Ductile vs. Cast Iron Valves: What's the Difference?

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Customers from all kinds of industries need valves of all varieties for their high-demand processes. Valves are available in a huge number of materials for any application imaginable. A few of these materials are PVC, carbon steel, stainless steel, cast iron, and ductile iron. In this post we will focus on two of those materials: ductile iron and cast iron. The argument of "ductile vs. cast iron valves" has been going on for decades, as not everyone knows the differences.

Luckily, comparing valves made of ductile iron and cast iron is simple, as these materials have just a few major differences. We will outline properties of both materials and then go through the pros and cons of each. By the end of this blog post, you will be an iron expert!

Cast Iron Valves Specifications

Cast iron (also known as gray iron) is a type of metal that has been in use for hundreds of years. It is an alloy made from 96%-98% iron, 2%-4% carbon, and small amounts of silicone. It has impressive temperature tolerance, with some cast iron capable of handling temperatures over F (C). When it comes to pressure, cast iron's strength depends on its pressure class. The two most common are class 125 and class 250. At less extreme temperatures, class 125 cast iron flange is rated for pressures between 150 and 200 psi. Class 250 cast iron is a bit tougher, with pressure ratings from 300 to 500 psi. These pressures can vary by end type.

Cast iron is strong and will usually go undamaged even after going through intense vibrations. The main drawback of cast iron valves is that they are not very ductile at all. Virtually any bending will cause cast iron to crack and become useless. One great quality of cast iron is that it is not very expensive. As far as metals go, cast iron is usually the most economical option, which makes it a solid alternative for people on a budget.

Ductile Valves Specifications

The second material we're looking at is ductile iron. Ductile iron is a more modern iron alloy that is made with nodule-shaped graphite. This gives the material excellent ductility, so it will not necessarily break when bent. The temperature limit is a bit lower than cast iron, but it is still quite high at F (730C). When it comes to pressure, ductile iron valves also use pressure classes: 150 and 300. At standard outdoor temperatures, class 150 ductile iron keeps a seal up to 250 psi. Class 300 can stand up to pressures as high as 640 psi.

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Ductile iron has excellent corrosion resistance, tensile strength, and yield strength. Unlike cast iron, ductile iron does not break when it is bent, so it is more suited for high demand applications. Ductile iron is a strong and reliable material for pipes, fittings, and valves. One drawback is price. Ductile iron is typically more expensive than cast iron due to its more complicated chemical makeup. If your application requires a tougher material, however, you may need to spend a little more.

Ductile vs. Cast Iron Valves

Now that we've looked at both options individually, we will compare and contrast ductile and cast iron valves. Hopefully, this will help you decide which is best for you! We will compare these materials on durability, ease of installation, and price, so you can learn the most important details. For some more technical differences, check out this helpful article.

Durability

• Cast Iron: Cast iron is a strong material that can handle higher pressures than just about any plastic. When rated pressure of a cast iron valve or pipe is exceeded however, it can bend and crack. Cast iron has virtually zero ductility, meaning it is rigid and will crack if bent. Cast iron will also rust over time, so regular maintenance must be done to keep your valve clear of corrosion.
• Ductile Iron: Ductile iron also has impressive structural integrity. It can handle high pressures and temperatures without flinching. Thanks to its ductile nature,
  this material is also less likely to crack when bent. Ductile iron will also rust over time, but not as easily as cast iron.

Ease of Installation

• Cast Iron: This material gives the user many options when it comes to installation. Cast iron valves are typically bolted using flanges. Welding is difficult, but not impossible. Our cast iron valves are available with flanged ends, as this is a great method for high or low pressure applications.
• Ductile Iron: Ductile iron, because of its structural similarities to cast iron, gives the user many of the same installation options. Welding is not recommended,
  but bolting with the use of flanges is still the best option for most applications.

Price

• Cast Iron: Cast iron valves, due to their simpler manufacturing process, will save you a significant amount money compared to ductile iron valves. If you do not need the added benefits that ductile iron provides, cast iron is the smart move.
• Ductile Iron: Ductile iron is the more expensive option, but for good reason. It has properties that give it clear advantages over cast iron in many situations.

There you have it! Now you know that this is not an "ductile vs. cast iron valves" kind of issue. One is not always better than the other. It all depends on what you are using it for!

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