29Apr 2015

Combating Microbial Corrosion in Tunnels

By Robert Armstead

Microbial corrosion, or microbiologically-influenced corrosion (MIC), is “the gradual damage to metal caused by the metabolic activity of microorganisms.”  This corrosive damage has caused billons of dollars of damage to our water systems, especially our storm water and sewer systems, although MIC can happen wherever metal and water meet.  Finding a solution for repairing corrosive damage depends on where it is occurring, why it is occurring, and how disruptive or expensive a repair or replacement will be.

There are several different types of bacteria responsible for MIC in metals located in soils and water; all are classified as either aerobic (requires oxygen) or anaerobic (oxygen is toxic). Sulfate reducing bacteria (SRB) is anaerobic and is responsible for most of the corrosion caused to steel in sea water; whereas, iron and manganese oxidizing bacteria are aerobic and are most often responsible for the rapid corrosion and pitting at welds in stainless steel.  Microbial corrosion can also occur in plastics, concrete, and many other materials.

Water leaking through the corroded metal liner of the tunnel.
Water leaking through the corroded metal liner of the tunnel.

In a recent project at the University of Oregon in Eugene, Oregon, URETEK Holdings was brought in to help the engineering firms of KPFF and GRI strengthen and seal the east utility tunnel which was experiencing MIC.  Campus operations had been dealing with a large water infiltration problem that was causing the corrosive damage.  To make matters worse, there was an ever increasing flow of water into the tunnel calculated at approximately 40 to 50 GPM.

Water invades the top of the tunnel because of corrosion.
Water invades the top of the tunnel because of corrosion.

There are several ways to combat corrosion, including:

  1. Regular mechanical cleaning;
  2. The use of corrosion inhibitors to combat the growth of the bacteria; and
  3. Complete drainage and drying out the environment.

Since replacing the tunnel was not an option for the University of Oregon, it was necessary to dewater the tunnel so that it could dry out, increasing its lifespan.

URETEK Holdings’ project manager, John Schmidt, worked with the engineers at KPFF and GRI in preparing a plan for stopping the flow of water into the tunnel.  The plan included injection of polyurethane into the target area to fill the voids in the soils around the tunnel, basically plugging the pathways of the water flow into the tunnel.  The injection points were spaced at predetermined intervals and at specified depths. URETEK’s Deep Injection® Process successfully decreased the water flow into the tunnel to drips, which will allow the tunnel to dry out, creating a less favorable environment for MIC.

Corrosion Fundamentals. (n.d.). Retrieved April 14, 2015.