Advanced Fiber Optic and Ultrasonic Sensor Systems for Structural Health Monitoring of Pipes in Nuclear Waste Sites

Nuclear waste sites across the United States and other countries store, transfer and vitrify nuclear waste. These sites often require transfer pipelines for high and low level radioactive wastes in the form of solids/slurries, fluids including chemicals. Since, these pipelines deal with harmful nuclear wastes, structural health monitoring is of utmost importance. Pipelines are continuously monitored to enhance the safety of the people and environment around the facilities. Monitoring may involve leak, crack detection and wear (in the form of corrosion or thinning). Current research builds on author's previous work on sensors for erosion and thermal monitoring in pipes and plates [1, 2, and 3]. Present work involves a) validation and monitoring of a novel advanced Fiber Optic Sensor System to detect cracks and leaks in carbon steel pipes and b) the use of Ultrasonic (UT) sensors to detect thinning in pipe sections due to erosion-corrosion using small coupons. The fiber optic sensors developed by CEL [4], are used in conducting engineering scale testing on an in-house designed and assembled erosion pipe flow loop. The loop consists of 2 and 3 inch straight and elbow sections of carbon steel replicating the pipelines at the sites. Three fiber optic sensors are placed at critical locations around the loop. The equipment also includes a communication box and a laptop device for data acquisition. The sensor system uses a combination of fiber optic and acoustic technologies to accurately identify the location of a pipeline leak or crack. Sensors capture the changes in pressure caused by the fluid/slurry flowing through the loop. A “zone” is defined as the distance between any two sensor points. When any two sensors simultaneously detect a leak, a determination can be made as to how far from each sensor the activity is occurring and “zero in” on the event. A number of zones may be linked together to manage vast expanses of pipeline. Sensors provide instantaneous event data to the hardware (the interrogator), and the interrogator may be located great distances from the actual pipeline in secure, environmentally protected areas. Multiple Interrogators may be linked together that are simultaneously streaming real-time data to the command and control software. Event notifications may then be managed from the customer's control room, or immediately “pushed” to a variety of mobile devices to alert personnel of the situation [5]. Additionally, Ultrasonic (UT) sensors are used for thickness measurements in pipes. The objective is to measure the wear in pipelines due to erosion-corrosion using small scale erosion coupons. These erosion coupons are made of carbon steel with ½ inch in diameter and 1 inch height. The method involves insertion of the coupons into holes drilled in the pipe sections of the erosion loop. This process ensures that the coupons are in contact with the flow stream and hence eroded in a minute scale over a period of time. The coupons have a slot for insertion of the sensors to measure the thickness in real-time when needed. Upon successful testing of the coupon and sensors, the method can be used to predict the erosion rates and hence the remaining useful life of the pipe sections without having to replace them unnecessarily. Hence, the present research conducts structural health monitoring of carbon steel pipes using fiber optic and UT sensors. The sensors have been validated and verified for their potential future deployment in the nuclear waste sites.