Study on flanging process of large diameter tee

This paper mainly expounds the new technology of tee flanging forming, and analyzes a large diameter equal tee D735×735×735 (SA-335P91).

The results show that the flanging forming method of tee can improve the forming quality of tee branch and reduce the manufacturing cost of tee. The flanging forming process can be widely used in the manufacture of large tee in boilers and oil and gas pipelines.

Tee is one of the structures that must be used in boilers and oil and gas pipelines, and it is an important pressure connecting part between header and pipeline. At present, the tee pressing method of most companies is the tee pressing technology imported from CE company of the United States, which is mainly used for the pressing and forming of thick wall tee. Large diameter seamless thick wall pipe (the diameter of seamless blank pipe is about 1.6 times of the finished product) or steel plate (in order to reduce the cost, the steel plate is pressed into cylinder several times and welded into blank pipe) are used as blank, The forming of an equal diameter tee needs about 12 passes of extrusion forming (6 passes) and shaping (6 passes) with multiple sets of dies in the press. If it is a different diameter tee, it needs to be selected according to the reduction amount for several times of pressing and necking (one reduction amount is 2 “), and the maximum size of the tee that can be pressed is D610. This forming method is still used for medium and thin wall tees, so the production cost and material cost are high.

The main shortcomings of the tee formed by multiple pressing are as follows:

  • (1) The straight length of the branch pipe of the tee is not enough;
  • (2) The pipe part of the tee branch pipe is irregular spherical, and the curved surface accounts for 2/3 of the whole length of the formed branch pipe.

The inclined surface of the tee’s branch pipe needs to be smoothed by surfacing welding (see picture 1 for details).

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Fig.1 the end of tee branch pipe is irregular and needs to be welded smoothly

Flanging process of tee

At present, the main problem of extruded tee is that the effective length of tee branch is not enough, and the end of extruded tee branch is irregular spherical. How to take effective measures to turn part of the curved surface into a straight branch is the key to the research of tee manufacturing technology.
According to the existing equipment situation of Dongfang Boiler and the research and analysis of the manufacturing methods of tee at home and abroad, a new manufacturing method of tee is proposed: the new tee is formed by pre forming + drawing flanging + shaping instead of the original extrusion forming. The process can reduce the diameter of the blank steel pipe, reduce the number of tee pressing forming, and effectively ensure the forming quality of tee branch pipe, avoid the surfacing process.

Steps of tee process

The main steps of tee process are as follows:

  • (1) The steel pipe blank with larger specification is selected and preformed;
  • (2) Drawing flanging forming, flanging out branch pipe;
  • (3) Extrusion shaping, meet the size requirements of tee. See Figure 2.

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Fig.2 process diagram of tee

Technical characteristics of tee forming

The flanging forming method is only suitable for medium and thin wall, but it is not feasible to make straight hole flanging in the pipe blank to make large diameter equal tee. Because of large deformation, the height of branch pipe formed by tee cannot be guaranteed. The hole is large and the height of flanging branch pipe is not enough; If the hole is small, the deformation of the branch pipe is too large, and the die is wrapped until the tensile deformation reaches cracking. Pre forming, that is, a certain amount of bulge is needed at the forming part of the branch pipe (as shown in Figure 3), the hole is opened in the bulge, and the flanging mode is turned into a vertical straight edge under the action of the die, so as to meet the product quality requirements. The key of this technology lies in the following aspects:

  • (1) Making the whole forming process;
  • (2) Calculate the pre deformation (branch bulge);
  • (3) Determine the appropriate form of opening;
  • (4) The pipe blank is selected;
  • (5) Die structure design;
  • (6) Make sure there is enough plastic.

Different from steel plate flanging forming, flanging process is complicated. In hot state, flanging die must be transferred from blank main pipe to pull rod and fixed to complete flanging process.

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Fig.3 tee bulge forming diagram

Formulation of process plan

Reasonable distribution of the amount of pressure drum and flanging to ensure the length of the branch and thinning. The flanging process is arranged in the whole forming process, which is based on the amount of pre forming and the form of opening. The preforming mode is pressing mode, and the pressing die is used for multiple forming. It should also be considered that the flanging is easy to operate, the mandrel should enter from the main pipe, and the clearance between the mandrel and the inner diameter of the main pipe is reasonable; It is too small and difficult to operate in hot state; Too large, increase the process, directly affect the production efficiency and economy. When flanging, the diameter of the main pipe is larger than that of the branch pipe, so it needs to be shaped or formed + shaped after flanging.

Mold design of tee

The die structure is determined by the pressing process. On the premise of ensuring product quality, reduce mold manufacturing cost as much as possible. In the die design, the first thing to consider is the possibility of forming, mainly to determine the amount of pressure drum and flanging, which is the key of tee manufacturing process. Secondly, the die structure should be universal and easy to operate. Mold design: in order to reduce the cost of mold manufacturing and easy operation, pre forming needs one forming.

The pull rod device and flanging die are the key to successful implementation. The structure meets the requirements of convenient operation, reducing flanging force and ensuring forming quality.

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Fig.4 Schematic diagram of tee flanging die

Calculation of flanging force F:

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When the maximum flanging force is less than 85% of the pull force under the pull rod device, flanging may be formed at one time; Otherwise, the flanging times need to be increased (see Figure 4 for details).

Process validation

The choice of tee

During verification, we selected a specification with greater manufacturing difficulty and higher material grade for trial production, and the specification is dw735 × seven hundred and thirty-five × 735, SA-335P91(See Figure 5).

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Fig.5 tee of test piece

Manufacturing process of tee

The pipe blank is preformed to 32″ for opening. Considering the water pressure allowance and groove processing of about 50 mm at the end, the distance from the end of the branch pipe to the center line of the straight pipe is 550 + 50 = 600 mm, so the shortest effective height of the branch pipe must be 600-406 = 197 mm. In the process of pipe blank pressing, the diameter of pipe blank decreases, the thickness of pipe blank increases and the length of pipe blank increases.

First, the new tee bulge is formed by extrusion, then the hole is opened, and then the flanging tee branch pipe is drawn on the hydraulic press, and finally the shaping process is carried out((see Figure 6)

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Fig.6 process flow chart of tee of test piece
In the manufacturing process, because the pipe blank is large and thin, and the temperature drops rapidly, the high temperature tensile strength of P91 increases sharply. In fact, the flanging force at 700 ℃ ~ 750 ℃ is more than twice that at 900 ℃, which has exceeded the equipment capacity. In fact, it can not be flanged at one time, but needs to be flanged twice (as shown in Fig.7 and Fig.8).

Verification of tee test data

After the forming of the tee, the main parameters of the tee were measured, including the wall thickness of the tee branch, the diameter data of the tee and the length data of the tee branch. See tables 1, 2 and 3 for details.

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Fig.7 Schematic diagram of opening on drum of tee branch pipe

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Figure 8 the real object of tee

Table.1 wall thickness data of tee branch pipe mm

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Table.2 tee diameter data mm

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Table.3 length data of tee branch pipe

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The test data show that:
In this experiment, after drawing and extrusion, the height of branch pipe h is:

The effective net height of branch pipe H = 580-30 = 550 mm;

The following conclusions can be drawn from the measured data and dimensions:

  • (1) The trial tee meets the requirements of branch pipe length.
  • (2) The trial tee meets the requirement of minimum wall thickness of 35mm.
  • (3) Through the wall thickness measurement, meet the requirements of the standard δ B = 35 mm.
  • (4) The shape and other dimensions meet the requirements of the standard.
  • (5) The forming of tee branch pipe is good, and no surfacing is needed.

Conclusion

The branch pipe of tee manufactured by flanging forming process has high forming quality, high efficiency and less molds, which can save a lot of manufacturing cost. It is suitable for the manufacture of large diameter and high pressure resistant tee, and can be widely used in boiler and petrochemical industry. The process is mature and reliable, and has wide application prospect.
Authors: Wang Dongping, LU Hong, Zhang Jun

Source: Network Arrangement – China Large Diameter Tee Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

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