Materials of discs and seats
Materials of discs and seats
(OP)
Dear all,
As far as I know ANSI B16.34 defines the allowable materials for body and cover but not for other like seats or discs. Are there alternative rules for those parts? What I usually do when specifying valves is to select those materials according to the type of body material (carbon steel, stainless etc) and design temperature, using ASME Sec. II Part D to get the allowable temperatures of each material.
Thankis
As far as I know ANSI B16.34 defines the allowable materials for body and cover but not for other like seats or discs. Are there alternative rules for those parts? What I usually do when specifying valves is to select those materials according to the type of body material (carbon steel, stainless etc) and design temperature, using ASME Sec. II Part D to get the allowable temperatures of each material.
Thankis





RE: Materials of discs and seats
RE: Materials of discs and seats
But, is there any code to say if a materail is allowable or not depending on the temperature of the service? (apart from other issues like corrosion, for example)
ANSI b16.34 as far as I know says nothing about those parts of the valves.
RE: Materials of discs and seats
Most valve companies have a table of compatibility of their valve seat materials with common environments and if you don’t see it ask. The rub come when you have a new process or process that is not covered in the tables. This is the time that one my require the assistance of a materials engineer to get you in the ballpark on the material selection or better yet recommendations for a specific combination of materials.
If you can get a standard seat material from a particular valve manufacturer that will work use it even though may be a little more costly than another valve with an adder. One always wants to stay away from specials unless it is absolutely necessary.
RE: Materials of discs and seats
You would use the relevant Code and other references to determine the suitability of the trim materials just as you would for the body material keeping one thing in mind: the trim materials have to be equal or better than the body material because they are "working" parts.
For example, let's say you are selecting the materials for a gate valve in a hydrocarbon process in a refinery. The governing code is ASME B31.3 and you would look at the Appendix to determine temperature limitations. If your piping is carbon steel then you would probably select the same valve body material knowing that the limits are -20 to 800 F. Next if you look at manufacturers catalogs (and API 600) you would see that SS 410 and SS 316 are the most common trims available. In this case we know that temperature limitations for these materials are higher so you are OK. By reviewing corrosion data you can verify whether these materials will be acceptable for your service (they probably are). Lastly, check out packing material. Graphite packing is standard and will work for a large range of services.