Worries that the dazzling arch in St. Louis at the Jefferson National Expansion Memorial was experiencing some structural fatigue have been allayed by an analyis that shows staining on the arch is superficial and can be remedied.
In studying the stains, the engineers also looked at other stainless steel structures of roughly the same age to see if they also were exhibiting staining. Those studies "revealed that other stainless steel structures have not suffered the same exterior staining as the Arch, leading the engineers to believe that the welds that hold the Arch's sections together may be the culprit," a park release said.
"The Gateway Arch stands alone from other buildings and monuments researched in its extensive use of shop and field welds," the engineers stated. "Many of the discolorations of concern are caused by atmospheric pollutants or inadequate cleaning and polishing of the Arch after erection. In addition, if a metal other than the exact type of stainless steel the Arch is made of (Type 304) got into the welds when they were made, the rogue metals might be the cause of the staining."
The report notes that whatever the cause, the corrosion is natural and minor, and does not threaten the integrity of the welds or the structure, park officials said.
However, they noted that "another problem is posed by the unfortunate and growing habit of visitors who carve their names into the exterior base of the Arch legs. The carved graffiti (which is a federal offense) shows streaking similar to the welds higher up, and will also be treated to try to eliminate it and to repair the damage," the release said. "The cleaning of this graffiti might be followed up with a clear coating of some type to prevent future damage."
Recommendations made by the engineers to eliminate the streaking on the exterior of the Arch include further close-up testing of the welds to determine the best method of cleaning the metal and stopping the streaking at its source. Samples will be taken from the exterior of the structure and studied to determine the exact type of corrosion present. This would be followed by the final step, a gentle cleaning of the stainless steel surfaces and dressing and polishing the original welds to reduce future staining. Lower welds will be easier to reach than those higher up, and some sort of rappelling solution, similar to what was recently done on the exterior of the earthquake-damaged Washington Monument, may be necessary to reach the upper welds.
Memorial Superintendent Tom Bradley called the engineers' report "good news for all of us."
"We now know that St. Louis's most iconographic structure is in good health," he added. "The Arch may be a little discolored in some places, but we are now certain that it is part of the aging process, and we will work to keep this one of a kind structure in the best shape possible for future generations. It may take some time to get up there to clean it, but we will get it done."
The effort to address the staining is part of the ongoing maintenance and long term stewardship responsibilities of the National Park Service and is separate from CityArchRiver 2015, a project currently under way to enhance the visitor experience and better connect the park to downtown St. Louis.