" Wax Job" Evaporator Retube

“In 1982, PSF Industries was working on a project at International Paper in Gardner, Oregon when the manager of maintenance, Jack Williamson, came to us with a problem concerning his black liquor evaporators.  His existing set of evaporators were fabricated out of carbon steel with carbon steel tubes.  Five years earlier the carbon steel tubes had failed and PSF Industries retubed the evaporator with stainless steel tubes.  Now the top tube sheet that the tubes mechanically roll into had failed.

The problem we were confronted with, as we sat around the table with Jack, was how to save the new existing stainless steel tubes that were still good while replacing the tube sheet with a stainless steel tube sheet.  The traditional method was to remove the 1,200 existing tubes, then remove the existing tube sheet, then reinstall a new stainless steel top tube sheet and then reinstall 1,200 new stainless steel tubes.

First we had to come up with a way to interior-cut the 1,200 tubes off at the bottom side of the top tube sheet and still save the tubes.  Then we had to hold the 1,200 tubes in place.  Because there were no baffles between the bottom tube sheet and the top tube sheet, once you cut the tubes off they fall together and it is impossible to line them up to install the new tube sheet.

The method we devised for doing the top tube sheet began with filling the vessel with water up to about three to four feet from the top.  Next we heated it up with steam to about 190 degrees.  Then we rented a wax melting pot from a candle maker and bought bulk wax.  We melted the wax, cut a hole in the top tube sheet and poured the wax in on top of the water.  The wax floated, making a temporary 12” thick tube sheet that held the tubes in place.

Next we developed an interior one-revolution tube cutter and sharpened it to save the top of the existing tube.  We proceeded to internalcut off the 1,200 tubes.  Then we cut the tube sheet loose the shell and removed it.  The next step was to clean up the tube ends and round up the tubes.  Then we installed the new stainless steel tube sheet (fabricated by our shop in Seattle), guiding it over all 1,200 tubes and dropping in into place.  The next step was to weld the new stainless tube sheet to the existing carbon steel shell.  Then we mechanically rolled the existing stainless steel tubes into the new tube sheet.  We emptied the water out of the vessel and heated the vessel up and melted the wax.  After we drained the wax out of the bottom into barrels, we gave it to the mill employees so they could make candles with it.

This process saved the mill from buying 1,200 new stainless steel tubes.  That was a savings of $92,000.  The job was done in six days by working around the clock.  We ended up buying the candle maker’s melting pot.  We’ve done this procedure on the top and bottom tube sheets several times at different mill sites.  It shows how creative we can sometimes be when we all get together and start talking about a particular problem”.

Stanley R. Miller
President