By Ed Nunes
The Water Department at San Francisco Water Power Sewer (SFWPS) provides water services to the 2.6 million residents of the greater Bay Area, and manages retail drinking water for San Francisco and wholesale water for three Bay Area counties.
Underground digging on subway tunnels triggered a large sinkhole in the South of Market neighborhood of San Francisco, a very densely populated area with heavy traffic. The sinkhole measured 50 feet wide, 75 feet long and 40 feet deep. The resulting falling debris damaged the cast iron pipe that had been originally installed almost a hundred years ago. The pipe was left exposed with utility lines channeled alongside the piping left unsupported, further putting pressure on the pipe.
The Challenge
The piping needed to be quickly repaired to restore water service so that street-level traffic could resume. The piping ran between a number of concrete utility vaults and had a pressure rating of 300 psi. A coupling was required that could safely handle the high water pressure so that entire lengths of piping between the vaults would not have to be replaced. Such an operation would have required connecting the pipes with lead joints, a very time-consuming and labor-intensive process. With more piping to replace, the labor and material costs would be enormously higher compared to repairs where only sections of pipe needed to be replaced.
The Solution
Richard Gonzales is the superintendent of construction, maintenance and operations for SFWPS and oversees the Water Department and High Pressure Fire System for the city’s public utilities commission. He and his team of engineers decided that using the 12” HYMAX coupling would make the repair faster to help return the street to its usual state while minimizing costs.
The pressure rating for the HYMAX coupling was 350 psi, which was more than enough to maintain the integrity of the pipe. Instead of having to remove and replace six lengths of cast iron pipe, Gonzales’s crew was able to simply replace only damaged sections with new sections of pipe connected on either side with HYMAX couplings. Instead of a process that could have taken weeks to repair, pipe repairs and filling in the sinkhole was completed in a matter of days. The coupling provided three major benefits for SFWPS:
Strength: This was the critical factor in Gonzales’s decision. The 350-psi pressure rating made it possible to use a coupling for the repair instead of removing and replacing entire lengths of pipe between vaults. “I could not find any other coupling that could handle the high water pressure,” said Gonzales. “The HYMAX offered the strength necessary to make the repair. Without it, labor costs would have skyrocketed, paving material costs would have tripled, and we might have had to de-energize power lines, causing disruption for businesses in the area.”
Dynamic Deflection: The Bay Area is subject to occasional occurrences of seismic activity. The HYMAX offers four degrees of dynamic deflection on each side, allowing pipes to shift while maintaining a tight seal. This in essence gives the pipe shock absorbers to withstand the stress caused by ground movement. In many cases of installations using rigid couplings, ground shifts can exert recurring stress on the section of pipe near the coupling, causing it to break or crack. With the HYMAX, the connection can more easily absorb ground movement and reduce the risk of future breaks.
Ease of Installation: The HYMAX coupling features two bolts, compared to more bolts on most traditional couplings, which made it easier for Gonzales’s crew to connect it. They didn’t have to reach around the pipe to secure the coupling because the two bolts were top-facing, meaning they could be tightened more quickly. This was critical because the utility lines for telephone and power were in close proximity to the pipe. “Without the top-facing bolts,” said Gonzales, “it would have been impossible to close the coupling given the channeled utility lines running alongside it.”
Conclusion
The HYMAX coupling offered three distinct advantages for SFWPS. The coupling’s durability to withstand high pressure allowed the repair to be made quickly while minimizing disruptions to traffic, power and telephone line service. The coupling’s top-facing bolts made it possible to install the coupling in an environment that allowed little space to connect traditional bolt connections. Finally, the dynamic deflection capacity helped ensure that the repair would last, despite shifts in the ground due to seismic activity.
About the Author: Ed Nunes is a product manager at Krausz USA, the creator of HYMAX. To learn more, visit krauszusa.com.
