Stainless Steel Materials for Miniature Flow Control Valves
Stainless steel miniature flow control valves for demanding environments
Last updated on December 7th, 2019
This article is an excerpt from the new ISM technical resource: Stainless Steel and Miniature Flow Control Valves Guide from ISM
Industrial stainless steel piping and
Why stainless steel?
Stainless steel is a steel and so it is typically very strong. This gives it great pressure and temperature resistance. It is also a tougher, more durable metal than cast iron, ductile iron, brass or copper.
Stainless steels get their name from the fact that they are very corrosion resistant. This plus toughness and strength make them a preferred choice for compact miniature flow control valves. This is despite being a more expensive material.
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Why metal valves if plastic ones are frequently more corrosion resistant and more economical?
It’s true, plastic valves are more corrosion resistant than metal valves in most applications. But, metal valves are more durable and can resist both higher pressures and broader temperature ranges better than plastic valves.
Get more information about choosing between plastic, brass and stainless steel for valve bodies in our blog post: Miniature Ball Valves: Plastic, Brass or Stainless Steel?
Modular Check Valves
We've taken spring-loaded check valves to a whole new level. Mix and match imperial and metric connections. Watch the video.
The basic rules of thumb for stainless steel chemical resistance:
- Resistant to most acids
- Resistant to most weak bases
- Selectively resistant to organic solvents
Resistance to organics and organic solvents varies among stainless steels. It depends on the chemical, its concentration and the makeup of the stainless steel alloy.
Why you need to know more about stainless steels used in miniature and compact flow control valves
two-way ball valve
These full port and standard port ball valves have a great working temperature and pressure range. The body of the valves are CF8M stainless steel, but internal and external components are made of both CF8M and 304 stainless steels.
- CF8M stainless steel body, end cap, ball and stem stainless steel
- 304 stainless steel gland nut, spring washer, lever and lever nut
poppet check valve
These poppet check valves have a good working temperature and a great operating pressure range. The body and most of the components of these valves are 316 stainless steel but the retaining ring is 15-7 stainless steel.
- 316 stainless steel body, poppet retainer and spring
- 15-7 stainless steel retaining ring
What’s CF8M stainless steel? Why use both CF8M and 304 stainless steel in the same valve? Are CF8M and 304 equally corrosion resistant? What’s 15-7 stainless steel? If 316 stainless steel is so corrosion resistant, why use one part made of 15-7 when all the other metal used in the valve is 316?
Read on to find out more about the stainless steels used to make typical compact and miniature flow control valves.
The austenitic family of stainless steels are the most common stainless steel materials used to make miniature flow control valves.
Key elements added to austenitic stainless steel alloys or formulations
These elements work in combination to provide austenitic stainless steels with excellent corrosion resistance.
Why are austenitic stainless steels so popular for making miniature valves?
- Austenitic stainless steels are strong and durable
- Austenitic stainless steels are very corrosion resistant
- Austenitic stainless steels have broad operating temperature ranges
Typical austenitic stainless steels used in valves
These are the most common austenitic stainless steel types or alloys used to make compact and miniature flow control valves and valve components:
Typical valve components made of stainless steel
- Balls, poppets and pistons
- Retaining clips
- …and more
These check valve series are examples of stainless valves with bodies made of 303 stainless steel and internal assemblies or parts made of 304 stainless steel.
Using a 303 stainless steel makes small, intricate valve bodies easier and more economical to shape with high-speed automated machining. 304 stainless steels provide additional corrosion protection for the internal working parts of the valves.
A fairly typical high-quality stainless steel ball valve series that uses both 316 and 304 stainless steels:
316 stainless steel for the BVSS valve body and internal parts
These surfaces will be in contact with the gas or liquid (the media) flowing through the valve. 316 provides excellent corrosion resistance to aggressive gases and chemicals.
304 stainless steel for the BVSS external parts
These surfaces will not be in continuous contact with potentially aggressive chemicals. 303 parts are cheaper and easier to make and have good corrosion resistance.
Here is another fairly typical high-quality stainless steel ball valve series. This one uses 316 stainless steel for the body, ends and ball. It is offered in three different O-ring seal materials to provide the broadest range of chemical compatibility and corrosion resistance:
- Buna-N (nitrile rubber, NBR)
- EPDM (ethylene propylene)
- Viton® (fluoroelastomer)
316 vs 316L stainless steel
The main difference between 316 and 316L stainless steel is the difference in carbon content. 316 stainless steel has a maximum carbon content of about 0.08%. 316L has a maximum carbon content of about 0.03%. 316L also has lower percentages of other elements such as sulfur, phosphorus and copper. The 316L stainless steel is more ductile than 316 when annealed. It is also significantly more corrosion resistant, especially after being welded.
CF8M stainless steel
CF8M stainless steel is also called cast 316 stainless steel. Like the 316 type, CF8M stainless steel provides excellent corrosion resistance to aggressive gases and chemicals. 316 can only be worked by forging and machining. CF8M provides the option to start with a cast body. Cast valve bodies can be fairly intricate which reduces machining costs.
15-7 stainless steel
15-7 stainless steel has high strength and hardness plus good corrosion resistance. It is fairly easily to shape when this is done correctly. This stainless steel is particularly useful for applications that require high strength at high temperatures.
Keep these key takeaways in mind when buying a stainless steel miniature valve
Corrosion resistant does not mean invulnerable
Greater corrosion resistance does not mean invulnerable. You need to know the environment the valve will be installed in and what chemicals will be flowing it.
Keep in mind that mixtures of chemicals mean you cannot completely rely on published chemical compatibility reference information. Use chemical corrosion guides to make the best choices of valve materials for your application, get samples of the parts and test them in real conditions.
Get more information about material chemical compatibility and corrosion resistance in our article: How to Choose an In-line Filter – Chemical Compatibility
Corrosion resistant does not mean invulnerable
Stainless steel miniature valves are strong but they are still rated for specific temperature and pressure ranges. This is because elastomers and engineered plastics are frequently used for seals and sealing surfaces.
Stainless steel valves will be more expensive
Stainless steels are noticeably more expensive than brass and plastic. Part of the reason for this is because stainless steels are so tough. It takes more effort and special tooling to shape them. The results in stainless steel valves having significantly higher prices than brass and plastic valves.
Stainless steel valves are heavier
Does weight matter in your application? If so, remember that stainless steels are steel so they are heavy. Going with the right valve made of engineered plastic may give you the strength and temperature range you need without the added weight.
About the author
Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing (ISM), an ISO 9001-2015 supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world. He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM.