Large Valve Single Device Isolation Problems & Solutions
Hydro Vision 2008 Turbine Inlet Valve Disc â Casting Plug Failure
Hydro Vision 2008 Turbine Inlet Valve Disc â Casting Plug Failure
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<strong>Large</strong> <strong>Valve</strong><br />
<strong>Single</strong> <strong>Device</strong> <strong>Isolation</strong><br />
<strong>Problems</strong> & <strong>Solutions</strong>
What is <strong>Single</strong> <strong>Device</strong> <strong>Isolation</strong>?<br />
• Gates, stoplogs and valves are used to<br />
isolate a work area.<br />
• <strong>Single</strong> device isolation is the certification<br />
by a Professional Engineer that the device<br />
is safe to work behind.<br />
• In some jurisdictions certification is<br />
required in lieu of providing a double block<br />
and bleed isolation system.
What is required for SDI<br />
Certification?<br />
• Risk assessment.<br />
• Design review.<br />
• Condition assessment.<br />
• Maintenance review.<br />
• A written certification provided by a PE
What is KCBL experience with<br />
SDI?<br />
Gates <strong>Valve</strong>s Stoplogs<br />
52 28 19
Typical SDI <strong>Valve</strong> <strong>Problems</strong><br />
• Cracked Casting Hole Cover Plate Welds.<br />
• Leaking Seals – particularly metal to metal<br />
seals<br />
• Corroded Surfaces<br />
• Inadequate lockout schemes – blocking<br />
devices
Cover Plate Potential <strong>Problems</strong><br />
• Many older hydro plants have butterfly and<br />
spherical valves with cast steel rotors.<br />
• Castings for disks and plugs often included<br />
holes to allow the sand to be removed after<br />
casting.<br />
• The holes were plugged with welded plates.<br />
• Some of these welds may be cracked.<br />
• Worst case - the plate can fall out.
13 Ft. Dia. Butterfly <strong>Valve</strong>
5 Ft. Dia. Spherical <strong>Valve</strong>
Failed plug in a Spherical <strong>Valve</strong>
Typical Weld Detail
Typical Cracked Weld
Crack %<br />
% Cracked Welds vs. <strong>Valve</strong> Head<br />
Graph 1 - Crack % vs. Head on <strong>Valve</strong><br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
0 100 200 300 400<br />
Head (ft)
Crack %<br />
% Cracked Welds vs. <strong>Valve</strong> Dia.<br />
Graph 2 - Crack % vs. <strong>Valve</strong> Diameter<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
0 5 10 15<br />
<strong>Valve</strong> Disc Diameter (ft)
Crack %<br />
% Cracked Welds vs. <strong>Valve</strong> Age<br />
Graph 3 - Crack % vs <strong>Valve</strong> Age<br />
100<br />
80<br />
60<br />
40<br />
20<br />
0<br />
1920 1930 1940 1950 1960<br />
Year
Preliminary Observation<br />
• Cast valves built between 1928 and<br />
1960, with welded-in cover plates, may<br />
have cracks in more than 40% of the<br />
cover plate welds.
How Not To Fix The Crack!
How To Fix The Crack!
6 Ft. Dia. Butterfly After Repair
13 Ft. Dia. Butterfly <strong>Valve</strong>
13 Ft. Dia. Butterfly After Repair
Cover Plate Weld Conclusions<br />
• Cast valves may have cracked cover plate welds,<br />
• The cracks may result in the cover plates falling out,<br />
• Cracked welds pose a potential safety hazard to<br />
personnel working behind the closed valve,<br />
• The cracks can be detected relatively easily with<br />
magnetic particle NDT,<br />
• Partial repair of a cracked weld has been problematic,<br />
whereas complete replacement of the cover plate and<br />
new welding has proven to be completely successful.
Seal Upgrade<br />
• SDI failed twice on two 6 ft dia. butterfly<br />
valves due to excessive seal leakage
Original seal design
Redesigned Seal
New Seals Being Installed
New Seal After Installation
Leakage Through New Seals
Summary<br />
• Cast valves have issues, but they can<br />
often be solved at a fraction of the cost of<br />
a new valve<br />
• Casting hole cover plates can be replaced<br />
• New seals can be designed<br />
• Corrosion coatings can be renewed
The End (time to wake up!)<br />
Dan Campbell, P.Eng.<br />
Manager Hydro Projects<br />
Klohn Crippen Berger Ltd.<br />
500 - 2955 Virtual Way<br />
Vancouver, BC<br />
Canada, V5M 4X6<br />
Email: DCampbell@klohn.com