Part 1: In-depth Analysis of Tube Sheet Connection Methods
Besides the basic classification, the applicability and technical points of each connection method are as follows:
Expansion Joint Principle: Utilizing mechanical expansion (rolling expansion) or hydraulic/liquid bag expansion, the heat exchange tube undergoes plastic deformation within the tube sheet borehole, tightly fitting the borehole wall. Residual stress is used to achieve sealing and resistance to pull-out.
Advantages: No thermal stress, no material fusion, relatively low requirements for tube sheet borehole machining, easy replacement of individual tubes during maintenance.
Disadvantages: Weak fatigue resistance; sealing performance is prone to degradation under high temperature, large temperature fluctuations, or severe vibration and corrosion conditions.
Applicable to: Commonly used in applications with low design requirements, mild operating conditions (e.g., low pressure, low temperature), or where welding heat effects must be avoided.
Welding Principle: Through a fusion welding process, the metal at the tube end and the bevel of the tube sheet borehole melts to form a continuous metallurgical bond.
Advantages: Highest connection strength, excellent sealing performance, able to withstand high pressure, high temperature, and severe temperature cycling.
Disadvantages: It generates welding thermal stress and deformation, requires high precision in tube sheet hole machining (bevel shape, cleanliness), carries the risk of welding defects (such as porosity, lack of fusion), and is difficult to repair after welding.
Applications: High pressure, high temperature, highly corrosive media, or applications requiring extremely high sealing performance.
Expansion welding principle: Expansion is performed first (applied expansion or strength expansion), then welding is performed. The sequence can be expansion before welding (expansion eliminates the gap between the tube and the hole wall, facilitating welding) or welding before expansion (welding ensures strength, expansion eliminates residual stress and enhances fatigue resistance).
Advantages: It combines the advantages of both—welding ensures strength and high-temperature sealing, expansion eliminates gaps, reduces stress corrosion and vibration fatigue, and significantly improves the lifespan of the joint under harsh operating conditions.
Applications: Modern high-standard heat exchangers, especially those used in environments with vibration, temperature fluctuations, and susceptibility to stress corrosion cracking (such as chloride ion environments).
Part Two: Detailed Explanation of KEPUNI Tube Sheet Welding Machine Core Technology and Applications
The KEPUNI system is an automated GTAW/TIG welding solution specifically designed for high-quality, high-efficiency tube sheet welding.
I. System Core Components and Functional Depth
High-Precision Welding Power Supply: Employs a digital inverter power supply with precise pulse control. Pulse welding effectively controls heat input, reducing welding deformation, and is particularly suitable for thin-walled tubes or heat-sensitive materials (such as titanium alloys and duplex stainless steel).
Intelligent Control System:
Parameter Storage and Recall: Hundreds of welding process parameter packages can be preset and stored for different materials (such as 304 stainless steel, 316L, carbon steel, and titanium) and different tube diameters/wall thicknesses.
Process Monitoring and Feedback: Real-time monitoring of arc voltage and current fluctuations, with integrated arc length adjustment to ensure stable welding processes.
Dedicated Welding Torch and Positioning Mechanism:
Welding Torch: Typically water-cooled, ensuring continuous welding over extended periods. The compact torch head design allows for deep penetration into densely packed tube sheet areas. An automatic centering device can be equipped to ensure the arc remains aligned with the joint center.
Positioning Device:A high-precision indexing plate or CNC rotary table ensures the welding torch rotates precisely and repeatedly around each tube. For deep-hole welding, an automatic Z-axis lifting system may be used.
Wire Feeding System:A precision servo wire feeding mechanism that synchronously controls the wire feeding speed and welding current, ensuring uniform molten metal filling and aesthetically pleasing weld formation.
II. Detailed Welding Process
Taking a typical tube-to-plate fillet weld as an example, the process typically includes:
Arrow Ignition and Preheating:High-frequency arc ignition at a set position preheats the weld initiation point.
Welding Stage: The welding torch rotates at a preset speed. The current, pulse parameters, and wire feeding speed automatically adjust according to the welding position (e.g., uphill, flat, downhill welding) to ensure uniform weld penetration and reinforcement height across all positions.
Cavity Filling and Arc Termination: At the end of welding, the current automatically decays to fill the crater and prevent crater cracking.
Hysteresis Protection:After welding, argon gas continues to protect the high-temperature weld to prevent oxidation.
III. Application Advantages and Value Demonstration
Superior Welding Quality:
Consistent Position: Automated welding overcomes the quality fluctuations caused by posture changes in manual welding.
High Metallurgical Quality: Sufficient argon protection results in clean welds and an extremely low defect rate.
Beautiful Weld Formation: Uniform and smooth welds reduce subsequent cleaning workload.
Extremely High Production Efficiency:
Continuous Operation: Compared to manual welding, there is no need for frequent electrode changes, slag cleaning, or breaks.
Quick Changeover: Switching between different pipe specifications can be done simply by changing the welding program, with short preparation time.
High Qualification Rate: Stable quality significantly reduces rework rates and shortens the overall manufacturing cycle.
Wide Material Adaptability: Stainless Steel Series: Austenitic, duplex/super duplex stainless steels, etc.
Special Alloys: Titanium and titanium alloys, nickel-based alloys (Hastelloy, Incol), zirconium, etc. These materials are extremely sensitive to welding heat input and protective atmosphere; automated welding is key to ensuring their weld quality.
Carbon Steel and Low Alloy Steel.
Meets high standards and specifications: Welding parameters are recorded and traceable throughout the entire process, fully meeting the requirements of ASME, PED, GB/T, and other domestic and international pressure vessel manufacturing standards for special equipment welding process qualification and control.
Summary: In modern high-end heat exchanger manufacturing, "expansion welding" has become the mainstream process. The welding process is rapidly transforming from manual operation relying on welder skills to automated and digital welding systems represented by KEPUNI. This is not only to improve production efficiency and reduce costs, but also to fundamentally ensure the safe, reliable, and long-life operation of equipment under increasingly stringent operating conditions and regulatory requirements, making it an inevitable choice for the transformation and upgrading of the manufacturing industry.