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

[massiveT]

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.

 

[metengr]

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.

 

[NickelMet]

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