Sewer Lids corrode from Hydrogen Sulfide gas exposure, water and salt, destroying the iron strength properties. Improvements in stormwater infiltration prevention have made sewage less dilute, and H2S more concentrated. Fats, Oils, and Grease (FOG) in grease traps also contribute to severe H2S production. H2S is converted to sulfuric acid by bacteria in the sewer system.
"...the total annual estimated direct cost of corrosion in the U.S. is a staggering $276 billion" Source: “Corrosion Costs and Preventive Strategies in the United States,” U.S. Federal Highway Administration (FHWA), PUBLICATION NO. FHWA-RD-01-156
Perhaps regulators should include H-20 / H-25 Proof Load re-certification by sampling existing covers at age intervals and institute scheduled replacement based on predicted corrosion rate with various PPM levels of H2S. Otherwise, do we trust that current iron covers in-ground are safe?
This photo shows stacks of CAP covers and iron covers at a local supply house. The oxidation on the iron covers starts even before installation. Some claim that this "patine" actually protects the covers, but experience shows that this far from enough.
Testimonial - Cracked Covers Are Left in the Streets
One public utility supervisor recently admitted to CAP that workers sometimes crack covers during the hammering to dislodge them from the frame. The operators feel they have done something wrong, and to avoid punishment, they would rather not tell anyone about the cracked cover and leave it in the street...waiting for the next unsuspecting driver or pedestrian!
Corrosion bonds the iron covers to the iron frames. Municipal workers commonly slam the edges with a sledge-hammer or melt it with a flame torch to dislodge the cover from the frame. This causes fracturing in the already corroded covers. Hydrogen Sulfide has riddled the cover with corrosion from the bottom, and the subsequent sledge-hammering from city workers finishes the job from the top.
Testimonial - Manholes with Fused Covers are Not Inspected
A director for a wastewater collections department indicated to CAP that when he sends his operators out to do inspections that they will often skip inspecting the manholes that they cannot open without a hammer or flame torch. That means that many of the manholes that probably need it the most do not get inspected!
" Brand received a letter from MSD explaining a crew went to the site and found a broken inlet cover, and replaced the cover. A second letter was sent from Corporate Claims Management Inc., which handles MSD’s liability claims. The company explained MSD had no prior notice of the condition of the manhole, therefore are unable to accept responsibility for injuries"
During a replacement, city workers observed that the cover support on the frame had entirely corroded away realizing why it was "sinking."
Another cover in a Rio Grande Valley children's park scared local residents enough to photograph the incident and send to CAP.
Many inquire about the weather resistance while ignoring the more frequent reason for replacements - acid exposure under the cover.
Corrosion can get so aggressive that remnants of the oxidized iron are left on the concrete below the frame.
The material used in CAP's covers is also selected to use in frames and hangers in the electrowinning cathode/anode reaction. In this copper purification process, copper sheets are held with composite supports inside a sulfuric acid tank. While the acidic vapor eats through most materials, CAP materials resist the high concentrations of sulfuric acid vapor exposure.