The project aimed to develop NDT methods of detecting chloride induced stress corrosion cracks, as well as the build-up of fouling deposits on the inside of process piping used in food production. Both aims were addressed using the same technology: Long range ultrasonic testing (LRUT). This relatively new technology has been investigated over the last decade primarily in the oil and gas industry, where it is used to screen long lengths of pipeline (up to 300m from a single test location) for gross corrosion damage.
The challenge in transferring this technology to the food and drink production industry is to design a system capable of withstanding the harsh environment within a heat exchanger - sensors will reside in relatively high temperatures and be immersed in steam.
As such, a sensor encapsulation method has been developed to protect sensors and cabling, which can be mounted within the steam chamber of a slightly modified pipe-in-pipe heat exchanger. These sensors periodically send a pulse of ultrasound through the metal of the product-carrying pipe, which is affected by any physical features and properties of the pipe itself.
Cracks will cause some of the ultrasound to be reflected back to the signal, whereas fouling deposits will attenuate the onward travelling signal. Both types of response can be recorded by the same sensors and digitally transmitted to a central control PC where it is stored and analysed. Analysis of the data allows an estimation of the level of fouling which is intuitively displayed in a traffic light system to clearly indicate when a particular pipe requires cleaning.
This can also be used during the cleaning process to determine the required cleaning duration and stop the process once the pipe is clean. In addition, if cracks are present a different signature signal will be received and an alarm can be displayed accordingly.
Detecting defects which are both invisible to the eye and located within process equipment is clearly desirable, but the most useful benefits of the project are to streamline the cleaning process.
Currently, process pipes are cleaned according to a prudent schedule, for a conservative duration. Fouled pipes reduce thermal efficiency and can lead to burnt deposits breaking off and entering the product, so manufacturers are keen to keep pipes clean, but conservatism is financially and environmentally expensive in terms of down time, cleaning products, and the clean water used for flushing.
This enhancement to the cleaning process offers 'triple bottom line' advances, as ensuring clean and hygienic production of food also presents social benefits, improving food quality and safety. www.lrutfood.co.uk.