Microbes Attack Water Pipe
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THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS |
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The Catawba Nuclear Station in York County, South Carolina. |
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DUPLEX STAINLESS STEEL water service piping at the Catawba Nuclear Station. |
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WATER FROM LAKE WYLIE in South Carolina is rich in nutrients,therefore
microbiologically influenced corrosion developed in the service water piping at the Catawba Nuclear
Station. This piping is now being replaced with duplex stainless steel. |
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U.S. nuclear power plants replace carbon steel water service pipes with duplex pipe by Carroll
McCormick
Nickel Magazine, December 2006 --Several nuclear power plants built in the United States in the 1970s and ’80s are now replacing their water service piping with nickel-containing stainless steel pipe for longer life and corrosion resistance.
The Catawba Nuclear Station in York County, South Carolina, for example, is replacing original carbon steel cooling water piping with duplex stainless steel S32205. The plant, operated by Duke Energy, was commissioned in 1985 and has a rated output of 2,258 megawatts.
To date, Catawba has replaced 152 metres of 914- and 610-millimetre (mm) outside diameter pipe with a 9.53-mmm wall thickness. “We’re looking at replacing all the service water piping,” says Curtiss Blackwelder, senior technical specialist at the plant.
The original carbon steel piping (mostly API 5L Grade B) has suffered from general corrosion and microbiologically influenced corrosion (MIC). “The MIC is generally reserved to the welds, but we’ve also seen preferential weld attacks due to corrosion,” says Blackwelder.
Catawba is a fresh-water plant, and carbon steel was the material of choice when it was designed in the 1970s. But as it turns out, the water supply from Lake Wylie is rich in nutrients, which proved beneficial for the development of MIC, says Steve Lefler, principle engineer at the Duke Energy’s Catawba nuclear station. “Water chemistry is a moving target,” he notes, adding, “It seems like a prudent decision to use materials that afford the greater protection.”
Catawba performed visual inspections on the replacement piping last year. “It looks like new,” says Lefler. “It’s as thick as the day we bought it and there have been no MIC attacks.”
The approval in November 2005 of Code Case N-741 for ASME Section III Boiler and Pressure Vessel Code for the use of duplex stainless steel S32205 for ASME Section III Code water piping opens the door to its eventual approval in the United States by the Nuclear Regulatory Commission (NRC).
“This is an important step for us, though until this Code Case is reviewed and approved by the NRC, we’ll have to submit a relief request to the Commission to use it,” Lefler says.
Further replacement of carbon steel service water piping at the Catawba plant is likely.
In addition to being resistant to corrosion and MIC attack, S32205 is a good choice for Catawba ASME Section III Code piping because the alloy is already in the ASME B31.1 Power Piping Design & Fabrication Code. It’s readily available commercially and easy to construct, weld and put together, according to Blackwelder.
“Before this Code Case was completed, we were severely limited as to where we could use duplex,” notes Lefler. “This was a good development for our industry: it gives us the opportunity to use this material in applications where we couldn’t use it before.”
PHOTOS: Duke Energy
Rita Sipe |
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