Trenchless Relining Doubles Lifespan of Don Pedro Dam's Aging Penstock
A specialty coating contractor relined a 50-year-old steel penstock at California’s Don Pedro Dam instead of replacing it, Trenchless Technology reports, extending the asset’s service life by another half century.
Market Impact
The penstock, 16.5 feet in diameter and roughly 1,300 feet long, sits 300 feet below ground and feeds water to turbines generating 203 megawatts at the hydroelectric facility jointly owned by the Turlock and Modesto Irrigation Districts. The relining work is part of the Don Pedro Project’s Life Extension and Upgrade Program, launched in 2010 to bring aging plant components back to like-new condition.
The bidding process itself signaled how few contractors are equipped for this kind of work. Owners solicited proposals from 15 heavy industry coating contractors and received exactly one bid, from F.D. Thomas (FDT). The pipe’s geometry, including a 53-degree sloped section requiring custom suspended scaffolding, and two narrow 45-day outage windows across 2020 and a following year, limited the field to contractors with specialized rigging and confined-space capabilities.
FDT relined about 500 feet of pipe in the first campaign, then built a full-scale wooden mock-up to test rigging and access methods before tackling the steep section. Crews battled water infiltration of roughly 125 gallons per minute even with gate valves closed, requiring a temporary catch berm and pumps to move water 300 feet back to the reservoir, plus a 200-foot staircase for access. Surface prep hit SSPC-SP 5 white metal blast standards using both manual and robotic methods, and crews applied Sherwin-Williams’ Sherplate PW Epoxy, a 100% solids lining, to a minimum 30-mil dry film thickness. The coating’s 14-day recoat window and 24-hour return-to-service rating let crews keep working almost until each outage deadline.
What It Means for Subcontractors
- Specialty coating and lining subs who can staff confined-space blasting crews, build custom rigging, and hold containment for lead-based legacy coatings have real pricing power: 14 competitors passed on this bid, leaving FDT as the sole responder.
- Water and hydropower asset owners running life-extension programs (like the Don Pedro Project since 2010) are choosing rehab over replacement for major steel components, a signal for subs to pitch relining packages against full pipe replacement on similar aging penstocks and interceptors.
- Crews bidding fixed outage windows should budget for mock-up testing (FDT built a full-scale wooden replica before working the 53-degree slope) and backup power for dehumidifiers, heaters and dewatering pumps, since a single power loss can shut down a tight 45-day schedule.
- Subs specifying lining systems for immersion service in confined spaces should note the value of fast-cure, solvent-free epoxies like Sherplate PW, whose 14-day recoat window and 24-hour return-to-service rating directly protected schedule on both outage campaigns.
- Third-party inspection firms such as Bay Area Coating Consultants, which verified prep, environmental conditions and film thickness on-site, remain a standard fixture on these contracts and a route for QA/QC subs to get embedded in similar dam rehab work.
