Study on technology of large diameter tube sheet forging

For the large diameter and thin thickness of large tube plate forgings, the deformation mechanism and process were studied and analyzed. By reasonably selecting the process parameters, improving the forging process, and proposing new operation and measurement methods, we completed the production trial production of large tube plate forgings with a diameter of 5825mm, and verified the reasonableness of the new forging process design.

Pressure vessel with a large diameter and thin plate forgings, the shape is relatively simple, usually due to flaw detection found dense inclusions defects and bottom wave reduction does not meet national standards and scrap [1]. Yaang production of φ5825mm large pipe plate forgings is the largest forgings since the establishment of the plant, many aspects have encountered great challenges. To solve this problem, the technical staff through continuous innovation, exploration, design a new forging process, operation methods and measurement methods, and finally completed the production of plate forgings trial production.

1. Analysis of traditional forging process

At present, Yaang production of large pipe plate forgings, usually using the following two process options:

• (1) The diameter of the pipe plate direct spin forming is small, using ingot upsetting → drawing length under the material → billet pre-forging → spin forming, roll forging outer circle combined with the forming method.
• (2) The tube plate forging into a square plate after welding forming larger diameter, using ingot upsetting → wide anvil flattening (square plate) → flattening on all sides, out of the finished product → flame gas cutting → riveting welding forming process. These two tube plate forging process is more mature, the forging process parameters control is also more reasonable, so the internal quality is better, to meet the delivery requirements.

The diameter of the tube sheet forging reaches 5825mm, which exceeds the forging capacity of the company’s hydraulic press equipment, so the program (1) cannot meet the requirements; if the program (2) is directly forged into a square plate, the forging quality is too large, beyond the customer’s cost capacity, and the program (2) is not feasible. Therefore, it is necessary to innovate the forging process and adopt a new forming method that can guarantee the internal quality of the tube sheet and reduce the cost of the customer.

2. New forming process research

2.1 Forging shape determination

From the analysis, it can be seen that the above two traditional processes can not meet the manufacturing requirements of this specification pipe plate. After careful analysis and research, we decided to take 1/2 circle forming, the shape of half-round tube plate forging is similar to half hexagon, which reduces the quality of forgings and meets the customer’s requirements for weight reduction of forgings, but increases the difficulty of operation and makes the finished product more difficult. Figure 1 shows a schematic diagram of the semi-circular plate forging.

Figure.1 Semi-circular plate forgings

2.2 Forging inspection method

Forging inspection is an important link to ensure the final size of the product, a reasonable and practical inspection method, not only to determine the size of each part of the product, but also to ensure the accuracy and efficiency of the measurement. The large tube and plate forgings are mainly formed partially at high temperature and produced in an overall controlled way, and in the finished product process, the shape of the forging is nearly semi-circular to ensure the corner dimensions of both ends. Obviously, there are great limitations in using general measurement tools to determine the dimensions of each part of the component, so it is especially important to explore new measurement methods. Based on this, considering the finished dimensions of the tube plate forgings, it was decided to make a semi-circular sample, and the dimensions of each part of the final forgings were easily determined by comparison, as shown in Figure 2.

Figure.2 Inspection tool

2.3 Analysis of main deformation stage

Due to the large diameter and thin thickness of the tube plate, it is difficult to achieve the dimensional requirements in the main deformation stage after adopting WHF method to draw the square directly; and it is necessary to ensure the internal quality of the forging as well as the forging penetration of the ingot core. Based on these two considerations, the forging process is determined to adopt the wide anvil drawing, large anvil feed and large press down amount, with the press down amount of 20%. When the width exceeds the size of the hammer head, the lower anvil is replaced by a platform for flattening, and the anvil feed and press down amounts are small, while the edges should be chamfered. In the process of finished product, we must ensure the size of forging width and length direction, and make sure that the material is evenly divided in each part to avoid the lack of material in the middle part when the angles are poured out at both ends, which leads to the dimensional difference.

2.4 Design of metallurgical auxiliary tools

Usually, general metallurgical auxiliaries and rolling anvils are used for tube and plate forgings to completely ensure forging and forming. In view of the large size of this batch of pipe plate and the special forming process, the existing 8400T hydraulic press metallurgical auxiliary tools are small and not suitable for forging this size of pipe plate, so we modified the metallurgical auxiliary tools ourselves and widened the original specifications of wide anvil and narrow anvil by welding the remaining blocks.

3. New process of tube forging

In order to ensure the size and internal quality of the forging, the following process was determined through research and analysis: ingot upsetting → WHF method of wide anvil squared and flattened → flattened on all sides → chamfering of the edges while flattening → trimming to process size [2].

• (1) The biggest highlight of this process solution is the wide anvil strong pressure flattening and partial forming of the billet. Wide anvil large amount of pressure under the method of a large amount of deformation, when a certain deformation volume, the hole surface contact, through the role of recrystallization and diffusion can be completely welded internal defects; billet local forming can ensure the internal quality of forgings, effectively avoid dense flake inclusions defects, by the law of least resistance know, local forming the metal matrix to local overall flow, so that the core of the pressed part is subjected to higher hydrostatic pressure, The tendency of inclusions to become flaky is greatly reduced [3].
• (2) The process of forging and forming the most difficult operational difficulties, the size is difficult to ensure. When the wide anvil is flattened, the size of the width direction must be ensured, and when the flattening and squared off to a certain size, the angles must be chamfered while flattening. The dimensions are difficult to guarantee.
• (3) The focus of the production process of pipe plate forgings in the forging close to the process size, we should use the sample to compare in time to prevent the size exceeds the difference; forging process should be adjusted in accordance with the specific production conditions in time to adjust the process parameters and operating methods to ensure the finished size and internal quality of the forgings.

4. Production trial system

Combined with the above analysis and research, the new process was used for the production trial. Figure 3(a) is the schematic diagram of the two end angles after chamfering, and Figure 3(b) is the final forging finished products. Figure 3(b) is the final forging.

Figure.3 Tubesheet forgings (in kind)

During the trial production, we operated in strict accordance with the process parameters and controlled the anvil feeding and pressing volume reasonably, and completed the production of 4 pieces of half pipe plate, which all meet the delivery requirements after flaw inspection.

5. Conclusion

After analysis and production trial, the following conclusions can be obtained:

• (1) The new process of drawing square, flattening and chamfering at both ends is feasible for large-diameter tube sheets, which meets the customer’s demand for cost reduction.
• (2) Adopting the wide anvil and large press down method to forge the tube plate can effectively weld the internal defects, avoiding flake inclusions defects over the standard, and ensuring the internal quality of forgings.
• (3) Through the production of this tube plate, the innovative operation method provides technical support for the subsequent production of different types and specifications of forgings, and improves the overall manufacturing capability of Yaang.

Authors: Hu Zhenzhi, Song Xinshuang, Qin Hongfu, Zhang Ruihua, Zhao Lifeng

Source:  China Tube sheet Manufacturer: www.epowermetals.com

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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References:

• [1] Xu Shusen, Shi Yulin, Huang Guojun, et al. Research on forging process of large pipe plate [J]. Mining Machinery, 2002(4): 64-66.
• [2] Shi Yulin, Song Yubing, Xue Qiuyun. Process optimization of twice upsetting forged of large forgings[J]. Thermal Processing Technology, 2007(5): 51-53.
• [3] Gu Songxia. Optimization of forging process to improve the internal quality of 20MnMoNb pipe plate [J]. Large castings and forgings, 2005(1): 52-53.