After years of recurring steam leakage from the main stop control valve (MSCV), the team identified an uneven casing sealing surface and delivered an in-situ machining repair that restored a reliable, leak-free seal.
The Challenge
Over several years, the D11 steam turbine’s MSCV repeatedly leaked steam from the stop-valve stem section following planned valve inspections. Re-torquing the pressure-seal head clamp-nut bolts would stop the leakage temporarily, but the problem returned after only a short period.
The recurring leak indicated that tightening alone was not addressing the underlying sealing condition. A durable repair required disassembly and a detailed assessment of the pressure-seal head, gasket, and casing mating surfaces.
The Results
The MSCV was disassembled, revealing a deformed pressure-seal head metal gasket that had broken into multiple pieces. Contact checks on the pressure-seal head and casing mating surfaces showed that the casing sealing surface in the seating area was uneven, with minimal contact and poor flatness.
Using an on-site machining vendor, the team machined the casing sealing surface in situ, removing only 0.035 inches to restore flatness relative to the casing’s machined surfaces. Contact checks were repeated after machining. The valve was then reassembled, the stop-valve stroke was adjusted to compensate for the material removed, and all fasteners were torqued to OEM specifications. The completed repair produced a reliable, leak-free valve.
Project information
Location
United Kingdom
Market segment
Power generation
Equipment type
Steam turbine
Equipment model
D11
Restoring a Leak-free D11 Main Stop Control Valve
Location
United Kingdom
Market segment
Power generation
Equipment type
Steam turbine
Equipment model
D11
After years of recurring steam leakage from the main stop control valve (MSCV), the team identified an uneven casing sealing surface and delivered an in-situ machining repair that restored a reliable, leak-free seal.
The Challenge
Over several years, the D11 steam turbine’s MSCV repeatedly leaked steam from the stop-valve stem section following planned valve inspections. Re-torquing the pressure-seal head clamp-nut bolts would stop the leakage temporarily, but the problem returned after only a short period.
The recurring leak indicated that tightening alone was not addressing the underlying sealing condition. A durable repair required disassembly and a detailed assessment of the pressure-seal head, gasket, and casing mating surfaces.
The Results
The MSCV was disassembled, revealing a deformed pressure-seal head metal gasket that had broken into multiple pieces. Contact checks on the pressure-seal head and casing mating surfaces showed that the casing sealing surface in the seating area was uneven, with minimal contact and poor flatness.
Using an on-site machining vendor, the team machined the casing sealing surface in situ, removing only 0.035 inches to restore flatness relative to the casing’s machined surfaces. Contact checks were repeated after machining. The valve was then reassembled, the stop-valve stroke was adjusted to compensate for the material removed, and all fasteners were torqued to OEM specifications. The completed repair produced a reliable, leak-free valve.
0.035 in
Minimal material removed
In situ
On-site surface machining
Leak-free
Reliable valve operation restored
