On specific applications with high Temperatures Inconel inserts with ceramic paper wrapping also used, where the inserts one end will flared end & the other end will be with a reverse taper to hold the Ceramic Fiber in between.
In applications where extremely elevated temperatures (1650 F) are present on the tube side of the exchanger care has to be taken not to warp the tube sheet. The use of tube inserts addresses this problem. Typically the tube insert has an hour glass form, creating an air gap between the tube insert and the parent tube. The gap is wrapped with high temperature (2300 F) ceramic paper. The paper is taped in place. We recommend tape full length. There are two advantages for full length tape, one, more high temperature ceramic paper can be compressed on to the tube insert, two, the tape protects the ceramic paper which cannot withstand even minor abuse. Some tube inserts have anchors that become imbedded into the refractory others have pins with ceramic paper to set the tube insert at a specific height from the tube sheet.