The retubing of a steam surface condenser involves a number of procedures which must be performed according to a set of procedures based upon the latest proven practices.

The purpose of the HES field retubing QA program is to ensure compliance with approved procedures and to identify and help resolve any problems which may arise in the course of the retubing. HES's involvement with field retubing starts with review of contractor procedures, and covers all steps of the project through final hydrostatic/helium leak testing.

A brief description of each of the services normally provided to the utility by HES during a condenser field retubing is as follows:

Preparation of Documentation

HES prepares tubesheet maps identifying the location of "100th hole measurements". These maps are used throughout the retubing to locate tubesheet holes which may require loctite, sleeving, or plugging, and identify where apparent wall reduction (AWR) measurements were taken.

HES also prepares forms for recording tubesheet hole locations and dimensional data taken before and after tube expansion in order to assure that acceptable tube joint strengths are achieved via the AWR control technique.

Inspection of Tubesheets and Condenser Internals

After tube removal, HES personnel inspect tubesheet holes for defects. Inspection commences on the outlet tubesheets and is carried out so as not to interfere with tube removal activities. Each 100th hole is marked on the tubesheet with non-water soluble markers, as well as each defective tubesheet hole in a different non-water soluble color.

Holes ID's are also measured and recorded for assurance of proper tack tube location. HES reviews these tack tube locations prior to tube expansion to assure minimal tubesheet distortion.

HES inspects the condenser internals in order to determine any corrective action, e.g., support plate and/or baffle replacement or repair which must be undertaken prior to new tube insertion.

Tubesheet Hole Repair

HES determines what measures should be taken to repair tubesheet holes with surface scratches, gouges, cuts or excessive ovality. HES monitors repair procedure implementation to ensure repair acceptability.

Equipment & Operator Qualifications

HES personnel monitor the qualification of rolling motors, rolling motor operators and tube flaring personnel on sample tubesheets.

The following data is recorded for both equipment and operator qualification:

- remarks and/or comments

HES personnel confirm measurements listed on data sheets independently from the retubing contractor.

HES also provides input regarding test block rolling acceptability.

Tube Insertion and Rolling

HES personnel witness the transfer of tubes from the storage area to the retubing work area, tube handling from boxes to insertion, and tube insertion.

Once production rolling has commenced, HES records the rolling torque and collar setting of each rolling motor at the beginning and halfway through each shift, checks dynometer calibration periodically, and records 100th hole measurements and calculates AWR's after each 100th tube is rolled. If 100th hole AWR is out of range, HES ensures that the rolling motor is removed from service and adjusted prior to being placed back in service.

HES monitors retubing contractor activity to ensure that the proper number of expanders per rolling motor are being utilized, proper expander lubrication is supplied and used and that expanders are removed from service, and inspected at an acceptable frequency.

Waterbox Removal/Re-installation

HES personnel monitor the removal/re-installation of the waterboxes, tubesheet to waterbox gasket, installation, as well as proper bolting torque to assure leak tight joints.

Hydrostatic/Helium Leak Testing

HES personnel witness filling of the shell of the condenser to ensure that the rate of filling will allow detection of leaking tube/tubesheets joints. Once all leaking joints have been identified and rerolled, HES assists contractor/utility personnel with locating "weeping" tube/tubesheet joints utilizing fluorescent dye and a black light.

Once the unit is back in service, HES can provide Helium leak test procedures and assistance with finding air/water in-leakage locations.

Summary

In theory, the field retubing of a condenser is a relatively simple process of tube removal/reinsertion followed by tube expansion. In reality each step of the retubing process, if not performed properly, can result in tubesheet/tube damage, air/water in-leakage, or poor thermal performance.

HES Engineers are thoroughly familiar with condenser retubing QA, having been hired to perform field QC on numerous large power plant heat exchangers, both nuclear and fossil fueled.

HES would be happy to design a field retubing QA program for your condenser.

For information regarding HES Retubing Services please contact: