ARNOLD AIR FORCE BASE, Tenn. – When it’s possible to increase operational reliability while minimizing the cost and disruption caused by maintenance, it’s a win-win.
Arnold Engineering Development Complex team members are implementing a trial run of such a solution to the problem of leaks in raw water pipes at Arnold Air Force Base. Raw water is used in the cooling systems of the test cells on base.
According to Jeff Quattlebaum, National Aerospace Solutions (NAS) cooling water system engineer at Arnold, the leaks are a result of corrosion causing holes in the steel pipe. The flooding caused when a leak becomes significant impacts pits, manholes and structure foundations; and it causes a safety issue in freezing temperatures.
“The cost of total replacement is roughly 10 times the cost of this repair project,” Quattlebaum said.
Congestion in the underground space with ducting, other utilities and equipment foundations complicates repairs by limiting access to excavate, explained Quattlebaum. This often requires holes to be repaired from inside the pipe and forces base-wide raw water outages of four to six days for each outage.
Outages are costly both financially and in terms of testing time.
“Each outage costs the base tens of thousands of dollars in effort, requires personnel to crawl into awfully long, tight spaces, and AEDC loses significant amounts of potential test time,” said Maj. Michael Knauf, Aeropropulsion operations officer.
Underground congestion also restricts the location of new water lines. The lines being repaired are 72-inches in diameter and 30-inches in diameter.
Above-ground installation poses other problems.
“Installing the pipe above grade would block access to the other systems and equipment in the area,” Quattlebaum said. “
Water piping as large as 72-inch diameter requires significant support structures if installed above grade.”
These difficulties in locating a new line contribute to the high cost of replacement when compared to repair.
The solution – have a subcontractor line the interior of the pipes with a fiber-reinforced polymer, an option that is both faster and cost-saving.
“Part of my job as a servant to this great nation is to find the most efficient and cost effective method to fix any problem that the U.S. Air Force has,” said 2nd Lt. Adam Doyle, a project manager with the Test Systems Sustainment Division. “I believe this project is a step in that direction.”
Using this method, a repair of approximately 450 feet total between the two sizes of pipe was recently completed in about three weeks – a considerable time-savings when compared to the several months needed for replacement.
“Replacing the underground pipes would have significantly impacted testing, because it would have required a raw water outage for six months to one year,” said Corey Jenkins, a NAS capital project manager.
The repair location offered an opportunity to make a base-wide impact with success, but minimize impact if there are any failures of the lining.
“This location was a lower risk candidate than most other locations on base,” Quattlebaum said. “We were experiencing frequent leaks that had a base-wide impact to repair. This line only serves two (Engine Test Facility) test cells, J-1 and J-2, so if the lining does not perform as advertised and comes loose, only J-1 and J-2 testing would be impacted.”
With the repair complete, the sections should be leak free and able to handle full pressure.
“This composite pipe will be as strong as a new steel pipe on its own, having the strength required to withstand the full 150 psi of water pressure, even if the entire steel pipe erodes away,” Knauf said.
It is anticipated the lining will have a 50-plus year lifespan.
“Many people on base are eyeing this project to see what AEDC can take away from this new method,” Doyle said. “This project has the potential to change the way Arnold AFB conducts all its pipe repairs in the future by giving a drastically cheaper and time-effective method.”