News/Blog
News/Blog
01, 1970
Valves are crucial components in every industrial system or process. Commercial valves are used to control the flow of media through pipelines, isolate specific sections of the conduit, and monitor the overall system reliability, among other functions. Due to these important roles, industrial valves must meet the highest standards of quality—they need to be leak-proof, reliable, functional, and durable.
In this article, we will explore carbon steel and forged steel valves, explaining how they are made, what sets them apart, and which is best suited for various applications. Continue reading to learn more.
Forged steel valves are created by a process known as "forging." Forging is developed based on heat energy to hard materials of steel, followed by the use of mechanical pressure to further convert the steel into a completed product. This method is used to create exceptionally robust and durable valves. Forged steel valves are ideal for high-temperature and high-pressure applications. However, only certain metals are suitable for the forging process. This technique is commonly used to create smaller, more specialized valves. For larger forged steel valves, manufacturing typically involves producing individual parts that are then welded or flanged together to form the complete valve.
Less Waste Production: Forged steel valves are made from solid metal sheets, which minimizes waste during manufacturing. Unlike casting, which requires more extensive reworking of the metal, forging generates significantly less waste.
Enhanced Durability and Longevity: The high pressure applied to the heated metal ensures that the finished product is free of internal holes or voids, and it reduces surface porosity. As a result, forged steel valves offer improved structural stability, ductility, and strength, making them more robust and long-lasting.
Reduced Thermal Stress: Forging produces steel valves with thinner walls, which leads to a reduced temperature differential. This allows the valve to reach thermal equilibrium more quickly, making it less susceptible to high-temperature wear. Forged steel valves are particularly reliable in power stations that frequently cycle between start-up and operational stages.
Improved Mechanical Properties: Forging creates mechanically strong components without the need for costly alloys. The alloy grain structure is optimized, ensuring a highly homogeneous composition and mechanical recrystallization, which enhances the valve’s mechanical properties.
High-Resistance Nozzle: Forged steel valves are capable of withstanding high pressures and stresses, offering exceptional durability. They are designed to endure extreme temperatures and high-pressure conditions without requiring adjustments, making them ideal for demanding applications.
Forging is a costly and energy-intensive process. The time and energy required for honing and polishing the finished product contribute to a longer production time, resulting in higher turnover rates for forged valves.
Additionally, forged steel valves have limitations in terms of the variety of forms and sizes that can be produced. They are typically preferred for manufacturing smaller valves and components, as larger valves must be made in sections, which can be expensive.
For larger valves, individual sections are forged and then welded or flanged together. This method increases the risk of leaks at the joints where the sections are connected.
Carbon steel valve is an iron alloy with carbon as the primary alloying element, and typically, no additional alloying components are added to alter its properties. It is commonly used in sand casting techniques to produce the frame and rotor of butterfly valves.
There are various grades of carbon steel, with cast categories like LCC (Low Carbon Content) and ASTM A216 WCB (Weldable Cast B-grade) being the most commonly used for valve frames and discs. WCB material is particularly suitable for high heat resistance, while LCC material is ideal for low (sub-zero) temperatures.
Cast carbon steel (ASTM A216, rating WCB) is often used for larger valves ranging from 1-1/2 to 24 inches. This material typically contains 30% carbon, 1% manganese, 0.05% phosphorus, 0.06% sulfur, and 0.06% silicon, offering the following properties:
- Tensile strength: 70,000 psi
- Yield strength: 36,000 psi
It is easily weldable and works well with steam, water, and gas. Carbon steel is known for its excellent mechanical properties, resistance to stress degradation and sulfides, as well as its ability to withstand various temperatures. It also provides exceptional toughness and wear resistance, making it suitable for use in gate, globe, and check valves at temperatures up to 454°C.
The main advantage of carbon steel is its cost-effectiveness. Carbon steel valves are an economical option in situations where features like corrosion resistance are less critical than price.
However, the primary disadvantage of carbon steel is its poor corrosion resistance. To mitigate this, surface coatings like paint can be applied, provided the mainline content does not erode the valve from within.
The forging process consists of several stages. First, the material, whether in the form of blocks, alloys, or billets, is chopped into smaller pieces. These parts are then annealed to a specific temperature, making the metal malleable and ductile. Once heated, hydraulic forces are used to shape the material into the desired form. Historically, this pressure was applied manually through power pounding, but today, automatic devices such as hydraulic presses are typically used.
After the metal has been shaped, it undergoes machining, refining, and thermal treatment to produce the final product. Depending on the temperature applied to the raw material, forging is categorized as follows:
Cold forging is performed at ambient temperatures with no additional heat applied to the material. Since the metal is less malleable than in warm or hot forging, more mechanical force is required to shape it.
In warm forging, the material is heated to temperatures ranging from 800 to 1000 degrees Celsius. At this stage, the metal becomes malleable, though not as pliable as in hot forging.
Hot forging occurs when the metal is heated to temperatures above 1000 degrees Fahrenheit (but less than 1300 degrees Fahrenheit). At these elevated temperatures, the material becomes extremely pliable, requiring only minimal pressure to form it into the desired shape.
Selecting the right valve for your project involves considering several factors. While forged valves are ideal for high-pressure, high-temperature applications, they come at a higher cost and can be challenging to standardize. On the other hand, carbon steel valves are more affordable and can be mass-produced in large quantities, though they may have potential structural gaps.
To make the best choice, it's advisable to consult with an expert valve manufacturer who can guide you in selecting the most suitable steel valve to meet the specific needs of your plant.
