The Manufacturing and Assembly Process of Heat Exchangers

 
The manufacturing and assembly of heat exchangers involve precise technical requirements and complex processes at every step. From the fabrication of baffle plates to the assembly of tube bundles and the overall fitting, accuracy and attention to detail are essential throughout the entire process. As crucial equipment in industrial production, the performance of heat exchangers directly impacts the efficiency and safety of process operations, making each step critical.

Baffle Plate Fabrication

Baffle plates, located inside the heat exchanger, support and direct the fluid through parallel tube bundles. The fabrication process begins with cutting circular plates into shapes such as single-arc, double-arc, or ring shapes based on design specifications. A key focus during this process is ensuring consistent height for the tube holes, with strict requirements for hole concentricity. To achieve this, multiple baffle plates are often stacked and processed together to enable unified drilling and edge finishing.

During the baffle plate fabrication, spot welding is used to hold the plates in place on the same processing reference, ensuring uniformity. Once the tube holes are complete, the spot welds are removed, and further cutting and processing of the outer edges are performed. Additionally, to allow the heat exchange tubes to pass through the baffle plates smoothly, bolts and nuts are typically used for extra stabilization during outer surface cutting. Throughout this fabrication process, dimensions and positions are checked repeatedly to ensure high-precision machining and to avoid any deviations during subsequent assembly.

Tube Bundle Assembly

The assembly of the tube bundle is one of the core steps in the manufacturing of heat exchangers, with the accuracy of assembly directly affecting the overall performance of the unit. A tube bundle consists of components like tube sheets, baffle plates, spacer tubes, tie rods, and the heat exchanger tubes themselves. The assembly begins by securing the tube sheets, tie rods, and baffle plates to form a preliminary frame structure. Then, some heat exchange tubes are pre-installed, and once the overall structure is fixed, the remaining tubes are added one by one to ensure alignment with the holes in the baffle plates.

For small diameter fixed tube sheet heat exchangers (with baffle diameters not exceeding 1400mm), the tube bundle can be assembled outside the heat exchanger shell before being placed inside. However, for larger diameters (baffle diameters exceeding 1600mm), assembly must occur directly inside the shell. This increases the complexity of operations, especially when visibility is limited, making tube insertion more challenging and requiring more experience and skill.

U-Tube Bundle Assembly

The assembly of U-tube bundles requires even more precision and attention to detail. Since the U-shaped heat exchange tubes are arranged in layers, assembly starts from the innermost tube and progresses outward. The innermost tubes are secured first to ensure stability, and then layers are added outward until the desired tube bundle structure is formed. After all heat exchange tubes are installed, it is essential to add impact baffles, chutes, and necessary baffle components to ensure the overall stability and sealing of the bundle.

In the assembly of fixed tube sheet heat exchangers, one side’s tube sheet, baffle plates, tie rods, and heat exchange tubes are pre-assembled to create an initial bundle frame, which is then pushed into the heat exchanger shell. Finally, the tube sheet on the other side is installed to ensure a tight fit between the bundle and the shell, creating a complete heat exchanger unit.

Tube Sheet Welding

Welding the tube sheets is a crucial part of the assembly process. Due to limited cutting precision in the initial stages, a certain amount of machining allowance is typically left. During welding, it is essential to ensure that the protruding length of the heat exchange tubes is within the allowable range, and any excess must be cut to guarantee precise welding. The welding must strictly adhere to design standards, particularly to ensure the sealing between the tube sheets and the heat exchange tubes.

Assembly Considerations

Several important considerations must be strictly followed during the assembly of heat exchangers to ensure the final equipment performs effectively.

Perpendicularity of Heat Exchange Tubes to Tube Sheets: Ensure that the heat exchange tubes are vertical to the tube sheets to prevent damage during insertion or removal of the bundle.

Secure Tie Rod Fixation: Tie rods must be firmly secured during assembly, ensuring that nuts are tightened. This prevents movement of the tube sheet, which could damage the tube bundle during installation or removal.

Avoid Forceful Insertion During Tube Installation: External force should not be used to insert tubes. Avoid striking tube ends with metal objects to prevent deformation or stress, which could affect the performance of the heat exchanger.

Strict Control of Welding Areas: Apart from welding the tube sheets and heat exchange tubes, no other welding operations should occur to avoid damaging the device's structure.

Handling U-Tube Leaks: If leaks are found in U-tube heat exchange tubes, blocking measures may be taken, but the number of blocked tubes must not exceed 1% of the total bundle.

Overall Assembly of the Heat Exchanger

The assembly of the heat exchanger primarily involves the combination of the tube bundle, tube boxes, and the shell. For U-tube bundles, the tubes and tube sheets are pre-assembled and simply placed into the shell, with the tube boxes installed last. For fixed tube sheet heat exchangers, the assembly of tube boxes on both sides after inserting the tube bundle into the shell is particularly important, usually using bolt connections to ensure a tight fit. Care must be taken to align the tube ports with the design drawings to avoid assembly errors.

Heat Treatment and Non-Destructive Testing

Before the assembly is complete, critical components like the tube boxes and floating head end caps require heat treatment, especially the sealing surfaces of flanges and baffles. These areas undergo additional machining and heat treatment to ensure the accuracy of sealing and positioning after assembly. The precision finishing of the flange sealing surfaces is crucial as it directly impacts the overall sealing performance of the heat exchanger after assembly.

Once welding is complete, all welds must undergo non-destructive testing, typically using penetrant testing techniques to ensure there are no defects or cracks in the welded areas. Non-destructive testing is an essential step to ensure the long-term safe operation of the heat exchanger.

Pressure Testing

After assembly and inspection are complete, the heat exchanger must undergo pressure testing to verify its pressure-holding capacity. Since the tube side and shell side are two separate spaces, pressure testing must be conducted independently. Typically, the shell side is tested first, followed by the tube side. For specialized structures like floating head or reboiler heat exchangers, additional components may be needed to seal the testing space to ensure accurate results.

During the pressure testing process, strict control of the pressure differential between the shell side and tube side is necessary to avoid exceeding the design limits and risking equipment damage. After completing the pressure tests, all liquids inside the vessel must be thoroughly drained and dried to ensure no residual moisture remains.

Conclusion

The manufacturing and assembly of heat exchangers are highly precise processes that require close coordination at every stage. From baffle plate fabrication to tube bundle assembly and overall fitting to pressure testing, each step is vital. By strictly adhering to technical requirements and operational standards, we can ensure the efficient operation and long-term stability of heat exchangers, maintaining their critical role in industrial production.