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Hot work during repairs can unexpectedly ignite bundles of this and other metals, setting off fires that can burn uncontrollably. However, prevention is possible.
Titanium alloy tubing is widely used in chemical process industries (CPI) and utility plant heat exchangers, where the metal does not normally present a fire hazard, even at temperatures well above equipment design ranges. However, loss reports indicate that hot work conducted on heat exchangers containing titanium tube bundles has resulted in severe metal fires and explosions (1, 2).
Conditions that can cause ignition of a metal tube bundle are predictable and preventable. Increased recognition of this hot work fire/explosion hazard is the key to thwarting future incidents.
Typical scenario
Based on reports for a small number of reported incidents, a titanium metal fire caused by hot work on a heat exchanger develops according to the following sequence of events:
1. A heat exchanger containing titanium tubing is taken out of service for repairs or modifications, is planned to be dismantled, or is sold to a scrap metal processor.
2. The exchanger has a steel shell. The unit could be relatively small - approximately 6 ft long, containing a 3-ft dia. bundle with several hundred tubes. Or, it could be a large steam condenser, with a tube bundle that is 25-ft long, several feet in dia., and holding thousands of titanium tubes.
3. Planners determine that workers will have to cut open the steel shell of the heat exchanger to repair or remove the bundle.
4. The fire hazard associated with torch cutting on, or near, titanium tube bundles is not recognized.
5. The presence of titanium tubing inside the heat exchanger is not even known. In one case, a steam condenser had been retubed with titanium 20 years earlier, and there was no recollection of the change of materials until after the fire.
6. Preparations for hot work are made. Strict fire safety precautions are taken, such as:
a. Restricting access to the work area to essential personnel only.
b. The person in charge of issuing the hot work permit carefully checks the heat exchanger and surrounding area to verify the absence of combustible vapors, oil, flammable liquids, organic residues, or other known combustible materials (except for titanium!).
c....