility of permanently installed ultrasonic monitoring of degradation mechanisms at elevated temperatures, with a special focus on hydrogen attack. To date, very few permanently installed monitoring systems exist. This is historically due to the lack of robust transducers that can survive harsh environments and the unavailability of cheap electronics and wireless communication that make manual intervention and its associated errors less important. As electronics and wireless technology have rapidly advanced, their mass deployment has become economically feasible. It is the ultrasonic monitoring technique and sensors that require research input in order to allow the development and future deployment of permanently installed sensors for monitoring material degradation. The author has recently developed a robust method that can be used to send and receive ultrasonic signals to and from test pieces at elevated temperatures for long periods of time. It is the aim to use this transduction method to couple ultrasonic signals into a test piece and monitor its degradation. From the many degradation processes that exist, hydrogen attack presents a problem in industrial applications at elevated temperatures and has been chosen as an example mechanism to focus on. The main challenge of the proposed work is to make the measurement system stable enough in order to reliably detect and monitor the relatively small changes that are introduced by a material degradation mechanism such as hydrogen attack (the ultrasonic velocity, attenuation and backscatter are changed by the formation of voids in the steel). The final aim is to experimentally demonstrate the feasibility of ultrasonic monitoring of hydrogen attack.

As expressed in their letter of support, BP are keen on monitoring hydrogen attack in their plants. The proposed monitoring approach could deliver valuable information about the plant condition while it is running and without costly disturbance of insulation materials. Thus the operation of plants will become safer and more cost effective. Although it is of interest to industry, it would be difficult to acquire industrial funding for this project as the outcomes are uncertain and far from current practice. As such the project is suited to funding by EPSRC in order to acquire enough knowledge and data to prove the feasibility of this approach. There are other damage mechanisms such as creep, stress corrosion cracking and inter-granular attack that present similar small changes in ultrasonic signal. The results from the proposed study may open up the possibility to monitor these other damage mechanisms which are more common concerns in the nuclear industry. Sparse ultrasonic data on specimens from hydrogen attack exists. Most analysis can be found in metallographic studies rather than ultrasonic studies. The outcomes would yield valuable data that could be used by other researchers interested in the effects of hydrogen attack on ultrasound or the effect of micro voids on ultrasound. Furthermore, it will enable the author to establish a strong track record in the field of ultrasonic permanently installed monitoring systems, which is a growing field driven by changes in technological capabilities and the necessity to reduce the relatively high frequency of errors introduced by manual operations.