John Butterfield - 13 August 2015
The Gateway Arch in St. Louis was made out of stainless steel fifty years ago. It seems at the time the most logical choice in order to achieve its desired longevity, not to mention the necessary aesthetic requirements of the architects. Today it is celebrated for its elegant symbolism and incredible size but at the time of its build it was also innovative and visionary, being the world’s first large structural application of stainless steel.
Catherine M. Houska of TMR Consulting from Pittsburgh, USA lately reported in the Stainless Steel World magazine (July/August edition) on the state of St. Louis’ Gateway Arch. Whilst it appears that the original metal chemical certifications of the type 304 stainless plates and weld filler used for constructing the arch can no longer be traced (the mills that produced the plate are now part of the corporate history of ATI Allegheny Ludlum and Outokumpu), these companies were able to provide information on the testing capabilities of the time period of the build though type 304 stainless plates would have been prepared in the 1960’s according to ASTM A167. Likewise, information about the source of the filler metal used in the welds also no longer exists. However, welding procedures qualifications, and records for the horizontal and vertical butt joints show us that MIG welding was used with different argon–carbon dioxide helium cover mixtures for each joint orientation at the time of construction. Similarly, the welds were cleaned up with a wire brush and two weld passes and a grooved back up root treatment were used. Further, a Pittsburg–Des Moines Steel Company letter from December 1963 informs us that weld haloes were removed using electrolytic methods. Electrolytic cleaning wands were used fifty years ago. Although it is an old technology, it is still in use today, techniques not having changed very much. It was most likely used in combination with brushing to restore corrosion resistance. Moreover, the cleaner used, Oakite 33 which is a phosphoric acid-based, is also still used. In connection with the St. Louis Arch, the technique was used to clean and degrease the surface of the plates prior to welding. Additionally , both AWS and ASME code Section IX were referenced in the weld procedures.
To find out more about the actual construction of the St. Louis Gateway Arch and how its corrosion resistance holds up today, please read the full article.