Heat Exchanger Systems, Inc.
Consulting Engineers & Nondestructive
Condenser Retubing Services
HES can provide a tube purchase specification for the condenser tubing.
HES can include any requirements desired in addition to those normally imposed by HES. Since HES has previously developed "in-house" tube purchase specifications for all commonly used tube materials, a tube purchase specification can be issued very quickly.
HES has extensive experience providing tube mill QA for condenser tubing, and therefore, has incorporated QA requirements in its purchase specifications resulting from previous tube mill inspection programs.
HES can develop a bid specification for selection of a retubing contractor. The HES specification includes criteria and required technical responses from the prospective bidders which will assist in identifying competent bidder's.
Since HES has previously prepared similar specifications, the HES "in-house" specification can be expeditiously modified to include all requirements particular to your retubing, as well as any additional requirements requested.
The HES Contractor retubing specification incorporates all of the criteria developed during the course of multiple field retubing QA assignments by HES Engineers.
Such criteria include cleanliness requirements, tooling, tooling changeout/replacement, instrumentation/measurement requirements, and material handling requirements.
HES can provide a finalized specification suitable for issue to prospective bidders.
Contractor Bid Evaluation
HES can assist with evaluation of the bids received from potential retubing contractors. HES places emphasis on the technical content of the bids received. HES considers proposed tooling, scheduling, man-loading, subcontractors, equipment operating parameters, and past contractor experience with similar projects. HES can make recommendations, rank the contractors, and provide a basis of selection.
During both the pre-outage and outage phases of a retubing project, a number of issues arise requiring engineering resolution. HES proposes to assist engineering personnel by providing input in the are of data analysis, historical background with similar problems, inspections/interviews at installations which may provide useful information, identification of potential resolutions, and making recommendations on optimal resolutions and their impact upon the retubing of the condenser. Specifically, the areas of assistance most frequently provided by HES include the following:
Tube Vibration Analysis
Tube Stake Design/Installation Plan
Modifications Resulting From Uplift Analysis
Performance Monitoring Instrumentation Improvements
Tubesheet Stress Analysis
Modifications Resulting From Tubesheet Stress Analysis
Tubesheet-to-Shell Joint Design Evaluation
The potential problem with tube vibration after retubing with titanium is of particular interest.
Contractor Procedure Review
HES can review all retubing contractor operating procedures for technical adequacy based upon extensive experience with similar condenser retubings. Having all operating procedures complete and technically correct with regard to tooling, sequence of work, and QC requirements will be key to completion of the retubing project in the time available, as well as providing assurance of condenser reliability.
The purpose of the fouling test is to determine how the tubes to be installed during the retubing will foul when placed into normal operation, and to select method(s) of water treatment or mechanical cleaning which will minimize water-side fouling and therefore maximize electrical generation.
The test proposed by HES includes the installation of test equipment in a slipstream of circulating water representing both condenser inlet and outlet circulating water temperatures. The circulating water will be passed through sections of tubing surrounded by electrical heaters which will simulate the in-service condenser heat loading. Resistance to heat transfer through the tube walls are automatically calculated from power input and temperature measurements. Change in heat transfer resistance over time can be related to cleanliness factor.
HES can review all contractor/subcontractor schedules to check for inclusion of all required activities, proper activity sequences, and adequate man-loading. HES will base its review upon previous experience with schedules of similar retubings.
Tube Joint Test Plan
HES has extensive experience with development of tube joint test programs, having developed and analyzed pull-out tests for Northeast Utilities, Portland General Electric, Consolidated Edison, Cleveland Electric Illuminating, Mississippi Power Company, Florida Power and Light, Detroit Edison and numerous other utilities.
The HES program typically consists of the following elements:
Tubesheet hole measurement
Tube wall thickness measurement
"As-rolled" tube I.D. measurement
Calculation of apparent wall reduction (AWR)
Breaking of joint with a "hydraulic ram" and recording breaking force
Measuring I.D. of tubesheet holes after tube removal to detect ligament distortion.
Groups of tubes are expanded at increasing torque values in order to correlate joint strength with AWR. Since HES has previously conducted joint testing of titanium tubes expanded into solid titanium tubesheet tubes expanded into titanium tubesheets, it is expected that the optimal range of AWR will be in the range of 6-8%, at an expanding torque of approximately 130 inch-lbs.
In any case, the HES pull-out test will identify the AWR and expansion torque yielding the greatest joint strength, without measurable ligament distortion.
HES can include testing of various types of "serrated" joints.
HES will develop a detailed joint test plan, including necessary materials and test equipment/instrumentation, as well as recommending companies to perform the actual testing.
Tube Mill Inspection
HES can provide shop QC coverage during the production of tubes.
Our inspections include review of shop and laboratory procedures, witnessing of all aspects of production and QC testing, verification of compliance with all procedures/special specification requirements and performance of cross check verifications of production tracer and reject records.
HES can provide necessary precision instrumentation to perform the cited verifications.
HES can prepare detailed inspection plans for condenser internals and waterbox inspection, as well as a separate contractor retubing operations inspection plan.
The condenser internals/waterbox inspection plan defines general procedures, types of measurements, and acceptance criteria for the inspections.
The retubing operations inspection plan defines similar criteria for tube cutting/removal, tubesheet removal/installation, new tube insertion, and tube-end expansion.
HES provides experienced personnel to assist with conducting the condenser internals/waterbox inspection.
Retubing Field QC
HES provides experienced personnel on-site during the actual retubing to assure that all requirements of the retubing operations inspection plan are being followed. Should HES discover any non-conformances, HES will advise of potential impacts and methods of resolution. For further information regarding Retubing Field QA: FieldQC
The HES coating consultant, George Spires, provides recommendations regarding bidders qualifications and past performance. He also provides order of preference recommendations concerning applicator/material selection. Prior to the start of work, the HES coatings consultant will review all work procedures and provide comments to NUSCO based on past experience.
During the field portion of the work, our coatings consultant can oversee all contractor operations to assume compliance with all specification and procedural requirements.
Condenser Tightness/Performance Testing
The HES tightness test plan includes the following tests:
Shell hydrostatic test for tube joints and tubesheet/shell joints.
Fluorescent dye test under "blacklight" for tube joints.
Waterside hydrostatic test for waterbox-to-tubesheet joints.
Helium leak test for all affected joints after unit start-up.
A valve line-up procedure has not been included in the scope of services but could be provided upon request.
The shell side of the condenser should first be filled with water slowly (no more than 1/2 inch/minute) so that leaking tube joints can be re-rolled. If the shell is filled too rapidly, it will not be possible to detect leaking tube locations. Once the water level has reached a level approximately 6 feet above the top of the tube bundles, the level should be maintained for a minimum of 12 hours, checking for leaks at all joint locations.
Fluorescent dye should then be mixed with the water on the shell- side and the tube joints examined very carefully for "weeping" joints.
The waterboxes should then be filled and pressurized to at least the shutoff head of the circulating water pumps, in order to check the waterbox-to-tubesheet joints and expansion joints for tightness.
Once the condenser is placed back in service, and the unit is at a minimum of 50% of full load, the tube joints and all other joints/penetrations should be helium leak tested to assure leak tightness.
HES can develop a test plan to establish the accuracy of modified/newly installed instrumentation. The test plan will include calibration techniques and comparison of data with past/expected operating parameters.
HES can also provide a plan to establish a set of "benchmark" condenser operating parameters for the retubed condenser against which future performance can be compared. The benchmark parameters include duty, temperature rise, inlet water temperature, subcooling, and dissolved oxygen.
For additional information regarding condenser retubing, contact Robert J. Bell at (781) 337-9400 or click here to email Bob.