tubeTube-to-tube-sheet welds are an essential step in the manufacturing process for heat exchangers, steam turbines, condensers, air coolers, and boilers. In this process, metal tubes are mounted on tube sheets and welded using gas- TIG ing (GTAW) to ensure optimal performance and durability.
benefits orbital welding , whether automated or manual
Automated "tube" to tube sheet welding has replaced manual welding to improve the productivity and reproducibility of " tube" tube sheet joints and to shorten the production times of industrially manufactured tube heat exchangers. TIG-orbital welding achieves a significant increase in productivity, as the mechanized or automated welding processes are highly repeatable and minimize welding defects and repair work. This welding technology ensures consistently high quality, as every successful welding sequence can be repeated flawlessly an infinite number of times. In addition, trained specialists are able to operate orbital welding machines effectively after receiving appropriate instruction. This reduces dependence on hard-to-find and expensive manual welders and lowers labor costs.
Optimum equipment for automated tube tube-to-tubesheet welding
The equipment used for automated tube tube sheet welding should be strictly adapted to the application and the desired degree of automation:
Three axes (gas, electricity, rotation): A welding power source (IM-2020-MC-P) and an tube-to-tube-head welding head (T-250 or T-230-MC) perform the welding without filler wire.
Four axes (gas, power, rotation, wire): A welding power source (IM-2020-MC-P) and an tube-to-tube-head welding head (T-250 or T-230-MC) perform the welding using filler wire. Two passes are typically welded in two steps.
Five axes (gas, power, rotation, wire, motor control): The power source IM-2020-MC-P for controlling five axes and a " T-230-MC" welding head with motor
The right planning and preparation for high-quality tube tube-to-tubesheet welds
Successful orbital " TIG" welding requires careful planning and preparation:
fixing: The tubes must be precisely centered and secured in the hole in the tube end plate so that the gap between tube and the hole is completely closed. The Technodata TES-97 securing tool is ideal for this purpose.
No stapling: Stapling the tubes should be avoided in order to prevent additional heat input, excess material at the stapling points and non-centric positioning of the tubes .
No expanding: The tubes must not be rolled in before welding to allow degassing during the welding process.
Cleanliness: A clean contact zone between tube and the tube sheet is crucial to avoid the formation of pores.
Seamless tubes: Seamless tubes or tubes with a flattened weld seam should be used.
Chamfer: Joints should be provided with J-preparations to ensure reliable melting of the tube edge base.
Different pipe positions and what to look out for
Flush tubes
Depending on the application, the welding of flush tubes can be carried out with or without filler wire. Without filler wire, a seam preparation without bevel is used.
Typical applications include welded joints in thermal power plant condensers, often with titanium tubes and titanium-coated tube sheets.
Welding equipment with four or five controlled axes ensures precise welding work. A motor control system and an additional protective gas chamber are optional, but necessary for materials such as titanium or zirconium.
The torch angle should be 0° or 15° depending on the requirements. The V-seam can be avoided by suitable processing of the tube sheet, and J-seam preparations are preferable.
Protruding tubes
Protruding tubes are always welded with filler wire. The torch angle and the pipe protrusions must be carefully adjusted. Standard angles are 15° or 30°.
A torch angle of 15° is suitable for thin-walled tubes (1.6 mm to 2.11 mm) to prevent the inside from melting.
A torch angle of 30° is suitable for thick-walled tubes from 2.5 mm if the distance to the surrounding tubes is sufficient.
The pipe overhang should be at least 5 mm to prevent the tube ends from melting.
Reset tubes
Welding equipment with four or five controlled axes is required. The Motor Control function of the T-230-MC is particularly recommended for recessed tubes .
V-seam preparation of the tube sheet is possible. Depending on the pipe dimensions, one or more welding layers are required.
Typical application: Welding behind the tube sheet of a double-walled collector for air cooling or liquid condensation.
Internal tube welding behind the tube sheet (inbore welding)
This method is used to prevent crevice corrosion between the tubes and the tube sheet.
Requires precise workpiece preparation and perfect control of the welding process.
Inert gas covering of the seam root is required, except for standard seam preparation without a weld joint.
Root protection can be achieved by flooding the container or by local gas protection.
Internal pipe welding is possible with filler wire for pipe diameters larger than 35 mm.
The horizontal welding position is advantageous for thick-walled tubes (3 mm to 3.6 mm).
The distance between the front edge of the tube sheet and the welding joint must be maintained precisely, as the welding process cannot be observed directly.
Welding equipment with three or four controlled axes is required; five axes are required for standard seam preparation without a weld joint. A special Inbore welding head must be available.
Conclusion
Careful planning and preparation are crucial for successful and high-quality tube tube-to-tubesheet welds. By adhering to these detailed requirements, mechanical stresses can be minimized and the specific requirements of each application can be met. The choice of the right equipment and the precise execution of the welding process guarantee durable and reliable connections.
The Right Welding Technique for Your Application
Whether pipe welding heads for standard applications or special torches for hard-to-reach geometries: We’ll work with you to determine which solution is right for your heat exchanger. All systems are also available for rent.