Insulation, Part 3: Minimizing Fire Hazard Using Mixed Insulation Materials
Reduce Insulation Fire Potential While Controlling Cost
Although it almost eliminates the potential for insulation fires, good quality cellular glass insulation (like FOAMGLAS) is significantly more expensive both to purchase and install than the mineral fiber (fiber glass or glass wool) or compressed particle (calcium silicate or perlite) type materials. The trick to “optimizing” insulation costs is to utilize cellular glass where it is necessary and use the less-expensive material where there is minimal potential for fluid leaks (if you get a leak on a uninterrupted pipe run you’ve got bigger problems than soaked insulation). Typical high-potential leak areas include valves, Y‑strainers and any pressure taps or other connections where fluid could potentially leak. Fiber glass or calcium silicate can be used anywhere else.
Transitions from one type of insulation to another are critical.
Horizontal pipe runs can transition at flanges or 12-18” from the “leak” point. If you want to keep the cladding intact, it’s a good idea to leave 1-2” of space between the insulation and the flange so that you can retighten the bolts once the system is at operating temperature. The open end of the insulation should be sealed to prevent any spills from above from leaking into the mat. Sealing the end is critical where the transition occurs on vertical pipe runs since any leakage will run along the pipe under the cellular glass.
For short vertical runs, “optimizing” the insulation might dictate skipping the transition until the horizontal run starts—where thoroughly sealing the open end is less critical. Just a reminder — never insulate flanges in a hot‑oil system. If the bare flange presents a safety issue, install a protective sheet-metal cover with a drain hole. There are also removable modular cladding/insulation systems which are non-permeable that can be installed over flanges (these also work well for valves and Y-strainers).
Insulation Thickness, Heat Loss, and Savings for Varied Pipe Sizes at 500ºF
Minimizing fire hazard from insulation is very straightforward — but the materials can be more expensive than conventional insulation.
Once the equipment is up and running, the insulation should be inspected periodically to make sure that there is no fluid leaking into it. Any visible smoke or odor of hot fluid should be investigated. Weep holes should be drilled into the bottom of the cladding to allow leaked fluid to escape. Any darkening of the insulation or cladding indicates that fluid is leaking. Insulation that has been soaked with fluid should be removed carefully since any sudden increase in the oxygen level can result in autoignition.
Related Article: Recommended Hot Oil System Components