SYMPOSIA PAPER Published: 01 January 1989

Pressurized Flammability Limits of Metals


The combustion of seventeen metals was studied using a pressurized oxygen index apparatus. The procedure measures the metal's flammability limits (minimum concentration or minimum pressure that enables equilibrium combustion). Metals tested included 201, 304, and 430 stainless steels, copper, brass 360, Monel® 400, carbon steel, 9% nickel steel, Incoloy® 800, Inconel® 600, Stellite® 6, and to a lesser extent, 316 and 410 stainless steels, zinc, titanium, and Ti-6A1-4V. Vertical rods 6.4-mm (0.25-in.) in diameter were principally studied, although some 3.18-mm (0.125-in.) rods and 6.4-mm (0.25-in.) diameter, 0.89-mm (0.035-in.) wall tubes were also tested. Tests of 304 rods were also conducted with specimens at up to 90° to the vertical to assess the effect of melt drainage patterns. In all cases, the tests explored upward propagation against a small downward gas flow at gage pressures to 10.34 MPa (1500 psig).

Metals were ranked in the following order of lowest to highest compatibility: aluminum, carbon steel, 9% nickel steel, 10.5% aluminum bronze, zinc, 201, 304, 430, and Incoloy® 800, which exhibited propagations at pressures below the 10.34 MPa (1500 psig) limit of the apparatus. Stellite® 6, brass 360, Inconel® 600, copper, and Monel® 400 all resisted propagation at the maximum gage pressure of 10.34 MPa (1500 psig).

Stainless steel 304 rods exhibited much greater thresholds than did tubes; whereas carbon steel rods and tubes produced more nearly equal thresholds. Alloy 304 also exhibited much lower thresholds after annealing and exhibited the lowest threshold with a vertical orientation. An approach to using these and other data to support increased usage of 304 is reviewed.

Author Information

Zabrenski, JS
Air Products and Chemicals, Inc., Allentown, PA
Werley, BL
Air Products and Chemicals, Inc., Allentown, PA
Slusser, JW
Air Products and Chemicals, Inc., Allentown, PA
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Developed by Committee: G04
Pages: 178–194
DOI: 10.1520/STP24927S
ISBN-EB: 978-0-8031-5095-9
ISBN-13: 978-0-8031-1288-9