Effective Expansion and Repair of Tube-to-Tubesheet Joints in a High Pressure Feedwater Heater

This paper demonstrates the extensive detail in initial testing, specification preparation, and final in-plant repair of seal welded and hydraulic expanded tube-to-tubesheet joints. The feedwater heater in question included T22 tube material and was installed new in 2002. With a little over 6 years of service, SaskPower realized that the tube-to-tubesheet joints on the PR1 (Poplar River Unit 1) number six high pressure feedwater heater had a significant number of leaks. After considerable investigation, 87 tube-to-tubesheet joint leaks were identified. No tubes were plugged based on actual tube failures. Rather than perform continued plugging of leaking joints, several repair strategies were developed. After a detailed review of the options, the repair procedure selected included repair to the tube-to-tubesheet joint seal welds that were leaking, followed by a full strength re-expansion of a 100% of the tubes. The initial recommended repair procedure was not deemed appropriate due to physical constraints. SaskPower worked closely and contracted with American Exchanger Services to complete a full strength explosive re-expansion of the tube-to-tubesheet joints, seal weld repair any remaining leaking joints as needed, and perform NDE necessary to assure tight tube joints. This paper will define the details of the initial investigation into the extent of the leaking, the development of the testing sequence and methods, and finally the preparations and repair strategy to bring this heater back to full operating status with minimal expense.