EDF Energy

Ultra-Hard Tungsten Carbide Based Coatings
EDF Energy
Case Study
 Profile
EDF Energy is one of the UK’s largest energy companies and the largest
producer of low-carbon electricity. A wholly-owned subsidiary of EDF Group,
one of Europe's largest energy groups, EDF Energy generates around one fifth
of the UK's electricity and employs around 15,000 people.
The Nuclear Generation business unit provides the UK with 20% of its power.
EDF Energy owns and operates eight nuclear power stations with a combined
capacity of almost 9,000 megawatts.
Hinkley Point B nuclear power station in Somerset has two advanced gascooled reactors (AGR) and was commissioned in 1976. It has two 660 MW
turbo alternator sets and is capable of supplying electricity for more than 1.5
million homes.
The coating’s ability to
easily coat internal
surfaces evenly, its
performance in testing
and the ease of
implementation and
maintenance made
 Challenge
With many more years of operation planned for Hinkley Point B, the station
continues to invest in the plant and materials to ensure that efficiency, reliability
and safety is maintained or improved further where possible.
Hardide the solution of
choice for EDF Energy.
Each of the boiler feed pump turbines are controlled by a pair of governor
valves on a common steam chest. The two valves control the steam entering
the 15MW turbines. These are modulated to control the feed flow and maintain
the 160 bar boiler pressure.
Excessive wear degradation to the boiler feed pump governor valve covers was
affecting reliability of the units between major overhauls. This was due to the
station increasing the operational range of the main turbine generators.
Increased throttling of valves for lower turbine loads resulted in larger forces
being transmitted to the valve components.
Removal of the valve covers revealed wear rings where the harder piston rings
had fretted into the bore. The bore has a traditional coating of stellite 6 and the
piston rings a harder cobalt alloy.
 Further information
Robin Gillham
Business Development
Manager
M: +44 (0) 7949 292719
E: [email protected]
W: www.hardide.com
Hardide Coatings Limited, 11 Wedgwood Road, Bicester, OX26 4UL, United Kingdom
Tel: +44 (0) 1869 353830 Fax: +44 (0) 1869 353831 www.hardide.com
Ultra-Hard Tungsten Carbide Based Coatings
 Solution
Hardide’s principle hardface coating was identified as the most appropriate
solution to extend the life of the boiler feed steam valves. It is cost effective and
provides a tribological improvement to the original design.
The Hardide-T coating was employed to reduce the piston ring and bore friction
coefficient. The only material change was in the valve piston sleeve liner to
reduce system wear from abrasion, adhesion and fretting. This would transfer
wear to the piston rings which are easily exchanged during planned overhaul
outage.
Hardide T has hardness of 1100 to 1600 Hv and typical coating thickness of 50
microns. The low temperature CVD, being both binder and cobalt-free meant it
could potentially be irradiated without producing highly radioactive and
hazardous Co60 isotopes. The coating had suitable toughness, crack and
impact resistance and surface finish.
The low temperature CVD Tungsten Carbide nano-particles (1-2 nano-meters)
were dispersed in a tungsten matrix. The Hardide coating was particularly
attractive because it could be deployed in a 50 micron layer which was
accommodated by the existing piston ring tolerances.
Graham Young, steam & rotating plant engineer at EDF Energy, said: “The
benefits of this option were the reduced risk compared to alternative options
and simplicity of the engineering change as it is based on the existing
equipment pedigree. We could utilise the existing valve equipment with an aim
to merely improve the wear characteristics. Implementation would also be
straightforward as piston rings could be changed at scheduled outage.
“The coating also eliminated the need for post machining and changing of the
piston ring dimensions. Hardide provided excellent troubleshooting support to
the technical challenges in applying the coating process. Hardide also delivered
the parts in time so as not to affect the availability of the power plant
equipment.”
The coating’s ability to easily coat internal surfaces evenly, its performance in
testing and the ease of implementation and maintenance made Hardide the
solution of choice for EDF Energy. It enabled the company to continue to use
the existing equipment which would be very expensive to replace, as well as
require validation and safety case development, and will allow EDF Energy to
operate smoothly between planned outages.
The valves have now been operating for two years with no identified operational
issues. The coating will be fully validated for longer term operation when the
pump is opened up for maintenance in 2014.
Hardide Coatings Limited, 11 Wedgwood Road, Bicester, OX26 4UL, United Kingdom
Tel: +44 (0) 1869 353830 Fax: +44 (0) 1869 353831 www.hardide.com
 Further information
Robin Gillham
Business Development
Manager
M: +44 (0) 7949 292719
E: [email protected]
W: www.hardide.com

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