U.S. Air Force Memorial
Problem: A Demanding Structural Application
The $30 million U.S. Air Force Memorial in Arlington, Virginia,
with its soaring spires, is one of the most demanding structural
applications for stainless steel built to date. Weighing 17,000 tons
and incorporating three stainless steel spires (the tallest of which
soars 270 ft. high), the design of the memorial had to take into
account significant forces of wind and vibration, as well as
corrosion problems from weather, water, and road salts.
The memorial’s stainless steel finish was particularly
demanding, as it needed to appear seamless, have the right level
of reflectivity for nighttime illumination, and yet not blind pilots
flying into nearby Washington, D.C. with its glare in the daylight.
Solution: The Expertise of Outokumpu in the Design Process
The structural design phase of the memorial took more than a year and included elaborate modeling
and wind tunnel testing. Throughout the design process, Outokumpu staff at our New Castle, Indiana
plate mill consulted with the project’s engineers and created models to help the design engineers
understand what was possible in terms of plate flatness, width, and possible surface finishes.
Solution: 316L for Corrosion Resistance and Superior Welding Performance
Working in concert with the service center Rolled Alloys, Outokumpu’s New Castle plate products facility provided
approximately 345 tons of 0.770” thick 316L stainless steel for the memorial. (The specifications called for a thickness of 0.750”, so
Outokumpu delivered 0.770” thick plate to allow for polishing.) The hot rolled annealed and pickled plate material was produced with
low sulfur content (to 0.001 max ) for improved corrosion resistance, better internal cleanliness, and improved surface finish.
The stainless was melted to Outokumpu’s low inclusion content practice to minimize the possibilities of exposing non-metallic
inclusions during the polishing process. (Exposed non-metallic inclusions can serve as crevices for the initiation of corrosion and are
also visually detrimental.) In order to facilitate the subsequent polishing process, the plates were also produced to 1/2 commercial
flatness tolerance (with an additional intent by the mill of reaching 1/4 commercial flatness tolerance).
316L was specified for the memorial for several reasons. First, the memorial (with three different highways along its property border)
will come in contact with road deicing products. Although this exposure is expected to be minimal, the final surface finish is fairly
rough and will therefore retain more dust, salt, and pollutants than a smoother surface finish. So a higher level of corrosion resistance
was necessary to counterbalance the rough surface finish. Second, the welds on the memorial are structurally critical, so it was
important to use a stainless steel grade that would be easy to weld and repair if necessary.
To achieve the desired surface finish, one that would reflect architectural lighting during the night but also meet daytime reflectivity
requirements of the nearby airports, a multi-step finish was specified. The plate was first polished to a 50 grit finish for a uniform
starting finish. After the sections were welded together, the plates were then pickled to create a dull substrate and to further improve
corrosion resistance (eliminating any micro crevices from polishing, surface contamination, and restoring weld corrosion resistance).
The final step was a fine glass bead blasting process that changed the surface texture but did not remove any metal (so as to retain the
pickling benefits). The final result, a corrosion resistant, finished metal reminiscent of the “skin” of an airplane.
Solution: The New Castle Commitment to On-time Delivery and Quality
The New Castle team worked hard to meet the strict quality and delivery requirements for the memorial. All of the plate was delivered
within a 10-week time frame. Not one plate was rejected for non-conformance. All dimensional tolerances and surface conditions were
produced exactly as specified.
Solution: Special Damping Challenges of the U.S. Air Force Memorial
The memorial’s design, by internationally renowned architect James Ingo Freed, of Pei Cobb Freed & Partners, was intended to evoke
a flying spirit and the precision of the “bomb-burst” formation made famous by the U.S. Air Force Thunderbirds.
One of the most daunting structural aspects of the design was the “damping” of the spires to make sure they didn’t literally shake
themselves apart in the high winds that can occur at 270 feet. The engineer’s damping design used 13 boxes stacked in the spires,
each containing a 20-inch diameter, 2,000-lb. metal ball encased in a stainless steel shell. The balls roll within synthetic damper pads.
As the balls impact the damping pads, energy is dissipated and structural movement is constrained.