Intermountain Power Service Corporation

Intermountain Power Service Corporation Unit 1 and Unit 2 fan stack repairs

Project Description
Reinforcing steel corrosion of the outside face of twenty four separate 24 foot diameter, 4.5 foot tall reinforced concrete fan stack “rings” required partial depth concrete repair. Installation of an epoxy coating on the concrete interior eliminated the vapor transmission and stopped the corrosion cell. Access to the inside of the fan stack required professionally engineered steel supports and planking. Safety in the power plant is extremely important and personal safety and tie-off requirements were fulfilled. Coating surface preparation was completed using 20,000-psi water wands. Partial removal of joint grout and joint waterproofing was completed. Two thousand four hundred square feet of partial depth concrete spall repair were completed. Fifteen pound chipping hammers were used for bulk concrete removal. Dry sandblasting with appropriate respirator equipment was used for surface preparation. Dry mix shotcrete was used as the repair material. Average repair thickness was 4-inches. Scheduling was extremely critical. Access inside the stacks, 1980 lineal feet of joint repair, 2100 lineal feet of epoxy injection, 13,500 square feet of surface preparation and epoxy coating was completed over a 4 week period during plant shutdown. Concrete repairs were completed after operation start up. Subsequent testing proved effectiveness of corrosion reduction

Field Problems Encountered

  1. Discovery of previously un-identified crack created changed site condition. Added epoxy injection of cracking to scope of work and changed other detailing to offset increased cost of work.
  2. Concerns prior to letting of contract regarding concrete out gassing and subsequent bond of coating were alleviated by taking water vapor transmission tests prior to coating application.
  3. Concerns of concrete substrate temperature and effect on concrete to concrete bond in partial depth patches alleviated through tensile bond pull off testing of concrete repairs.

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