The main manufacturing methods of spiral fin tubes are the above three. To facilitate analysis and comparison, spiral fin tubes are divided into welded fin tubes (high frequency welding, brazing) and integral spiral fin tubes for comparison.

Spiral finned tube welding rate

Welding rate is also called fusion rate

The welding rate is an assessment indicator of the width and total length of the fin weld. JB/T 6512-92 "Technical Conditions for Manufacturing High-Frequency Resistance Welded Spiral Fin Tubes for Boilers" stipulates that the weld fusion rate in the width direction of the steel strip shall not be less than 80%. Although the length direction is not mentioned, it can be understood that no less than 80% along the entire length of the fin is qualified.

The partial unfused length of the weld shall not be greater than the diameter of the pipe and shall not be greater than 50mm, and the number of unfused parts shall not exceed 2 per meter. Otherwise, repair welding shall be performed.

HG/T 3181-1989 "High Frequency Resistance Welded Spiral Fin Tube" stipulates that the sum of the actual weld lengths is not less than 90% of the total length of the fins, and the average width of the welds is not less than 80% of the fin width.

The welding rate of high-frequency resistance welded spiral fin tubes can actually reach 90%-95%. The welding rate of brazed spiral fin tubes is slightly higher than that of high-frequency welding, but the welding rates are not easy to check.

Integral spiral finned tube, as the name suggests, the fins are generated from the tube, there is no welding problem of the fins, and there is no need to check the welding rate.

Spiral finned tube weld tensile strength

JB/T 6512-92 stipulates that the tensile strength of the welded test piece shall not be less than 196MPa. HG/T 3181-92 does not provide for this.

For high-frequency resistance welded spiral finned tubes, the manufacturers weld tensile strength has reached over 200MPa, or even over 300MPa. The weld tensile strength of brazed spiral finned tubes can basically meet this requirement.

The fins of the integral spiral fin tube are extruded and rolled from the blank tube, so there is no problem with the tensile strength of the weld. The strength of the connection between the fin and the tube is equal to or even slightly higher than the tensile strength of the corresponding tube.

Post-weld heat treatment of spiral finned tubes

The heat-affected zone of the weld of high-frequency resistance welded spiral finned tubes is very small. Foreign standards stipulate that the heat-affected zone is <<0.8mm, and the measured heat-affected zone of some domestic manufacturers products is less than 0.5mm. Therefore, some standards do not provide for heat treatment after welding of high-frequency resistance welded spiral finned tubes. JB/T 6512-92 standard stipulates that finned tubes made of alloy steel should undergo stress-relieving heat treatment after welding.

The production process of integral spiral finned tubes is actually a process of extruding and rolling the original thick-walled billet tubes at high temperatures. After extrusion and rolling at high temperatures, there is no need for stress relief heat treatment at all.

Spiral fin tube heat transfer effect

The heat transfer effect of high-frequency resistance welding and brazing spiral fin tubes is at least 4 times higher than that of light tubes. The heat transfer effect of toothed fin tubes is better than that of complete fins. However, it should be noted that the welding rate of the weld between the fin and the tube is not 100%, and the standard stipulates that it is only over 80%. There is thermal resistance in the unfused part, which will affect the heat transfer effect.

The fins of the integral spiral fin tube are in 100% contact with the mother tube, plus the small R transition between the fin root and the mother tube when forming, not only increases the stiffness and pressure-bearing capacity of the fins, but also facilitates heat transfer. Its heat transfer effect is at least 5-6 times higher than that of light tubes, and is significantly better than the heat transfer effect of high-frequency resistance welding and brazing spiral fin tubes.

Spiral fin tube service life

The welding of high-frequency resistance welded spiral finned tubes is to apply pressure while melting at the contact point of the two metal surfaces. The welding rate is good. The corrosion resistance of the weld metal is more than doubled than that of brazing, which can greatly improve the fins. The service life of the tube. However, due to weak welding, long-term use can easily cause weld cracks, causing the fins to separate from the tube, thus affecting its heat transfer efficiency, and the fin tube has to be replaced.

Integral spiral finned tubes do not have fin welding problems, and there is no need to worry about fin corrosion, cracking, etc.