THE LAWS OF PHYSICS ARE IMMUTABLE. It's Instalanched: the Gateway Arch is corroding.

Topped out in 1965, the Arch is made up of triangular sections — a carbon steel interior and stainless steel exterior — stacked and welded one atop the next. Concrete reinforces the lower half of each leg.

"It is possible that corrosion at welds or at contaminated areas
is taking place aggressively," one report said.

The investigation noted a repainted area inside the south leg. "Failure of the original paint layer in this area may have been due to rusting of the steel," the report said.

It suggested taking core samples of the metal for testing, but warned that, "Removal of stainless steel from the Arch will be controversial and will require planning and much discussion."

Water intrusion has long been an issue. "Condensation in the
legs has been there since day one," [Jefferson Memorial deputy superintendent Frank] Mares said.

Stainless steel and carbon steel are chemically different enough that an electrolyte between them induces electrolysis. Concrete absorbs water: there's your electrolyte.

If the designers of the arch were in the same social circles as managers of the Missouri Pacific Railroad, they might have been alert to the problem as they designed the arch. One reason most of Amtrak's initial purchases, including the baggage cars and dining cars still running, are Budd Shotwelded cars, is that by 1971 the stainless-steel clad Pullman and American Car and Foundry cars running on Missouri Pacific and a number of other railroads had serious corrosion of their inner shells. The inner shells were Cor-Ten carbon steel, there was a layer of insulation between the inner and outer shells, and the outer shells were stainless steel panels. As built, they were as shiny as Budd's cars, but with exposure to the elements, they turned into 85 foot long voltaic cells. Missouri Pacific were aware of the problem before Amtrak came into being.