Concrete Corrosion In A Confined Space

Cheese Plant, WI

During a routine inspection at a Wisconsin cheese plant, a maintenance person noticed signs of deterioration from erosion and chemical attack inside their recently installed drain water (wastewater) collection manhole.

This manhole was responsible for collecting run-off from the cheese plant’s processes, which included water, chlorinated cleaners, and other unsafe chemicals. If left untouched, the erosion would continue and potentially expose the surrounding soil to their wastewater. This would contaminate the soil and eventually undermine the area around the outside of the manhole.

So, they decided to call on the corrosion experts at Crane Engineering to repair the surface erosion inside the manhole. It was required the repair be completed during the plant’s short downtime window of about 18 hours, which was just two days away.

This project presented an interesting challenge, however. This manhole was a permitted confined space and entering without the proper safety training could be hazardous. 

Confined spaces have one (or more) of the following characteristics:

• Less than 19.5% oxygen
• Flammable/combustible/explosive atmospheres present or able to be generated or enter into the area
• Toxic atmospheres present or able to be generated or enter into an area
• Areas not protected against entry of water, gas, sand, gravel, ore grain, coal, biologicals, radiation, corrosive chemicals, or any other substance which could possibly trap, suffocate, or harm a person
• Poor ventilation
• Restrictive entry for rescue purposes

Abiding by the safety procedures of confined space entry, the Crane Engineering team got to work by first performing their lock out/tag out procedure, and by using an air quality monitor to test the air quality inside the manhole. And, because this was a drain water collection manhole, an inflatable plug was used in the inlet pipes to stop any leftover flow of drain water into the manhole.

Once all was clear, the manhole was dried with a vacuum and the walls were hit with a chipper to remove exposed aggregate that was loose. Surface preparation continued as the walls and floor were diamond ground to clean and provide a bonding profile for the epoxy coating. An epoxy primer was applied to the floor and walls of the manhole, as well as a chemical resistant epoxy liner mortar at 1/8" to 1/2" thick to restore the surfaces to original grade. To complete the project, a chemical resistant topcoat was applied.

The manhole was put back into service within 12 hours from the start of the project. Needless to say, the repair was done on time and safely by following all confined space entry procedures.