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steam safety valve seat and nozzle material

steam safety valve seat and nozzle material

steam safety valve seat and nozzle material

(OP)
I'm working in a steam power plant, one of our usual problems are the corrosion of the safety relief valves of the steam line, who has the temp. of 550 degree centigrade and around 10 MPa of steam, as you know the valves are expensive and some times it needs the shutdown of the turbine for change or repair of the valve.
I was searching about the materials with high corrosion Resistance, and wear resistance, i found that Tungsten Carbide can have a very good specifications for this usage.
I found that this material is abit brittle,
have anyone used this material in a seat or nozzle of a valve before?
any other suggestions?
notice that the current alloys in our valves are a type of Inconel that claims to be wear and corrosion resistance, but in this working condition in doesn't suffer for more than afew monthes of working!

RE: steam safety valve seat and nozzle material


Mortezaerospace,

Tungsten carbide is quite commonly used for high-temperature valves in Europe/world-wide, most often as a layer on top of other materials. Used is for instance (alone or with layer) the EN 4571 / AISI 316 Ti (stainless steel with an amount of titan for better workability). I have no (little) experience directly with 550 deg C and 10MPa steam. If you search for European valves you could probably get more information directly from local suppliers.

RE: steam safety valve seat and nozzle material

Hi Mortezaerospace,

For this kind of application, normally we use AISI 321 as trim base material, with Stellite overlay.
Stellite 6 indeed is at the temperature threshold. Therefore suggest to use either Stellite 20 and or Stellite 21 to achieve hardness level as per your requirement.
There is a debate though that Stellite can suffer SCC from Steam with Amine containment. And also Inconel 750 may exhibit SCC.

Your failure mode is not really clear though.
Wear --> do you deliberately let the Relief valve popped up frequently by setting it near the Operating pressure?? I personally think most material will suffer wear if kept in this condition.

Regards,
MR

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

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