Technical Design Guide: Essential Requirements for Automatic U-Tube Orbital Welding
U-tube orbital welding: select the clamp from the joint drawing
The FYID-Feiyide FXT-U system pairs an FXT20 Pro power source with one selected U12, U16, U21 or U25 enclosed welding clamp. It is intended for socket or butt welding between a straight tube and a U-bend in heat exchangers, refrigeration equipment and surface air coolers. The current configuration guide covers thin-wall carbon steel and stainless steel tubes. Do not select a clamp from tube OD alone: the end-plate layout, weld height, U-bend straight section, insertion and free space around the weld all matter.
Current clamp selection table
| Requirement | U12 | U16 | U21 | U25 |
|---|---|---|---|---|
| Tube outside diameter | 12.7 mm | 12.7–16 mm | 16–21 mm | 20–25 mm |
| Weld position above end plate | ≥28 mm | ≥36 mm | ≥36 mm | ≥38 mm |
| U-bend straight-section length | ≥36 mm | ≥44 mm | ≥44 mm | ≥48 mm |
| Total straight section after insertion | ≥68 mm | ≥80 mm | ≥80 mm | ≥86 mm |
| Insertion depth | 5–8 mm | 5–8 mm | 5–8 mm | 5–8 mm |
| Required clearance radius around weld tube center | 24.5 mm | 32 mm | 36 mm | 40 mm |
| Clamp weight, excluding cable | Approx. 4 kg | Approx. 4 kg | Approx. 4 kg | Approx. 4 kg |
The clearance values are obstacle-free radii measured from the center of the tube being welded; they are not minimum tube center-to-center spacing values. The socket-joint limit is a combined wall thickness of no more than 1.6 mm for the two tubes. For a butt joint, the tube wall limit is 1.6 mm. Tube preparation, fit-up and internal argon purging must follow the qualified procedure. Special crossed-tube or manifold layouts require technical review and may not be weldable with a standard clamp.
Power source, shielding and records
The FXT20 Pro uses single-phase 220 V ±10%, 50/60 Hz input and provides 5–200 A DC output. It combines PLC control, a 10-inch touchscreen, interval/zone parameter control, 200 stored program sets and a built-in circulating-water system for the welding clamp. The power source weighs 20 kg and the standard clamp cable is 6 m. Argon is required for welding shielding; the tube interior must be purged with argon for socket welding and for easily oxidized materials needing back-side protection. The guide specifies one-key parameter printing, not USB export of weld datasets.
What to send for an access check
Provide the tube and end-plate drawings, tube OD and material, both wall thicknesses, end-plate hole center distance and pattern, straight-tube projection, U-bend straight-section length, insertion depth, joint type and intended weld-before-expand sequence. FYID-Feiyide can then check the selected clamp against the actual geometry and discuss qualification and quotation. For the current system configuration, see the FXT-U U-bend welding product page.
Selection questions
Is there one minimum center-to-center tube spacing for all FXT-U clamps?
No. The configuration guide specifies obstacle-free radii measured from the center of the weld tube: 24.5 mm for U12, 32 mm for U16, 36 mm for U21 and 40 mm for U25. It does not give one universal minimum tube center spacing. Send the end-plate layout for review.
Is U20 a current FXT-U clamp?
No. The current configuration lists U12, U16, U21 and U25. The U21 clamp covers 16–21 mm tube OD.
What internal argon flow rate should be set for U-tube welding?
The guide requires argon shielding and tube-interior purging, but does not give one flow rate for every tube size and joint. Confirm gas flow and pre-purge settings in the qualified welding procedure.
Can the assembly be welded before tube expansion?
Yes. The configuration guide specifies welding first and expanding afterwards. Confirm the joint, fit-up and inspection procedure for the actual tube bundle.
Does the FXT20 Pro export per-joint weld datasets over USB?
The U configuration guide specifies one-key parameter printing. Do not assume USB weld-data export or automatic PQR generation; confirm the documentation needed for the project separately.