Manufacturing technology of 30° pipe bend for hydrogenation reactor

Introduces the hydrogenation reactor 30 ° bend under the material, curved type, processing, wall surfacing, and other technology and production process.

A hydrogenation reactor is a refinery hydrogenation device in the key equipment; its equipment in high temperature, high pressure, hydrogen and hydrogen sulfide, and even more sulfuric acid corrosion of harsh environments; the design of the equipment uses hydrogen-resistant steel and must be in contact with the media in the inner wall of the welded stainless steel material, to meet the requirements of the equipment used. Hydrogenation reactor equipment generally consists of a cylinder, upper and lower head, take over the flange and upper and lower import and export elbow and other components, including upper and lower import and export elbow special, so how to realize the hydrogenation reactor upper and lower import and export elbow stainless steel surfacing of the inner wall is a key link in the manufacture of equipment. At present, due to the capacity of the equipment, the size of the pipe, and the structure of the reasons, usually the manufacturing of the pipe is usually used in segmented welding, and then the use of electrode arc welding for welding into the process method. This article focuses on the 30 ° bend of the manufacturing process, such as: casting expansion, forging process, material, curved type, processing, welding, etc.

1. Manufacturing process of 30 ° bend

The manufacturing process is: feeding expansion → steelmaking → forging → rough machining → testing → finishing → splitting → heating → curved → tempering heat treatment → performance → processing bevel → surfacing.

2. Manufacturing engineering of 30 ° bend

2.1 Feeding Expansion

General hydrogenation reactor top and bottom bends of different sizes, so separate feeding production, but three 30 ° bends when feeding the joint forging feeding, curved before splitting, so to determine the feeding size of the bends need to be unfolded, and discharged, the specific expansion and discharged as follows.
The total length of feeding = 2 x L + l + 180mm (processing) + 40mm (cut amount) + 200mm (performance review material)
Where:

L = π (R + D/2 + δ)/6
L = π (R – D/2)/6

In the formula:

• R is the radius of curvature of the bend.
• D is the inner diameter of the bend; δ is the wall thickness of the bend.

Figure.1 Bending pipe discharging diagram
The bending pipe discharge is shown in Figure 1.

2.2 Forging

According to the feeding size and product technical conditions for forging, and then rough machining according to the drawing requirements, after passing the test, according to the product drawings and technical conditions for finishing and testing, after passing the transfer to the next sequence.

2.3 Materialization

Because of the bending material, when three bends were forged into a straight pipe, it curved before the requirements of the drawings for the number of materials and material. Before the material numbering according to the drawing dimensions of the production of special samples for the number, the end of the bend to leave 30mm processing, leaving 20mm cut. Undercutting using the flame gas cutting method; gas cutting cuts are flat, less than 10mm wide.

2.4 Curving

The press does the curving; the process is hot, and the specific curving steps and precautions are as follows.
(1) Selection of tire. Bend pipe curvature is best to use a special tire curvature, but to reduce manufacturing costs and shorten the production cycle; you need to borrow the existing tire; tire selection principles are as follows:

• 1) The inner diameter of the tire than the outer diameter of the pipe bend 0.8% – 1%;
• 2) The angle of the tire must be greater than or equal to the angle of the pipe bend;
• 3) The bending radius and the current product bending radius cannot be too big a difference, generally ≤ ± 100mm. The tire’s status to borrow can not meet the requirements of the bend curve before the curve must be transformed according to process requirements.

Figure.2 Internal support

Figure.3 Support assembly form
(2) Assembly of internal support. To better ensure the quality and size of the curved pipe shape, curved pipe before the need for special support to fix the size of the pipe bends, support forms, such as Figure 2, and assembly forms, such as Figure 3.
(3) Workpiece heating. Bend before the curved type of heating in the furnace, heating temperature to meet the requirements of the curved type (950-1050 ℃), heating three bends, and double-checking the material simultaneously. Selecting a heating furnace as close to the press as possible ensures the curve works smoothly.
(4) Curve. Curved pipe bending press to complete. Curved process considerations are as follows.

• 1) Tire installation of the upper and lower tire center must be in a plane.
• 2) The workpiece on the tire must be symmetrical to ensure a curved angle.
• 3) Bend pipe curvature using a special sample plate for delivery inspection.
• 4) Curved as much as possible during the preparatory work to ensure the curved process is smooth and successful. To avoid the second heating calibration, the curved pipe curved termination temperature should be > 750 ℃.
• 5) Curved with an asbestos cloth cover after slow cooling.

(5) Cleanup and delivery inspection. Curved gas cutting after the removal of the inner support of the bend, using a low-stress punch in the bend surface printing furnace (card) number, the number of stamps, and check the geometry of the bend and oval degrees of the map, qualified to turn the next sequence.
(6) Tempering. Bend curve type qualified according to a special process for tempering, tempering performance test material, and bends in the same furnace.
(7) Testing, sandblasting. Bend after the performance of qualified tempering, with a baking gun to remove the inner and outer surface of the bent oxide skin, and grinding wheel grinding inside and outside the surface of the magnetic particle test, ultrasonic testing. Inner and outer surface sandblasting to remove rust.

2.5 Processing bevel

Bend ring beveling using boring machine processing, processing must ensure that the angle of the bend and weld bevel, after processing the surface of the weld bevel to do 100% magnetic particle testing, after the overall quality of the pipe bending cross-checking, after passing to the next sequence.

2.6 Wall Surfacing

30 ° bend wall surfacing process according to the bend diameter, weight, and radius of curvature, commonly used surfacing methods are the SMAW method of surfacing, TIG method of surfacing, and FCAW method of surfacing. If the inner diameter of the bend is less than Ø160mm, the SMAW method of surfacing; if the outer diameter of the bend is less than Ø550mm or the weight is less than 500kg, the TIG method of surfacing, the rest of the bend FCAW method of surfacing.

2.6.1 Bend SMAW method of surfacing

SMAW method of surfacing is the most basic surfacing method; due to low surfacing efficiency, the surfacing layer surface is not flat enough, labor intensity, so generally seldom used, only bends with an inner diameter of less than 60mm cannot be realized automatically surfacing method of surfacing SMAW method of surfacing. SMAW method of surfacing using a short-arc operation straight into the welding, surfacing welding specifications, preheating temperature, Interlayer temperature, and other requirements are detailed in Table 1. General bends are 3 layers of surfacing, 1 layer of transition layer + two layers of the surface layer to meet the requirements of the drawings.

2.6.2 Bend TIG method of overlay welding

TIG surfacing method is one of the most commonly used surfacing methods, with good quality, high efficiency, low labor intensity, and other advantages of surfacing. The following 2.25Cr-1Mo steel 30 ° bend wall surfacing TP309L + TP347 double layer surfacing is an example of 30 ° bend surfacing main steps and considerations.
(1) Confirm that the workpiece is on the order of qualification, check the size, clean up the surface to be surfacing, and enter the surfacing parameters.
(2) Bend pipe surfacing machine clamped firmly, 4 claws uniform force, the surfacing process cannot be loose, and to find the right, scratch surfacing start line.
(3) The use of liquefied petroleum gas flame preheating workpiece, preheating temperature ≥ 120 ℃, surfacing process workpiece temperature shall not be lower than the preheating temperature.
(4) Bend using fully automatic TIG equipment for TP309L surfacing, welding specifications Ø 1.2mm stainless steel solid wire, surfacing process specifications, preheating temperature, interlayer temperature requirements in Table 2. surfacing layer from the end face distance as far as possible, in line with the requirements of the drawings, to facilitate the bending of the group welding weld seam after the back of the surfacing of stainless steel.

Table.1 SAMW surfacing process specifications

Weld overlay	Specifications/mm	Electrode	Current A	Voltage V	Speed mm/min	Preheat Temperature/°C	Interlayer temperature/° C
Transition layer	Φ5	DC/RP	180-240	24-28	150-280	≥120	≤ 250
Surface	Φ5	DC/RP	180-240	24-28	150-280	–	≤ 100

Table.2 Automatic TIG surfacing process parameters

Weld overlay	Specifications/mm	Electrode	Current A	Voltage V	Speed mm/min	Swing mm	Preheat Temperature/°C	Interlayer temperature/° C
Transition layer	Φ1.2	DC/RP	220-240	15-20	180-230	7 (average)	≥120	≤ 250
Surface	Φ1.2	DC/RP	220-240	15-20	180-230	7 (average)	–	≤ 100

(5) TP309L surfacing layer appearance check.

(6) Surfacing layer cooling to room temperature after the surface of the surfacing layer using a non-ferrous ion grinding wheel for grinding and cleaning to meet the penetration testing requirements.
(7) Surface cladding layer for 100% penetration testing, testing standards by the relevant technical conditions.
(8) Bend welding machine clamped firmly, 4 claws uniform force, the surfacing process can not be loosened, and find the right, row surfacing start line clamping, cleaning up the residue after penetration testing.
(9) Bend using fully automatic TIG equipment for TP347 surfacing, welding specifications Ø 1.2mm stainless steel solid wire, surfacing process specifications, interlayer temperature requirements see Table 2. surfacing layer according to the drawing requirements, if the total thickness of product surfacing layer requirements 6.5mm, TP347 surfacing layer; if the total thickness of the product surfacing layer requirements 7.5mm, TP347 surfacing needs 2 layers. If the total thickness of the product cladding layer is 7.5mm, then TP347 needs to be clad with 2 layers. Surfacing layer from the end face distance as far as possible equal, in line with the drawing requirements, to facilitate the bending of the weld after welding the back of the weld seam surfacing stainless steel.
(10) According to the requirements of the technical conditions of the product TP347 surfacing layer sampling, sampling at the grinding test, sampling at the filler weld, etc., after the completion of the work of the surfacing layer surface as a whole grinding and cleaning to meet the requirements of penetration testing.
(11) According to the requirements of the technical conditions of the weld surface, use a ferrite measuring instrument to measure the ferrite content of the TP347 stainless steel cladding layer.
(12) Surfacing layer surface to do 100% penetration testing, 100% magnetic particle testing, and testing standards by the requirements of the relevant technical conditions.
(13) Bend pipe cladding layer quality as a whole for inspection.

2.6.3 Bend FCAW method of overlay welding

Another commonly used surfacing method is FCAW surfacing, a general bend outside diameter greater than Ø550mm or weight greater than 500kg of the bend are used FCAW method of surfacing. In order to better ensure the quality of the surfacing layer and reduce labor intensity, the use of a vertical turntable and special cross-slide frame to achieve the ultimate semi-automatic FCAW surfacing, thus obtaining better results and make up for the limitations of the fully automatic TIG equipment capacity. The FCAW surfacing sequence is the same as TIG surfacing.

2.7 Welding

After the 30°pipe bend passes the inspection, it is welded with the corresponding flange and pipe in a reasonable process sequence. Usually, it adopts the TIG + SMAW weld method to meet the manufacturing needs of the hydrogenation reactor.

3. Conclusion

• (1) 30 ° bend manufacturing technology has matured, and the quality of each link is very stable, fully able to meet the needs of various specifications of hydrogenation reactor manufacturing.
• (2) There are three kinds of surfacing methods for 30° bends, among which the fully automated TIG surfacing method is widely used in production due to its very good quality of the surfacing layer, high productivity, low labor intensity, etc. Only when the equipment capacity and the size of the bends do not allow TIG surfacing to be realized the other two surfacing methods are chosen.

Author: Bao Guoping