By Peter M. Tallman
It is common knowledge that many heat exchanger (HX) tube failures occur within the first 6 in. (150mm) of the bundle. Inlet-end erosion, stress corrosion cracking, and crevice corrosion are different types of failure mechanisms that are common in shell-and-tube HX.
In the past, the accepted repair for heat exchanger (HX) tube damage localized close to the inlet was full tube replacement or shortening of the tube buncle - despite the fact that more than 95% of its length usually remains undamaged. Either type of repair has proven extremely expensive and time consuming.
Accordingly, alternatives to full retubing repair long have been sought, including:
- Protecting damaged tube inlets.
- Restoring plugged leaking tubes to active service.
- Restoring original compressive strength to weakened tube-to-tube-sheet joints.
An acceptable repair should be cost effective and extend the life of the existing equipment.
Tube Shields/Thin-Walled Inserts
Metallic, thin-walled inserts or shields were introduced in 1976. They are inserted and then expanded - either mechanically, hydraulically, or by a combination of the two - into the existing tube ends.
Previous attempts to correct tube end erosion/corrosion have included the use of conventional ferrules made of plastic or ceramics. Such conventional ferrules typically are loose-fitting, and normally are cemented or glued in place.
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