For years, the solution for pitted, cracked or corroded heat exchanger tubes has been to plug the defective tubes until either the tubes could be replaced or the heat exchanger itself was replaced. Both ultimate options are expensive and require large time and labor commitments.

Using its extensive knowledge of the nuclear power industry and steam generator technology, Framatome Technologies, Inc. (FTI) has perfected a patented heat exchanger sleeving process that has been used in numerous facilities to enhance plant efficiency while prolonging the life of aging heat exchangers. Damaged or plugged tubes can be returned to service using this process at substantially lower cost than replacement of either the tubes or the heat exchanger. Sleeve installation can be scheduled during routine maintenance outages to avoid impacting plant operation. This innovative sleeving technique can extend the life of heat exchangers in nuclear and fossil fuel power plants as well as refineries and chemical plants.

One of the most recent installations was completed for Baltimore Gas and Electric’s (BGE) Calvert Cliffs Nuclear Power Plant Unit 1. Of the six condenser waterboxes, C. Lee Friant, a Lead Engineer for BGE responsible for balance-of-plant heat exchanger NDE, noticed that one was 8.9% plugged (11A) and another 5.4% plugged (12A) due to seawater pitting inside the condenser tubes. Waterbox 11A’s cooling capacity was close to falling below nominal operating requirements and, although 12A was not yet critical, it was decided to repair it during the March 2000 scheduled maintenance outage. Based upon eddy current and video probe inspection data, BGE determined that sleeving the damaged and previously plugged tubes would regain a large percentage of the component’s heat transfer capability. BGE had used FTI for eddy current and tube plugging on steam generators and were familiar with the sleeving option. A bid invitation was issued and, according to Friant, “FTI was the best from both a cost and technical standpoint.”

The sleeve design and installation is customized to each plant’s requirements and specifications. A typical installation requires a minimum of three steps: feasibility study, design and testing in FTI’s lab, and installation. Once FTI was awarded the contract, additional analysis of the tube material and damage type, wall thickness, overall condition of the tubes, operating pressure and temperature conditions, space limitations within the waterbox, and the number of tubes affected was completed. Initial inspections revealed that the working space within the waterbox was limited. Sleeve lengths would be limited to 14” to 84” due to the space constraints. Since most of the damage was near the inlet ends of the tubes, both BGE and FTI felt that most tubes could be sleeved.

FTI designed and tested the sleeves for the BGE tubes. Sleeve installation tools specific to the Calvert Cliffs condenser tube size were constructed. Sleeves were installed and tested by FTI in spare condenser tubes, provided by BGE, using production tooling. By replicating the procedure in the lab prior to arriving on site, FTI ensured that the sleeving could be completed within the allowable time frame. Sleeve leak rates were tested under operating conditions. Also, an analysis of the sleeved-to-plugged tube ratio for pressure drop and heat transfer was completed.

Three days were allocated to FTI to install approximately 1000 sleeves. Once on site, plugs were removed from tubes to be sleeved and returned to service. The tubes were thoroughly inspected to ensure that additional damage had not occurred since plugging. After the sleeve was inserted, it was expanded to fit snugly against the inside of the tube over the majority of its length. Next, the near end of the sleeve was roll expanded into the tubesheet and the far end was roll expanded into the freespan end of the tube to provide the sleeve-to-tube joint.

Once the first eight 84” sleeves were installed, FTI conducted an eddy current inspection and a dimensional examination to ensure that the actual installation matched lab parameters. Based on the positive test results, production installation commenced. In the two waterboxes to be sleeved, 993 sleeves were installed at a rate of approximately 13 per hour. After installation of the sleeves in the 11A condenser, the percentage of tubes plugged dropped to 3.7% while 2.6% remained plugged in 12A. Final testing after startup of the units indicated improved flow rates and no leakage problems.

At the conclusion of the job, Friant commented that he was “very satisfied” with FTI’s work and in fact, BGE would probably do additional sleeving in 2002. Friant also noted, “They are very professional, their attention to detail is outstanding and they are easy to work with.”

click to Learn more of Framatome's Heat Exchanger Services