Application of all-position automatic tube sheet welding system in the manufacture of electric building condenser

Abstract : This paper introduces the application of full-position automatic tube sheet welding in its manufacture in combination with the manufacturing characteristics of the condenser in the electric construction industry.

Key words : electric construction; condenser; full position; tube sheet welding

introduction

In recent years, in order to meet the needs of the industry to rapidly develop electricity consumption, the construction of new power plants and power plant capacity expansion projects has been urgently pursued throughout the country, and the manufacture of large condensers is particularly important. The original condenser was manufactured using a copper tube expansion process. After long-term service, the equipment will cause leakage problems in the copper-green and copper pipe joints, which will seriously affect the heat exchange efficiency and service life, and the maintenance cost will be high in the later period. Therefore, at present, the condenser heat exchange tube is changed to Ti alloy in the coastal area to prevent Cl-corrosion, and the interior is changed to austenitic corrosion-resistant stainless steel, and the strength increase and sealing welding process is adopted to completely solve the leakage problem. The number of welded joints of the whole condenser tube plate is as high as 40,000 to 80,000, the workload is large, the manual operation is difficult, the construction period is tight, and the weld quality is high. Many factors determine the use of all-position automatic tube and plate welding equipment to weld the electric construction industry. The condenser is imperative. This paper focuses on the characteristics and application of full-position automatic tube sheet welding.

1. Condenser structure

The tube plate has a thickness of 30-50 mm, and the material is 304 stainless steel or a composite plate (the base layer is a 16 Mn coating of 5 mm Ti alloy). The heat exchange tube material and the tube sheet material are the same, and are 304 stainless steel or Ti alloy, and the specifications are generally Φ25×0.5 and Φ25×0.7. The connection method is strength increase and sealing welding. See the schematic diagram for the specific structure.
The nozzle extends 0-0.5mm, and the mouth of the nozzle rises about 30mm.

2. Features of all-position automatic tube sheet welding

The welding process of all-position tube sheet welding includes flat welding, up-slope welding, down-slope welding, and down-welding. The force of the molten pool varies.

1. The structure of the tube sheet

Gravity has different effects on the weld formation at each point: the flat welding position, gravity tends to cause the molten pool to flow into the nozzle; the position of the overhead welding, gravity easily makes the molten pool deviate from the weld, resulting in uneven weld formation.

In order to reduce the influence of the gravity factor on the molten pool, the all-position tube sheet welding is easy to use the pulse welding method, that is, the peak forms the molten pool, the base value maintains the arc not extinguished, and the molten pool is cooled. The weld is superimposed by very dense solder joints to form a weld that is well fused and has a uniform appearance.

3. Requirements for automation equipment for condenser tube sheet welding in the electric construction industry

According to the structure of the condenser, the self-fluxing and non-wire pulse TIG automatic welding process is adopted. The automatic welding equipment includes the welding power source and the gun head. The specific requirements are as follows:

3.1 Requirements for welding program-controlled power supply

1) The power supply should have advanced air supply, delayed air supply, high frequency arcing, pulse current regulation, automatic rotation, counting, current attenuation and other functions.

2) Power programmable memory, user-friendly programming interface, easy to operate, easy to use.

3) The power supply should have a high-performance Multi-cpu system with fast response, high control accuracy, stable performance and good weld reproducibility.

3.2 Requirements for tube sheet welding gun head:

1) There should be a reliable positioning device and quick positioning.

2) There should be a reliable gas protection device.

3) Compact structure and high precision.

4) The welding torch should have external circulating water cooling to meet long-term work requirements.

5) Light weight and reduce labor intensity.

4 Condenser assembly, cleaning and on-site construction requirements

4.1 Assembly requirements

1) The length of the tube plate extension pipe should be strictly controlled 0-0.5mm

2) After one end is raised, the other end uses a tube end face machine to remove excess nozzles.

3) The riser should be uniform and avoid the situation that the stick is not up.

4.2 Cleaning requirements:

1) Strictly clean the pipe hole and the nozzle within 25mm of oil and moisture before wearing the pipe

2) After the pipe is finished, it should be cleaned with organic solvent to ensure that the welding area is free of oil, so as to avoid the occurrence of air holes during welding.

4.3 On-site construction requirements:

1) A tarpaulin should be built at the site to prevent the tube sheet from absorbing moisture.

2) When constructing at one end, the other end of the nozzle is preferably sealed to prevent arcing from affecting the arc.

5. Welding process and efficiency

Take the nozzle of welding Φ25 as an example. The time for welding one nozzle is 30-50s, and the number of welded nozzles for 8 hours is 500-800.

6. Welding results

The condenser of the electric construction industry adopts the full-position automatic tube and plate welding equipment through the on-site construction welding as shown in Fig. 3. The welding effect is shown in Fig. 4.

6.1 The weld bead is beautifully formed and the weld is silver-white;

6.2 High welding quality and good reproducibility of welding;

6.3 PT coloring inspection without pores, cracks;

6.4 Passed the on-site hydraulic test;

6.5 High welding efficiency.

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