ROLLING PROCEDURES

February 11, 2008

You are involved with a major retubing of a main condenser or heat exchanger.   You have spent a ton of money as compared to a few years ago.  In the past four years, the cost of copper is increased by a factor of 4 and stainless steel by a factor of 2.  The final  step in the procedure is tube end expansion.

As a responsible plant staff member, you realize that improper rolling of the tube ends could negate the effort and money already spent.  How do you insure that it is done correctly?

First, there are calculations to determine the proper amount of force used for tube end expansion.  Too little force will result in tube sheet leaks, while too much force will lead to early tube failure.  Here are some simple steps to assure the rolling operation is done correctly.

1. Review the sample calculation that is posted on Heat’s web site.  The actual measurements can be entered into the formula.  The only assumed  value is- % wall reduction.  This % will vary from 4-10%, depending on the material of the tube sheet and the new tubes.  Please contact us if you need a recommendation for this factor.
2. Once the calculations are made, use a properly serviced torque controlled rolling motor and expander to determine what torque is needed to achieve the proper wall reduction.  Once you have the proper torque, monitor the rolling operation by comparing the calculated inside diameter of the tube to the actual inside diameter.  You should check at least every 50-100 tube ends to insure that the tube expansion is correct.  Please note that the measurements need to be taken on both tube sheets.  You  must measure the diameter of both tube sheet holes before rolling the first end.
3. Heat recommends that one person per shift be assigned to take these measurements.  This person should have the authority to stop work, if the actual calculations do not closely match the calculated values.
4. Finally, insure that the people performing the rolling operation each have two expanders in good working order.  Expanders used continuously will become hot and fail.

As always, please feel free to email me at alan.miller@heatinternational.net or via telephone at 770 607 3781, x11.