On specific applications with high temperatures, inconel inserts with ceramic paper wrapping are also used, where the insert's one end will flared end & the other end will have 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 full length tape. There are two advantages for full length tape, one, higher temperature ceramic paper can be compressed on to the tube insert and 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.