As an engineer, how do I design steel lintels for exterior brick masonry so that corrosion is not a problem?
To compensate for corrosion, many engineers specify steel lintels with a plate thickness of at least 1/4 inch or even 5/16 inch. If the steel area required by design is greater than 5/16 inch, some engineers add an extra 1/16 inch to allow for corrosion. According to Fontana and Greene, Corrosion Engineering,* typical corrosion rates for steel exposed to the atmosphere, industrial and marine, are 1 and 5 mils per year, respectively. A mil is 0.001 inch thick. An extra 1/16 inch (62.5 mils) of steel adds 62 1/2 years of service in industrial environments and 12 1/2 years of service in marine environments. The Brick Institute of America (BIA) suggests using galvanized steel lintels in harsh climates, such as in marine exposures.** Galvanized steel lintels do not require the periodic maintenance often required by ungalvanized steel lintels. Galvanized steel lintels cost more, however. In Colorado, they can cost about 28› per pound more than plain steel lintels. Because harsh climates are never well defined, we suggest you inspect steel lintels on some old buildings in your area. If you find little corrosion, specify ungalvanized steel lintels. Select the lintel that meets the minimum steel area required by design--or to be safe increase the thickness by 1/16 inch. If you find extensive corrosion, specify galvanized lintels. * Fontana and Greene, Corrosion Engineering, 2nd Ed., 1978, McGraw-Hill, Inc., New York. ** BIA Technical Note 31B, "Structural Steel Lintels," Brick Institute of America, 11490 Commerce Park Dr., Reston, VA 22091.