HEAT EXCHANGER TUBE SIDE MAINTENANCE REPAIR vs. REPLACEMENT Bruce W Schafer Framatome ANP, Inc. 155 Mill Ridge Road Lynchburg, VA 24502 (434) 832-3360 bschafer@framatech.com 1 HEAT EXCHANGER TUBE SIDE MAINTENANCE REPAIR vs. Replacement Bruce W Schafer Framatome ANP, Inc. 155 Mill Ridge Road Lynchburg, VA 24502 (434) 832-3360 bschafer@framatech.com Abstract Thetraditionalmethodofrepairingdegradedtubesinshell-and-tubeheatexchangersisto removetheeffectedtubesfromservicebyplugging.Sinceheatexchangersaredesignedwith excess heat transfer capability, approximately 10% of tubes can be plugged before performance is affected.When the number of plugged tubes becomes excessive, heat exchanger efficiency is lost,resultinginreducedpoweroutput,highsystempressuredrop,furtherheatexchanger damage, or abnormal loads placed on other plant heat exchangers. As an option to component retubing or replacement, repair methods, including tube sleeving and tubeexpansion,haveproventobeaneffectivemethodtorepairdefectivetubesandkeepthe existingheatexchangerinservice.Forthesleevingprocess,anewtubesectionisinstalled inside the existing tube to bridge across the degraded area.Tube expansion is used to close off a gapbetweenthetubeandthetubesheetorendplate(toeliminatealeakpath)orbetweenthe tube and tube support (to minimize vibration).While not all heat exchangers can be returned to their original design condition by performing tube repairs, in some instances it may be possible togetmanymoreyearsofusefullifeoutofaheatexchangeratafractionthecostof replacement. This paper presents options which the Plant Maintenance Engineer should consider in making the repair versus replacement decision.This includes the repair options (sleeving and tube expansion), other conditions within the heat exchanger, and the effect of tube repair on heat exchanger performance. Introduction Traditionally, when maintenance is performed on shell-and-tube heat exchangers, the only options considered when tube defects are found are to plug tubes and, when the number of plugs became too great, replace the heat exchanger.The decision to replace the heat exchanger was based on a number of factors.These included: the number of tubes plugged, the number of forced outages due to tube damage (and the cost associated with replacing lost power and repairing the damaged tubes), the impact that the plugged heat exchanger is having on the plant (due to lost flow or heat transfer surface area), the rate at which tube plugging is occurring, the availability of funds to replace the heat exchanger, and the expected life of the unit (how much longer will the unit operate before retirement). 2 From a sampling of industry data, tube failures have been shown to cause between 31% to 87%(depending on the data source) of the events related to feedwater heaters (1).Since so many of the failures were related to the tubing, the replacement of an entire heat exchanger due to damage in one area is an expensive as well as a schedule and manpower intensive option. The typical means for major heat exchanger repair included complete replacement, rebundling, and retubing, as described below. For the replacement option, the entire heat exchanger shell and tube bundle are replaced with a new unit. For rebundling, the shell is temporarily removed from the heat exchanger and the old tube bundle, including, at a minimum, tubes, tube supports, and tubesheet, are removed.A new tube bundle is inserted and the shell is welded back in place. For retubing, either the shell (u-tube design) or tube side access cover (straight tubes) is removed from the heat exchanger and the old tubes are removed from the bundle.New tubes are then inserted and re-attached to the tubesheet (typically by either mechanical expansion, welding, or both).In many instances, the existing shell side hardware is used as-is, although some modifications may be made.Retubing is typically performed on straight tube heat exchangers, such as condensers and coolers. Since the 1970s, tube sleeving has been used to allow damaged tubes to remain in service.The sleeves are installed by various means (roll, explosive, or hydraulic expansion, explosively welded, or press-fit or epoxied in place) over the defective area of the tube.Through the use of sleeving, which is a low-cost option to retubing, rebundling, or replacement, the useful life of a heat exchanger can be economically extended.The decision to perform sleeving also can be made with short notice as opposed to replacement (2-6 weeks compared with 18 months), possibly allowing repairs to be performed the same outage that the damage is noted. Tube expansion also can be performed to minimize or eliminate leakage within heat exchangers.In the tubesheet, tubes can be re-expanded to strengthen the original tube-to-tubesheet joint, reducing or eliminating leakage and prolonging the life of the heat exchanger.Expansions also can be made deep within the tube to expand the tube into tube support plates and end plates.These expansion can reduce tube-to-plate clearance for vibration control or, at end plates, to minimize steam flow from the high to low pressure side of the plate. Repair vs. Replace Factors To Consider There are numerous factors to consider when deciding whether to repair the tubes in a heat exchanger or to perform a larger repair scope and rebundle or replace the component.The following factors should be considered when making the repair vs. replace decision. The budget available for repair or replacement needs to be determined.Typically, the cost of performing a substantial heat exchanger repair (consisting of plug removal, tube inspection, tube expansion, and sleeving) is less than 10% of the cost of replacing the unit.Because of the lower cost, the payback time on the repair option is much shorter than for replacement. If the heat exchanger is critical to plant operation (either from a safety, efficiency, or power production standpoint) or is resulting in costly forced outages, it may be possible to justify a 3 repair to the unit in the near-term and a scheduled replacement when a longer outage can be planned. If there are a large number of tube plugs to remove, or if they are difficult to remove (explosive or welded), then the cost to repair the heat exchanger will increase, and the scheduled time needed on-site may not fit within the outage window.If it appears that tube repair may be possible, it may be worthwhile to plug tubes, using removable plugs, until a certain quantity of tubes are removed from service.At that point the plugs would be removed and sleeves installed, thereby minimizing the overall maintenance cost. The location and quantity of the tube defects need to be examined to decide if tube repair is an option.Tube repair may be appropriate if the damage is limited to a certain area of the tube, which would allow the use of a short repair sleeve.If the damage is over a significant portion of the tube, it is possible to install a longer sleeve (up to the full length of the tube) to ensure that all tube defects are repaired.However, if the u-bend region of the tube is damaged then tube repair is not possible.Also, it would not be possible to install a sleeve if a large portion of the tube had damage but there was inadequate clearance for a long sleeve at the tube end. One of the more important items to consider when deciding whether a heat exchanger can be repaired is the condition of the remainder of the heat exchanger.The condition of the shell side components, such as the impingement plates, tube supports, end plates, and other structural members, should be in good shape if a long term repair is being planned.An evaluation also should be made of the shell thickness in areas that are prone to shell erosion/corrosion.If the tube repair is only a short-term fix, to allow component operation until a replacement heat exchanger can be installed, the condition of the shell side is not as critical. The life expectancy of the power plant needs to be factored into the decision to repair or replace a heat exchanger.If the only problem with the heat exchanger is in one section of the tube, and the expected run time on the unit is relatively short, it would be advantageous to repair rather than replace the heat exchanger since it will be very difficult to pay back the cost for replacement over the remaining plant life. The outage time required to repair a heat exchanger, even when tube and shell side inspections are performed, is typically much less than for replacement.In addition, very few, if any, plant modifications need to be made to make the repairs.This allows other work to be performed in the vicinity of the heat exchanger. Along with the shorter outage duration, the site support required for repair is much less.Usually, there are no shell or head modifications required since all work can usually be performed through the manways and pass partition plates.Less repair equipment is required, resulting in less space being needed in the area of the heat exchanger for setup and storage. In addition, the time required to prepare for tube repair is much less than for replacement (2-6 weeks compared with 18 months), allowing a decision on repair to be made just before, or even during, an outage. At nuclear plants, the added cost for the disposal of radioactively contaminated heat exchangers must be taken into account.Before disposal, there is the cost of surveying the 4 heat exchangers for release and, if contamination is found, they must either be decontaminated or disposed of as radioactive waste.Tube repairs can eliminate these costs. If the heat exchanger is being replaced to eliminate detrimental materials in the cooling system (i.e. copper in the condensate/feedwater system) then tube sleeving will not be beneficial.The only practical solution would be to retube/rebundle/replace to change out the tube material. Heat Exchanger Repair Options There have always been options available to either repair or replace heat exchanger tubes in the event that tube leakage or degradation is present.The initial option, after the problem tubes have been located (either through non-destructive examinations, such as eddy current testing, visual inspections, or leak tests) is to plug the tube.Depending on the type of service and operating pressures of the heat exchanger, various types of plugs are employed.These include tapered fiber and metal pin plugs, rubber compression plugs, two piece ring and pin plugs, two piece serrated ring and pin plugs (installed with a hydraulic cylinder), welded plugs, and explosively welded plugs.In addition to the tube end plug, there also may be a stabilizer rod or cable that is inserted into the tube to minimize future tube vibration damage. At the beginning of the life of a heat exchanger, inserting a few plugs into damaged tubes has little effect on the performance of the heat exchanger.However, if heat exchanger problems continue, and the number of plugs increases significantly, it is possible that the heat exchanger will eventually reach a point that it will not handle the full load that is placed on it.This is due to a combination of loss of heat transfer area and the increased pressure drop.In addition, as the number of plugged tubes increases, abnormal temperature conditions (either hot or cold spots) may be set up in the heat exchanger.These conditions can result in an acceleration of tube damage, creating a faster demise of the heat exchanger. Once the number of plugs reaches a unacceptable level, the heat exchanger will need to be repaired, replaced, or bypassed.However, bypassing the unit is usually not recommended, at least for a long time period, since it will result in a loss of efficiency and heat transfer area.Also, the heat load from the bypassed heat exchanger will be transferred to another heat exchanger in the string, resulting in greater than normal operating flow rates and higher degradation in that heater. The following sections show the options that can be used to replace or repair the entire heat exchanger or just the tubes. Retubing If the unit has straight tubes, good access, and the remaining components (shell, tube supports, internal structural pieces) of the heat exchanger are in good shape, the tubes can be replaced.The old tubes are removed from the unit and new ones, typically manufactured from an improved material, are inserted, and then expanded, into place.Insertion of the new tubes is shown in Figure 1.In addition to performing retubing to replace damaged tubes, retubing has been performed to eliminate detrimental materials (such as copper from condenser tubes) to 5 minimize damage to other equipment within the plant (nuclear steam generators or fossil boilers). Figure 1 Condenser Retubing Rebundling Some heat exchangers are designed to be rebundled rather than replaced.For these units the entire tube bundle, including tubes, tubesheet, and tube supports are replaced, as shown in Figure 2.The original shell and any other internal structural pieces would be reused (although any necessary internal repairs could be made when the shell was removed).The new tube bundle can be manufactured to ensure that original design problems with the existing unit are corrected.However, the same basic design must be maintained since the new bundle must fit within the existing heat exchanger shell.Rebundling costs about 15-25% more than retubing (1). Figure 2 Heat Exchanger Rebundling 6 Replacement A third and typically widely used option is to replace the entire heat exchanger, as shown in Figure 3.Full replacement allows alternate tube materials, changes in heat transfer area, and structural changes to be employed, including added clearances in areas where erosion or other problems may be occurring, to ensure that the current heat exchanger problems do not re-occur in the future.However, the cost associated with a full replacement is the greatest of the three options, about 5% more than for rebundling (1).In addition, there are no guarantees that the new heat exchanger design will not have new, unanticipated problems. Figure 3 Heat Exchanger Replacement Sleeving An alternate approach to retubing, rebundling, or replacement of a heat exchanger is to install sleeves over the defective portions of the tubes The sleeve consists of a smaller diameter piece of tubing that is inserted into the parent tube and positioned over the tube defects.After insertion, each end of the sleeve is expanded into the parent tube material.These expansions serve the dual function of structurally anchoring the sleeve into the tube and providing a leak limiting path, allowing the sleeve to become the new pressure boundary for the tube.This means that a sleeved tube can have a 100% through-wall indication and still remain in-service, since the sleeve is now the new structural and pressure boundary.The installation of the sleeve into the tube will allow the majority of the tubes heat transfer area and flow to be maintained. If heat exchanger repair by sleeving is a possibility then a strategy needs to be used to prepare for future repair.It may be cost effective to plug a quantity of tubes, per the non-destructive examination results, each outage using a removable plug.When the quantity of plugged tubes reaches a certain level the plugs can be removed and sleeves installed.Using this approach will minimize the cost and time during each inspection outage while allowing the maximum tube repair later in the heat exchangers life. 7 There are three types of sleeves that are installed into heat exchanger tubes.These are full length, partial length structural, and partial length barrier sleeves.The three types are discussed below.Figure 4 shows the sleeve layout. Figure 4 Heat Exchanger Sleeve Designs Full Length Sleeve These sleeves are installed from one end of the tube to the other in straight tubed heat exchangers.After insertion, the full length of the sleeve is expanded into the parent tube.This step serves the dual purpose of maintaining heat transfer as high as possible (typically 75%-90%) while minimizing flow pressure drop through the tube.After the full length expansion step, shown in Figure 5, the sleeve ends are trimmed flush with the existing tube ends and the sleeve is roll expanded into the tubesheet. The full length sleeve is typically used in a condenser or cooling water heat exchanger when the tubes have multiple defects along their length.Full length sleeving is an attractive option when a relatively small percentage of the tubes require repair.Through sleeving, the majority of the tube heat transfer area can be left in service, resulting in a heat exchanger that is close to its as-designed condition. Full length sleeving is comparable in many ways to retubing in the methods employed to install the sleeves.However, since removal of the existing tube is not required, and the typical number of tubes that will be full length sleeved are below the number that would be retubed, the cost for 8 material and manhours are much less than for retubing, making sleeving a cost-effective option to return and keep tubes in service. Figure 5 Full Length Sleeve Expansion Partial Length Structural Sleeve This type of sleeve is used to repair shorter defects in the tube.The sleeve can be installed anywhere along the straight length of the tube.Various methods are used to expand the sleeve in place.These include roll expansion (both in the tubesheet and in the freespan portion of the tube), hydraulic expansion in the freespan portion of the tube, and full length expansion.These expansion types are discussed below.The installation of a hydraulically expanded sleeve is shown in Figure 6. If one end of the sleeve is in the tubesheet, a torque-controlled roll expansion will be made.This expansion is similar to the original tube-to-tubesheet roll.Freespan roll expansions are made to either a torque controlled setting or to a diameter controlled hardstop setting.Usually, freespan roll expansions are only used when the sleeve length is relatively short, since it can be difficult to insert a roll expander deep into the tube.Both the tubesheet and freespan roll expansion parameters are set so that they can provide both the structural and leakage requirements for the sleeve. For sleeves installed deep within the tube, a hydraulic expansion device is used to connect the sleeve to the tube.The expander consists of multiple plastic bladders that are filled with high pressure water.As the water pressure increases, the bladders expanded against the inside of the sleeve, pushing the sleeve into the tube.The expansion process, which is computer controlled, continues until either a preset volume of water or a preset pressure is reached.At this point the sleeve is properly expanded and the bladders are depressurized.Hydraulic expansions can be made anywhere along the tube length since the expander is connected to flexible high pressure tubing and is not restricted by tube end access.The 9 expansion parameters are qualified to meet the proper structural and leakage requirements for the sleeve. Full length expansions are not usually used for structural or leak limiting purposes but instead are used to improve heat transfer and flow through the sleeve and to close the annulus between the sleeve and tube.The full length expansion is made by placing a tool, with seals on each end, into the sleeve.The inside of the sleeve is filled and then pressurized with water to a preset pressure setting, expanding the sleeve into tight contact with the tube.After the full length expansion is made, the ends of the sleeve are typically either roll or hydraulically expanded to form the structural and leak limiting sleeve-to-tube joint. Many times, the partial length structural sleeves are used to repair indications at one particular area of the tube, such as wear damage at tube support locations, cracking in roll transitions, or pitting indications at one discreet location along the tube length.Longer versions of these sleeves also have been used to repair an entire damaged section of a heat exchanger, such as a desuperheater or drain cooler section of a feedwater heater.Because of the wide variety of uses, the sleeve length can range from as short as 1 foot to over 12 feet in length. Qualification testing is performed on the structural sleeves to ensure that they can withstand the design temperature and pressure conditions imposed on them.The test results must show that the sleeve will be the new pressure boundary even with a 100% through-wall indication in the parent tube.Sleeves of this type, using mechanical expansions (roll and hydraulic), have reliably been in-service for more than 15 years. Figure 6 Partial Length Hydraulically Expanded Structural Sleeve Installation Partial Length Barrier Sleeve These sleeves, also known as shields, are used at the ends of the tubes to act as a barrier to tube end erosion.These sleeves are usually very thing, are not designed to act as a pressure boundary or structural repair, and are installed in areas of high turbulence.The materials for these sleeves are compatible with the existing tube material and may include plastic inserts.The sleeves are 10 either roll or hydraulic expanded or pressed or epoxied in place.If tube end erosion is occurring, or is expected to occur, the use of these tube end sleeves will protect and prolong the life of the parent tube, although over time tube erosion may begin to occur at the end of the sleeve.Many heat exchanger tube ends have been protected with shields, significantly prolonging the life of the tubes. Items to Consider for Tube Repair Prior to choosing to perform tube sleeving, the following factors should be considered. The length, location, and quantity of tube defects that would require sleeving need to be determined.If the defects are in one or a few short areas then either a single or a couple of partial length sleeves could be used.However, if the defects are spaced throughout the length of the tube, then the only option would be a full length sleeve. The parent tube in the area where the sleeve will be expanded is to be defect free.This will insure the highest sleeve-to-tube joint integrity.Also, the tube support designations must be clearly identified to insure that the sleeve is installed at the correct location along the tube length.This is especially true in areas where there may be skipped baffles and the tube only touches every other support plate. The condition of the remainder of the tube away from the sleevable defects needs to be known.If there are u-bend defects that may require plugging then the tube should not be sleeved.Sleeving is an option if the remainder of the tube is in good shape. The space available at the tube end to insert a sleeve and its installation tooling needs to be known, as shown in Figure 7.If a short, partial length sleeve is being used, the amount of space required is not as critical, although there can still be access issues around the tubesheet periphery for hemi-head channel covers and at pass partition plates.However, if a full length sleeve is required, there will need to be a significant amount of clearance from the tubesheet face. Figure 7 Required Clearance for Sleeve Installation Inspection records need to be reviewed to determine if there are any tube inside diameter (ID) restrictions that would block the sleeve from being inserted to the target location.The size of the eddy current probe used for the inspection, plus any other hardware that has been inserted into the tube, can be used to help determine the tube ID access issues. 11 The post-sleeving tube inspection requirements need to be considered.Typically, the ability to inspect the tube beyond a sleeve is not a significant issue.While the presence of the sleeve reduces the inside diameter of the tube, which will result in the need for a smaller inspection probe, the probe will remain large enough to detect pluggable tube indications (usually greater than 40%), however small indications may go undetected. As part of the post-sleeve inspection, the sleeve and its attachment to the tube should be examined.There is no need to inspect the section of the parent tube between the sleeve expansions since this is no longer part of the pressure boundary. If tube cleaning is to be performed in the heat exchanger, then the type of sleeve to be installed needs to be evaluated.If on-line cleaning is performed, the sleeve size cannot restrict the passage of the balls or brushes.For off-line cleaning, the projectiles need to pass through the sleeve without becoming stuck.Many sleeves that are installed in tubes that require cleaning are full length expanded to ensure the best results for the cleaning equipment. If it appears that tube sleeving is possible, then information will be needed to ensure that the heat exchanger is properly repaired.The following information is used when planning for sleeving. Tube sleeving will need to be coordinated with eddy current inspection and plug removal. If it is expected that sleeving may be performed, then it is important that the proper sleeve material be purchased in advance of the job. The sleeve material needs to be compatible with the heat exchanger parent tubing and with the water chemistry within the heat exchanger.The galvanic corrosion potential between the sleeve and tube needs to be determined.Also, effects of crevice corrosion between the sleeve and tube, in the heat exchanger water chemistry, need to be considered to determine if sleeving is a viable repair option. The sleeve dimensions need to fit the heat exchanger operating and design conditions plus any restrictions within the tube ID.The sleeve outside diameter (OD) is to be designed to fit into the tube but must be long enough to limit the amount of sleeve expansion.The sleeve wall thickness needs to be sized for the heat exchanger operating parameters, including any ASME Code minimum wall thickness calculations, if needed.The sleeve length must be long enough to span the expected tube defects but needs to be sized to fit any tube end clearance restrictions. Before installing sleeves into heat exchanger tubes, testing needs to be performed to set the installation parameters.Depending on the type of sleeve being used, these tests may include setting the rolling torque, hydraulic expansion constants, and full length expansion pressure.In addition, depending on the application for the sleeve, there may be a need to do qualification testing, which would consist of hydrostatic leak and pressure tests and temperature and pressure cycling.These tests would verify that the expansion parameters were set correctly for the sleeve application. If a large quantity of sleeves are being installed, it may be necessary to calculate the heat transfer and flow loss due to sleeving.These calculations will give a sleeve-to-plug ratio that can be used to determine the expected improvement in heat exchanger performance after sleeving is complete (and tubes have been returned to service, if applicable). 12 The sleeve may need to be full-length expanded based on the heat exchanger operating environment.However, the production rates for sleeve installation are lower when full length expansions are performed.While full length expansion is typically not needed in many applications, such as most feedwater heaters, it should be considered for the following. if tube ID cleaning needs to routinely be performed if a long sleeve is being inserted that would severely restrict the tubes heat transfer or flow if the tube-to-sleeve crevice needs to be eliminated in a hostile water chemistry environment if there are large eddy current probe fill factor restrictions Heat Exchanger Tube Expansion Repair In addition to sleeving, it is possible to expand the tube to improve the heat exchanger performance.These tube repairs can minimize further tube damage and maximize the useful life of the heat exchanger.Two methods of tube expansion can be performed.One is to expand deep within the tube to close off a leak path between the tube and the end plate.The other is to re-expand the tube into the tubesheet to minimize tube-to-shell side leakage. Tube-to-End Plate Expansion In some heat exchangers, typically feedwater heaters, there are internal plates which separate one zone of the heat exchanger from another (usually condensing [steam] from drain cooler [liquid]).Due to the pressure differential across the plate, and the different temperatures and phases between the two sections, it is important that leakage not occur through the plate.However, in some feedwater heaters, the plate design is too thin, resulting in leakage of steam from the condensing to the drain cooler zones, as shown in Figure 8.When this occurs there is erosion of the end plate and tube vibration due to the high steam velocities and the steam condensing to liquid in the drain cooler region.The vibration causes wear at the tube supports which can lead to tube failure.The leakage of steam also increases the drain cooler temperature, resulting in a less efficient heat exchanger. 13 Figure 8 End Plate Leakage in a Feedwater Heater Expanding the tube can reduce the gap between the tube and the end plate.The expansion can be performed using either a roll or hydraulic expander.Once the expander is in position the tube is expanded until it contacts the end plate.An accurate expansion, which does not over-expand the tube into the plate (the tube needs to be able to slide in the plate after expansion so that it does not buckle during heatup/cooldown), needs to be performed.This can be achieved by using a computer controlled hydraulic expansion that automatically shuts off the pressurization system when it detects that the tube has contacted the plate. After the tubes are expanded into the end plate, the steam flow is minimized or eliminated, reducing the drain cooler temperatures and increases plant efficiency.Further tube damage, in the form of tube wear and adjacent tubes impacting on one another, will be reduced to nearly zero and the vibration operating stresses will be reduced significantly.The life of the heat exchanger will be increased at a minimal cost as compared with replacement. Tube-to-Tubesheet Expansion In some heat exchanger designs, with a certain combination of materials, leaks develop between the tube and tubesheet.In many low pressure units, the tube is only expanded into the tubesheet, with no subsequent weld.Many of the leaks that occur in these units are the result of a fabrication error and can be corrected by re-expanding the joint to the correct expansion size.However, leakage occasionally occurs in high pressure heat exchangers, typically feedwater heaters, even when the tubes have been welded to the tubesheet.The two prime causes of this leakage are in areas where the original tube-to-tubesheet weld has either cracked or eroded due to flow (in the case of soft materials, such as carbon steel) or where there is a crack in a tube-to-tubesheet expansion transition. 14 For the first case it may be possible to re-expand the tube using a qualified roll expansion process.The expansion would increase the contact pressure between the tube and tubesheet, increasing the resistance to flow and decreasing or eliminating leakage.This process could be performed on existing leaking tubes or preventatively on all tubes in the tubesheet. If cracking is occurring at the original tube expansion transition it may be possible to re-expand the tube deeper in the tubesheet (unless the cracking is occurring very close to the shell side of the tubesheet).The tube would be expanded using a qualified roll expansion process, to place the tube into tight contact with the tubesheet.This expansion would increase the contact pressure between the tube and tubesheet, increasing the resistance to flow and decreasing or eliminating leakage.This process could be performed either on existing leaking tubes or preventatively on all tubes in the tubesheet. Re-expanding tubes that either may be leaking or that could develop leaks in the future could significantly extend the life of an otherwise good heat exchanger.By re-expanding the tubes, forced outages can be avoided and damage from the high pressure water spraying on adjacent tubes and on the shell will be eliminated.The cost to perform tube re-expansions will be minimal when compared with the cost of replacement heat exchangers and the cost of forced outages. Items to Consider for Tube Expansion Repair The following factors should be considered to determine if tube expansion is possible. The portion of the tube to be expanded needs to be determined. If leakage is occurring through the end plate, the expander will need to be long enough to reach the end plate location.The tube should be expanded using a process, such as hydraulic expansion, that will not lock the tube into the end plate.This expansion will not only reduce leakage through the plate but also will minimize future tube vibration due to the tight fit between the tube and plate. If leakage is occurring within the tubesheet, due to either weld or tube cracking, a re-expansion process may be used.This process, typically a roll expansion, will re-expand the tube into the tubesheet to limit or eliminate leakage from the tube to the shell side of the heat exchanger. The condition of the remainder of the tube needs to be known.If there are cracks along the entire tube length then re-expanding the tube alone will not result in an improvement in heat exchanger performance. The space available at the tube end to insert the expansion tooling needs to be known.Usually either a roll or hydraulic expander will be used for this process.Unless a roll expansion is being performed at the end plate, the usual repair tooling is relatively short, although there can still be access issues around the tubesheet periphery for hemi-head channel covers and at pass partition plates. For tube end plate expansions, the eddy current inspection records need to be reviewed to determine if there are any tube inside diameter restrictions that would block the expander from being inserted to the end plate location.The size of the eddy current probe used for the inspection, plus any other hardware that has been inserted into the tube, can be used to help determine the tube ID access issues.The potential for any tube end restrictions, that might 15 limit tooling insertion into the tube, also need to be known so that tooling can be prepared to eliminate the restriction. If it appears that tube expansion is possible, then information will be needed to ensure that the heat exchanger is properly repaired.The following information is used when planning for tube expansion. Tube expansion will need to be coordinated with eddy current inspection and plug removal. The tube expander design (diameter and length) needs to be based on the requirements for the expansion.Before performing tube expansions into heat exchanger tubes, testing needs to be performed to set the tooling operating parameters.Depending on the type of expansion, these tests may include setting the rolling torque for tubesheet re-expansions or setting the hydraulic expansion constants for end plate expansions.In addition, for the tube-into-tubesheet re-expansion process, qualification testing should be performed.This would consist of hydrostatic leak and pressure tests and temperature and pressure cycling.These tests would verify that the expansion parameters were set correctly for the tube re-expansions. Conclusions The costs associated with heat exchanger replacement can be significant. These costs include the new heat exchanger or tube bundle, the manpower required to remove the old and install the new heat exchanger components, plant modifications to allow for the removal of the heat exchanger, and the amount of outage time associated with replacement.In addition, the replacement of a heat exchanger can adversely affect other work going on in the their vicinity.Because of the cost and time involved, and if the damage is confined to only the tubing (which is typically the case), repair of the heat exchanger, through either sleeving or tube expansion, should be considered.If the tube damage is confined to one general area, there is a good possibility that the expense of a replacement can be avoided.In addition, the time required to prepare for tube repair is much less than for replacement (2-6 weeks compared with 18 months), allowing a decision on repair to be made just before, or even into, an outage. By removing plugs and installing sleeves, it is possible to return lost heat transfer area to service.Tubes that would be likely to fail in the near term also can be repaired.This will improve the performance and reliability of the heat exchanger.The cost to perform the repairs is also much less than for replacement (usually less than 1/10th the cost).Sleeving has been shown to be a proven tube repair technique, having been performed since the 1970s.During this time, tube repairs have economically extended the useful life of heat exchangers worldwide. As the number of plugged tubes approaches the upper limits or if damage is consistently occurring in one area of a heat exchanger, tube repair, through both sleeving and tube expansions, should be considered to minimize future damage and extend the life of the heat exchanger. The following table shows the various heat exchanger repair options and the factors to be considered when choosing each of the options.Note that the table contains selected criteria for evaluating component repair versus replacement options.A final decision to implement a 16 particular option should be made on a case by case basis with proper weight given to all factors.The information listed in this table is for relative comparison purposes only. Table 1 Repair/Replacement Summary Table Repair Option Application On-Site Timeto Implement Lead Time Required to Implement Longevity of Selected Option Component Plus On-Site Cost TubePlugging All tube defects, but limited to ~10% of tubes before affecting performance Minimal time, typically