Warning - Hot work can ignite titanium tube bundles


		AcuSafe -> August 2000 Newsletter
		Warning - Hot Work Can Ignite Titanium Tube Bundles

There are hazards of doing hot work on titanium heat exchanger tube bundles. The metal itself can ignite and sustain combustion - just like aluminum or magnesium. Although there are only a small number of reports of this phenomenon, it is easy to avoid and ensure your site is not added to the statistics.

Background
Titanium tubes are sometimes used in the chemical and petroleum industry where brackish cooling water is encountered and 'admiralty' materials cannot be used for process side reasons. While according to Mr. Mahnken, "titanium is considered a combustible metal and , yet, it is also widely used and successfully used in high temperature equipment such as heat exchanges and distillation columns as well as for aerospace applications." Remember the SR-71 blackbird?

Ignitions Sources
The problem presents itself in the processing industry when maintenance work is done on the out-of-service equipment - often times in a shop environment. The mechanics, being well trained on the hazards of hot work, ensure that the bundles is clean and contains no combustible residue. Gas testing and visual examination confirm this. But slag from an oxyfuel cutting torch can cause a piece of hot slag to become a little thermite reactor where the Iron oxide in the slag can combine with the titanium and release heat.

"According to Mr. Mahnken, "Once a small area of metal is ignited, the incipient tube bundle fire will either self extinguish after a short period of time or else it will continue to grow and burn intensely until all the combustible materials are essentially consumed"

Fire Protection and control
The article goes on to say "There is no known reliable method of extinguishing a fire that has established itself in a titanium tube bundle". Water is of no use and can even lead to a subsequent, more damaging explosion. "Carbon dioxide, nitrogen, foam, and dry chemical extinguishers are not effective on titanium fires. Incipient fires might be controlled or extinguished using a class D portable fire extinguisher, dry metal powder, flux or dry salt." Fully involved bundles will just have to burn themselves out, often taking the surrounding structure with them..

Prevention
The first step is to ensure that your work practices recognize the hazard of doing hot work on titanium heat exchanges. Although signs can be used, experience on Process Hazard Analysis Studies (HAZOPs) indicates that the average life of any warning sign is only about five years. So other steps should include: notes in the equipment files, comments on P&ID's, and a warning step in the general hot work procedures.

Assuming that the hazard is recognized through these steps, a formal job hazard analysis may indicate that doing cold work is a better option to accomplish the task. Conducing the work outdoors rather than in the shop may offer better personnel protection with easy evacuation and scene control in the event of the ignition of the tube bundle.

Conclusion
Mr. Mahken reports that in at least one case, the owner of a heat exchanger that caught fire during demolition was issued a citation by OSHA (subsequent rescinded) for not providing a MSDS on titanium to the contractors doing the hot work. With that little smile of your face, ensure that the prevention steps mentioned above are in place and you don't add your facility to the list of places that have not recognized this hazard.