valve body forgings production research and practice

The valve body forging production process seems simple but complex and variable; the application of valve products across all walks of life, there are many new materials, and new processes need time to practice repeatedly and research; there are also some new knowledge points that need to learn to explore, this paper only the author has experienced including nuclear power, military, LNG, hydrogenation, petrochemical field valve body forging production process practice for a general summary, including the valve background knowledge of the introduction, processing enterprise qualification requirements, valve materials, typical processes, equipment selection and the use of new technologies.

What is a valve?

The valve is a control part of the fluid system that can change the original direction of flow of the medium in the pipeline, the pressure of the medium, and the flow of the medium, which can achieve two directions to block or a single direction to block the flow of the medium.
There are many types of valves; the nominal size of the valves used in instrumentation control is as small as a few microns, while the largest nominal size of the valves used in industrial control pipelines reaches more than 10 meters. Valve operating pressure under specific conditions of use can be from a tiny 0.0013MPa to ultra-high pressure of 1000MPa, and the operating temperature range from ultra-low temperature -270 ℃ to ultra-high temperature of 1430 ℃.
Valve control methods are also varied; simple classification is manual, automatic, and semi-automatic. The way to achieve automatic and semi-automatic motor-driven reducer, hydraulic, pneumatic, etc., can be arranged in the pipeline sensor automatically collects pressure, fluid temperature, or other sensing signals through the control system, the actuator automatically or semi-automatic valve gate for lifting, sliding, swing or rotary movement, to change the size of its flow pipe area to achieve its control function.

Classification of valves

(1) According to classification, the valve can be divided into.

• 1) Shut-off class, standing in the cold, heat or machinery and equipment at the import or export, including gate valves, globe valves, plug valves, ball valves, butterfly valves, needle valves, diaphragm valves, etc., the role is to block the flow of fluid media in the pipeline.
• 2) the pre-command pipeline flow can adjust the regulation class, including an automatic or manual adjustment.
• 3) Protection class, mainly used to limit the rated pressure in the pipeline, also called safety valves, such as ADS system automatic pressure relief valve (Figure 1), are automatically open the way.
• 4) Special category refers to the unique design requirements of the pipeline and the manufacture of valves, such as installed at the lowest drain valve, installed at the highest point or transmission pipeline inflection point exhaust valve, etc.

(2) According to the main parameters, the valves can be divided into vacuum, low-pressure, medium, high-pressure, ultra-high, and filters according to the different pressure ranges. According to the different working temperatures, the valve can be divided into an ultra-low temperature valve, room temperature valve, medium temperature valve, and high temperature valve (Figure 2).
(3) According to the drive mode, the valve can be divided into automatic, power-driven (Figure 3), and manual valves.
(4) By the nominal size of the division, according to the size of the valve diameter size specifications, the valve can be divided into small diameter valves, medium diameter valves, large diameter valves (Figure 4), and extra large diameter valves.
(5) According to the structural characteristics of the division, according to the closure in the seat of the trajectory of movement, the valve has a truncated door-shaped, plug-shaped, gate shaped, swing-shaped (Figure 5), butterfly-shaped, slide valve-shaped, orbital-spherical, etc.
(6) According to the connection method, the valve in the pipeline connection method can be divided into threaded connection valve, flange connection valve, welding connection valve, clamp connection valve, ferrule connection valve, and butt connection valve.
(7) According to the material division, the valve can be divided into metal material valves and non-metallic material valves.
The main parts of the valve (such as valve body, cover, gate, stuffing box, packing gland, stem, etc.) using forging technology, increasing the proportion of the valve, especially the special working conditions of the valve more and more stringent quality requirements, the material is more and more complex, so the forging industry has brought market opportunities, but also technical challenges.

Analysis of the market demand for forged steel valves

At present, the domestic energy, chemical, pharmaceutical, and other fields of environmental protection strengthen and upgrade the need to accelerate the production of certain special needs of the valve; now, most of the valve products can be manufactured in the domestic.
(1) Nuclear power valves, from the original 100% imported to more than 80% of the current localization, including the main steam isolation valve, safety valves, and special conditions under the development of fast closing valve success. Especially since 2014, China’s nuclear power plants have completely independent intellectual property rights of the Hualong One; the valve localization rate is higher, including the core technology of the CAP1400 nuclear level burst valve, its scientific research is more difficult, our company participated in the whole study, and manufactured its core forgings, the formation of a set of standardized standards, including “stainless steel valve body forging technology the company has formed a set of standardized standards, including “Stainless Steel Valve Forging Technology,” “CAP1400 Nuclear Grade Pump Valve Forgings Raw Material Technology”, “CAP1400 Forging Technology”, “CAP1400 Forging Heating Technology”, “CAP1400 Nuclear Grade Pump Valve Forgings Heat Treatment Technology“, “CAP1400 Nuclear Grade Pump Valve Forgings Inspection Technology Requirements”, etc. More than 10 national and industry standards.

Figure.1 ADS system automatic pressure relief valve

Figure.2 High temperature and high-pressure self-pressure sealing shut-off valve

Figure.3 Electric three-way shut-off valve for nuclear level 2

Figure.4 Nuclear class I large-diameter angular bellows shut-off check valve.

Figure.5 Self-pressure sealing swing check valve
(2) Hydrogenation device valve, mainly used in liquid hydrogen storage equipment, is used in -196 ℃ low-temperature conditions; corrosion resistance, creep resistance, safety, no leakage, reliability, and stability is the first requirement.
(3) LNG valve, recently the country is gradually eliminating gas, replacing natural gas, to transport, storage is more convenient. Usually, the gas is transformed into a liquid, and the valve use conditions are also low temperature.
(4) thermal power units of ultra-supercritical valves, used in high-temperature conditions, the working conditions are also relatively harsh.

The current status of domestic development of valves

In recent years, research institutes, universities, professional institutions, and manufacturing plants engaged in valve research on the valve for detailed, thorough research and test verification. China’s low-end valves already have an absolute right to speak in the world, under the leadership of the national policy on technology research, and actively research and development of high-end valves research, and has made great progress; most products have been comparable to similar products of international enterprises, the emergence of several industry-leading enterprises. At present, in the LNG, hydrogenation, thermal power generation, nuclear infrastructure industry, aviation, and aerospace field using high-end valves have domestic products; in actual use, its stability and reliability performance is still good, recognized by industry enterprises, such as integral forging nuclear-grade wedge gate valve (Figure 6), nuclear-grade swing check valve (Figure 7). The valve industry has entered an era of innovation and innovation and development of the key period, followed by some new national standards, industry standards, and group standards that also need to be updated, which requires the active participation of relevant units. For example, our company is the main participant in drafting the “industrial valves with stainless steel forgings technical conditions” (standard number: GB/T 35741-2017), which has been promulgated.

Technical level

China’s mechanical and electrical products are in a pivotal international position; with the popularity of products in the world, competition has never been fiercer, the valve products are no exception, and the long international history of big-name enterprises must face each other in the high-end products, we still lack experience and theoretical support, stability still needs to go through the test, the whole industry needs to work together.
After decades of efforts, the domestic production of valves can now basically meet the needs of industrial development; its complete set of matching rates and technical indicators have been significantly improved. In recent years, although China’s valve industry has emerged from the annual output value of billions of large enterprises, but is still dominated by small and medium-sized enterprises; its management capacity and management level, technology research and development, and testing still need a breakthrough. Supporting the valve class forgings production enterprises also need to be in enterprise management, quality control, reduced production costs, on-time delivery, and other aspects of the full effort.
In the next few years and a long time, China’s petrochemical, natural gas, metallurgy, electric power, urban construction, and other industries will continue to increase demand for valves. Therefore, the production of valves will have good prospects.

Figure.6 Integral forged nuclear-grade wedge gate valve

Figure.7 Nuclear-grade swing check valve

The importance of valve quality

In July 2014, a small valve failure on a tanker truck caused a leak; the tanker truck flowed a hundred meters “gasoline river.” Small valves can cause such losses; for large valves, once the failure, the loss is unimaginable, so the valve, regardless of size, pays close attention to quality.
China’s rapid development of nuclear power has entered the third-generation technology stage, and the valve’s importance is increasingly obvious. Almost every system has a valve, a 1 million kilowatt unit, and about 15,000 valves. However, the investment accounted for only about 2% of the nuclear power plant, but the annual maintenance costs accounted for about 50% of the nuclear power plant.
Once the valve fails, the consequences are unimaginable; the key circuit of the valve as far as possible using a forged steel structure. The quality of forgings is critical. It must meet the procurement of technical conditions and related standards, as the production of supporting enterprises must do their homework in advance in quality assurance, resource allocation, production management, and other aspects.

Valve forgings production enterprise qualification requirements

According to the different uses of valves, valve owners have strict requirements for the qualification of suppliers. For example, nuclear power is the rapid development of the industry in recent years, localization is also a matter of recent years, its profit return is relatively high, if the production of forging blanks for its supporting, must have the production qualifications and services approved by the National Nuclear Safety Administration audit, each year to accept from the national authorities, engineering companies, owners and other audit bodies for many regular and irregular quality assurance monitoring; production enterprises The relevant personnel qualifications (such as nondestructive testing, welding, inspection personnel) must also meet the requirements, all need to obtain a certificate of qualification; at the same time cannot exceed the scope of design, manufacturing and supply covered by the certificate, the civil nuclear power production qualification of enterprises, but also to obtain the military nuclear power production qualification, before the production of military nuclear power products. With the qualification certificate of ASMENPT, they can supply AP1000 and other projects.
Foreign large valve procurement enterprises also require suppliers to obtain the corresponding supplier qualification certificates, such as CE certification, EMERSON, BP two-party certificate, etc. Military products also require suppliers with military management system qualification certificates, confidentiality certificates, and second-party audit certifications.
In short, technically feasible does not prove that you can do the valve, tee series products; you must understand whether you need to obtain the second party or third-party certification permission.

Typical materials of valve body forgings

Our company has forged and produced the following materials:

• (1) Carbon steel series: 20Mn, A105, LF2, A42AP, P355NH, P280GH;
• (2) Alloy structural steel series: F5, F11, 1Cr5Mo, 12Cr1MoV, 30CrMo, 4130, 18CrNiMo7-6, 34CrNiMo6;
• (3) Stainless steel series: 1Cr13, 2Cr13, F316, F316L, F304, F304L, F321, F347, F310, Z2CND18-12NS, Z2CN19-10, 17-4;
• (4) Nickel-based alloys: 660, 630, 690, 625, Hastelloy, Inconel materials, Monel alloys;
• (5) Copper alloys;
• (6) Titanium alloys.

We must continue exploring and practicing material changes derived from the new forging process and experience methods.

Typical valve body forging process introduction (body, cover)

Overall forging of the flange valve body

Flange and valve body forging have been the development direction in recent years; the advantage of this is to avoid welding defects and enhance valve reliability completely; the disadvantage is that the forging difficulty increases, the material utilization rate decreases, and this form of structure will gradually be promoted to replace the welding structure, how to further optimize the forging process is the responsibility and obligation of forging colleagues.
(1) Forging process is as follows: raw material inspection → feeding → heating → flattening → pre-forging → final forging → edge cutting → heat treatment → surface cleaning → non-destructive inspection → rustproof → packaging → delivery.

(2) Basic information on forging parts. External dimensions of forging blank for double flange valve body: maximum diameter at flange 125mm, the total length of the valve body 164mm, as shown in Figure 8.

Figure.8 Double flange valve body forging blank
1) Blank making. The raw material used 110mm diameter, 140mm length of F316 stainless steel round bar material. The round bar stock is flattened directly on the die plane to 70mm, as shown in Figure 9.
2) Pre-forging. Pre-forging shape flange diameter of 125.86mm at both ends, flange cross-sectional area of 12435mm², and the length between the two ends of the flange is 165mm. Billet, the material is 70mm high, 140mm wide, 160mm long, and has a cross-sectional area of about 9800 mm². Billet shape and pre-forging shape comparison: the cross-sectional area is smaller than pre-forging; the length is smaller than pre-forging. The flattened material is placed directly in the pre-forged cavity (Figure 10). The material was not upsetting the middle flange part separately during the billet-making process.

Figure.9 Blanking
3) Final forging. The pre-forged blank is placed in the final forging die and directly final forged (Figure 11).

Fig.10 Pre-forging

Figure.11 Final forging
4) Edge cutting. After final forging, the blank is put into the edge cutting die, the flying edge is removed, and the forging is opened into the final shape (Figure 12).

Supercritical valve body forging

Mainly used in thermal power projects, small forgings are not distinguished from the conventional forging process, basically the same, so they will not be introduced. For large forgings weighing several tons, our forging process is as follows:

• (1) Must ensure the correctness of the heating process and adequate and appropriate forging ratio because we re-heat, the grain will recrystallize and grow through the forging process of external forces on the grain refinement, the forging process of heating temperature, holding time, the heating rate must be strictly controlled to avoid internal cracking; the cooling process is also particularly critical, alloy steel needs slow cooling, can take pit cooling, cooling with the furnace The cooling process is also particularly critical, the alloy steel needs slow cooling, can take pit cooling, cooling with the furnace, control cooling, etc., with the conditions of the enterprise, it is recommended that the forging directly after the furnace through a given program to control the cooling rate.
• (2) 10-inch valve body forging process route. Material entry inspection → material → heating → pre-forging billet → mold forming → out of the mold.
• (3) The basic information of the valve body. 10-inch valve body forming forgings, the total mass of forgings is 1270kg; the die assembly diagram and forming parts are shown in Figure 13.

Figure.12 Cutting edge

Figure.13 Assembly diagram of die and forming part

Forging of CAP1400 blast valve

This is the “Liaoning Science and Technology Innovation Major Special Project” project undertaken by our company; forging is important. Currently, CAP1400 is a worldwide innovative product, AP1000 is a foreign advanced technology introduced by China, and the successful independent research and development of CAP1400 is a milestone product that will be used in Hualong-1.
Blast valve body forging process route for material admission inspection → under the material → heating → pre-forging billet → tire die buckling type → punching shaping. Blast valve body forging and forging process simulation are shown in Figure 14.

Figure.14 Blast valve body forging and forging process simulation

Ball valve body casting to forging

From the point of view of product performance, forging is superior to casting. Still, the process requires us to continue improving to compensate for the lack of material utilization. Figure 15 ball valve body forgings are the casting parts with forgings to replace, is a future direction, need to forge colleagues to improve technology to create their market areas.

LNG valve body, valve cover forging

LNG valve class forgings, mainly stainless steel forgings, to prevent the subsequent process product quality defects, we try using a composite die; in practice, to produce good results, the scrap rate has been effectively curbed, and the level of conventional product quality is the same. The composite die-cutting and punching design reduces the production workstation and solves the problem of forging punching; cutting edge deformation needs to be bigger. The sketch of the composite die is shown in Figure 16.

Figure.15 Ball valve body forgings

Forging of nuclear grade valve body forgings

Nuclear-grade valve body forging requires companies to obtain the appropriate qualifications; practitioners must be filed, operating procedures must be approved and filed in advance, and the whole process with traceability. Material suppliers to be in the range of qualified suppliers; inspection tests may not cross the point (E, R, H point). NDT personnel must be filed with the Nuclear Safety Authority and must not exceed the scope of testing. The acquisition of specimens and technical documents must be strictly consistent, etc. The forgings are shown in Figure 17.

Figure.16 Sketch of composite die

Figure.17 Nuclear-grade valve body forgings

Forging equipment selection and its advantages and disadvantages comparison

Hot die-forging mechanical presses

For valve body forgings and mass production, we usually consider the equipment is hot-die forging mechanical press; the production process is easy to control, has high efficiency, has excellent dimensional accuracy, and has moderate manufacturing costs. We can select the equipment that should be used according to the theoretical formula calculation or practical experience, which is the basic theoretical knowledge that ordinary technicians can master. The production environment is clean and environmentally friendly, the labor conditions are good, and it is easy to realize automatic production.

Electric screw presses

Compared with friction presses, they have greater product advantages and are being popularized and used at home and abroad, and tend to replace hot-die forging mechanical presses; after all, the one-time investment cost is lower, and the product quality and production efficiency are more satisfactory, and they can also be controlled automatically. The forging process is produced using robotic operations.

Die forging hammer

Simple valve body forgings can choose to use such equipment because there is no ejector device, the product is out of the die angle, size is not good control, cavity layout is difficult, and precision forgings are difficult to ensure the accuracy of more restrictions.

Multi-directional forging presses

A multi-directional die forging press should be the most appropriate choice of equipment for valve body products and tee products; the highest material utilization rate and precious metals would be more appropriate; improving production efficiency still needs further exploration. After improving efficiency, it has a wide range of market prospects. In the future, valve body forging attainment should be great in the tee field.

Tire die forging

This process can be selected appropriately for valve body forgings with small batch sizes, simple shapes, and large single weights. The die is simple; the investment is not large; it can save material than free forging; the process is not complicated; the forging is larger and can save raw materials and machining costs; the metal flow line is also closer to the product shape, more reliable performance, higher life. The product performance test bar can be taken from the product master, and the production efficiency is much higher than free forging.

Friction presses

If the batch is small, choosing this type of equipment is recommended. Because from the equipment comparison, the efficiency is lower than that of a hot die forging press, but the equipment investment is lower, and the biggest advantage is that it can produce products with larger stroke requirements, with upper and lower ejector devices.

Hydraulic presses

The hydraulic press is a universal machine. The disadvantage is also prominent: the efficiency is the lowest. The advantage is that it can be used to solve problems that other equipment cannot solve.

For hammering

Using less and less is not recommended to choose this type of equipment to produce valve-type forgings.

Conclusion

Forged steel valves in the industrial field have gradually been enhanced, and the development prospects are broad; with the further localization of major key equipment and the gradual expansion of the export market, the demand for valve body forgings is also steadily increasing; we have more than 40 years to explore the process of valve body forgings, participated in the development of several national science and technology innovation major special products, the completion of several national and industry standards, several forged steel valve products have passed the national appraisal, and more than twenty invention patents. But the high-temperature resistance and high alloy of high-strength materials forging process requires further in-depth research; while there is still much work to be done on how to improve the material utilization rate further, I hope that our forging industry experts and operators work together to do the best valve body forgings.
Author: Ji Changquan, Wang He