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Replacing some old 5Cr Valves with 2-1/4Cr

Replacing some old 5Cr Valves with 2-1/4Cr

Replacing some old 5Cr Valves with 2-1/4Cr

(OP)
We are replacing some old 5Cr Gate Valves.  Operations has requested Ball Valves since they are easier to operate.  The only ball valve I can find that meets all of our requirements is only availabe in 2-1/4Cr.  The 2-1/4Cr material (A217-WC9) has higher allowable stresses than 5Cr (A217-C5) at the same temperatures so I think it should be fine.  

Does any one know if there are any issues with putting the 2-1/4Cr valve into the existing 5Cr piping?  

The connections are flanged so welding is not an issue.

RE: Replacing some old 5Cr Valves with 2-1/4Cr

Yes. If you have a concern with steam flashing in drains off of HP feedwater heaters or on HP/IP steam turbine extraction lines, the 5% Cr alloy valve would be the preferred choice because of increased resistance to steam erosion. Using the 2.25% Cr – 1% Mo alloy valve may result in steam erosion problems to the valve body.

RE: Replacing some old 5Cr Valves with 2-1/4Cr

What kind of stream is passing through the valve?  (Composition, temperature, pressure...)

The 2¼-Cr steel in some cases will not be a good choice.  One of which is alluded to by metengr.  Another case would be sulfidation corrosion.

~NiM

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