Why is Cast Steel Gate Valve Supplier Better?

The statement 'cast steel gate valve is a gate valve made of stainless steel' is inaccurate. It is only a one-sided understanding of the two types of valves from the literal meaning. In fact, there are still very big differences between the two. Cast steel gate valves refer to all gate valves made of metal steel materials that are cast into castings. Such

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gate valves are collectively referred to as cast steel gate valves. According to the material, it can also be divided into: carbon steel gate valve, stainless steel gate valve, low alloy steel gate valve (high temperature resistant chromium molybdenum steel belongs to this category), low temperature steel gate valve and so on. Corresponding to cast steel gate valves are also cast iron gate valves, forged steel gate valves, malleable cast iron gate valves.
I believe that at this time we can already see that the cast steel gate valve and the stainless steel gate valve are actually a molding method, that is, a process, and the other is a material type. Cast steel gate valves may be stainless steel gate valves, carbon steel gate valves, alloy steel gate valves. The stainless steel gate valve alone refers to the stainless steel valve, which can be cast or forged. In terms of scope: cast steel ' stainless steel valve.

Various cast steel gate valves correspond to different steel grades, which will be engraved on the valve body. The commonly used ones are as follows:
1. The grades of carbon steel gate valve castings are: WCA, WCB, WCC, LCB, etc.; applicable temperature is -46°C~425°C.
2. Stainless steel gate valve casting grades: 301 stainless steel, CF8 stainless steel (corresponding to forging 304 stainless steel), CF8M stainless steel (corresponding to forging 316 stainless steel), etc.; applicable temperature is -198 degrees ~ 816 degrees.

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3. Low-alloy steel is divided into high-temperature alloy steel and high-strength low-alloy steel, among which high-temperature alloy steel is often referred to as chromium-molybdenum steel. Casting grades of chromium molybdenum steel gate valve: ZG1Cr5Mo, ZG15Cr1MoV, ZG20CrMoV, WC6, WC9, C12A, etc. The applicable temperature is between 550 degrees and 750 degrees.

The applicable temperature for each specific grade of material is different, depending on the actual working conditions.
Another point worth mentioning here is that cast steel gate valves and forged steel gate valves are often confused because of their similar names, making it unclear how to choose. In fact, the direct way to distinguish is to look at the material grades. For example, 304 stainless steel castings are generally marked as CF3 or CF8, and forgings are generally marked as 06Cr19Ni10 or directly marked as 304. The choice of cast steel gate valve or forged steel gate valve is mainly determined by the working conditions. Forged steel gate valves are mainly used when the medium conditions are special. Because forged steel gate valves are more mature in technology, many domestic manufacturers can do it. It can also be a general reference from the caliber. Generally, forged gate valves below DN40 and cast gate valves above DN40, the pressure will be lower for larger calibers than for smaller calibers. But in the end, of course, we must actively consider the actual requirements of customers, and manufacturers can give some reasonable suggestions.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

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What is the safety valve setting? There are lots of steam systems running at 125#, but the safety valves lift at 150#. Very often, these systems are filled with 125# cast iron valves & strainers - because they're cheaper than cast steel. However, they don't meet code. Even if the safety valves lift at 125, unless the raised faces are removed from the flanges on the piping, they STILL don't meet code.

Check out for some shots of failed 125 cast iron components - usually involving fatalities.

I've worked with steam for 30 years, and I absolutely LOATHE 125 cast iron valves & fittings - even where permitted by code. So is it just a matter of pressure rating, or is there any other reason for choosing one over the other? In my case you're right, the PRV lifts at 130 psig. I was going to use a 250# or 300# valve anyway, which is why I asked which is better. Both are well above my relief valve setting. You are correct, for 125# steam it is a good idea to use either 250# cast iron or 300# steel. The main difference is that cast iron is much more brittle than steel.

So, if you drop a cast iron valve it may crack but not a steel.

My customers prefer also steel in steam service because of the chance of water hammer. Large banging in the pipes could crack the flange of cast iron and not steel.

In refineries and chemical plants they often do not allow cast iron, but for another reason. If there is a fire, the cast iron tensile strength breaks down at a lower temperature than that of steel.

Ductile Iron is more malleable than cast iron, has many of the same properties of steel at a reduced cost. It is a great material! I would agree that in general a gate valve is not the best for steam as it likely will erode on the bottom of the gate.

Gate valves do not throttle well like globes. However, gates do offer large Cv's for the size and if used for shut-off only and maintained full open for flowing they may be appropriate. However, do look at the design to assure the gate is out of the flow stream and talk to the manufacturer.

Further, regardless what you select the valve should be for steam service in addition to having the T & P capabilities.

Paul Ostand
The materials gray cast iron and later developed ductile cast iron have of course been mentioned on this thread (along with some references with regard to same). Gray cast iron is of course generally a quite venerable construction material that has been around for hundreds of years in piping, valves, and other applications.
However, while I don't think the particular all ductile iron valves pictured should be used for steam applications you may nevertheless be interested in the general material-related features and special testing of some gate valves contained in the four minutes or so video "Ductile versus Gray Presentation" near the bottom of the page under the heading 'Product Presentation Files'. This video provides some more information/clues as to how/why gray cast iron valves might be more easily overloaded or broken in handling, installation, and or service events than the much stronger/tougher ductile material, and probably also why some manufacturers and users have opted instead for ductile iron constructions. rconner:

That is a nice video.

BronYrAur:

One more bit of information. Jordan Valve makes a sliding gate valve specifically for steam service. It is available in DI, Steel and other materials. You might look at it for your application.
(I don't work there but I did at one time.)

Paul Ostand