Monolithic finned tube

Integral spiral finned steel tubes are manufactured using hot-rolled finning machines to press and roll No. 20 steel tubes conforming to the GB/T3087-2008 standard "Seamless Steel Tubes for Low and Medium Pressure Boilers" or 20G steel tubes conforming to the GB/T5310-2017 standard "Seamless Steel Tubes for High-Pressure Boilers" as the base tubes, forming spiral finned heat exchange tubes with an integrated structure of fins and base tubes.   

Integral spiral finned tubes are primarily used as next-generation heat exchange components for medium and high-pressure boiler economizers and air preheaters, offering advantages such as "high efficiency, energy savings, economy, resistance to ash accumulation, wear resistance, long service life, and strong environmental adaptability." Compared to conventional bare tubes or high-frequency welded spiral finned tubes, the integral spiral finned tubes produced by our company possess the following technical advantages: 1. No welding required, longer service life. Integral spiral finned tubes eliminate the need for welding, completely removing the contact thermal resistance between the fins and the base tube and the issue of fin loosening. They exhibit high efficiency, stability, and reliability in heat transfer performance, with a longer service life, making them particularly suitable for harsh environments, such as economizers in circulating fluidized bed boilers with high flue gas velocity and hard particles. The weld adhesion rate of welded finned tubes is difficult to achieve 100% and is challenging to inspect. Welding creates contact thermal resistance and requires post-weld thermal stress treatment. Long-term use can easily lead to weld cracking, causing the fins to detach from the tube, resulting in greater contact thermal resistance and reduced heat transfer efficiency, necessitating the replacement of the finned tubes.

If a crack gap is 0.1 mm, and the thermal conductivity of air is 0.021 kcal/m²·h·°C, the thermal resistance reaches 0.0045 m²·h·°C/kcal, equivalent to the thermal resistance of a 180 mm thick steel plate. Integral finned tubes do not suffer from the aforementioned issues associated with welded fins. Their service life is equivalent to that of the base tube material, which is 3-4 times longer than that of high-frequency welded or brazed spiral finned tubes. Higher heat transfer efficiency. Taking economizers as an example, the overall heat transfer coefficient on the flue gas side outside the tube is generally no more than 100 kcal/m²·h·°C, while the heat transfer coefficient of water inside the tube is as high as 5000~10000 kcal/m²·h·°C. Therefore, the flue gas side heat transfer plays a dominant role in the process. According to the flue gas side heat transfer formula Q=kF?t, increasing the heat transfer area enhances heat transfer. The single-tube heat transfer test report from the State Key Laboratory of Multiphase Flow in Power Engineering at Xi'an Jiaotong University indicates that the heat transfer coefficient of integral spiral finned tubes is 6~7 times that of bare tubes. The thermal performance test report for finned tube bundles also points out that the Nusselt number Nu of integral spiral finned tube bundles is about 4 times that of bare tubes, with a significantly higher heat transfer coefficient, indicating markedly enhanced heat transfer performance. In contrast, relevant research literature on welded spiral finned tubes indicates that their heat transfer coefficient generally does not exceed that of bare tubes by such a margin, and the Nusselt number Nu of their tube bundles is about 4 times that of bare tubes. Additionally, integral finned tubes do not have the inherent contact thermal resistance and weld adhesion rate issues of welded types; the fin roots feature a small R smooth transition; and the longitudinal section of the fins has a trapezoidal structure. These characteristics make the heat transfer effect of integral finned tubes significantly superior to that of high-frequency resistance welded and brazed spiral finned tubes. Less prone to ash accumulation, slagging, and clogging. Removing ash, slag, and fouling from heat transfer surfaces is an important maintenance task for heat exchange equipment such as economizers.

Since the thermal conductivity of the ash and slag layer on the flue gas side of the economizer is very low, even a thin fouling layer can create significant thermal resistance. Each millimeter of ash and slag layer is equivalent to a 400 mm thick steel wall. The presence of fouling thermal resistance not only reduces heat transfer but also causes a significant rise in tube wall temperature, which can easily lead to tube wall overheating and burnout, potentially causing accidents. The integral finned tubes have a small R smooth transition between the fin roots and the base tube, with a smooth surface, eliminating the issues of ash accumulation, slagging, and clogging that occur in welded finned tubes due to folded and uneven fin roots. Even if a small amount of ash accumulates, it is easily blown off, ensuring effective heat transfer and improving operational economy. Greater tensile strength, pressure resistance, and wear resistance. Integral finned tubes are formed by extruding and rolling thick-walled tubes, essentially subjecting the tubes to an additional high-temperature rolling process.

Safety performance evaluation reports from the China Special Equipment Inspection and Research Center and comprehensive technical inspection reports from the National Steel Product Quality Inspection Center indicate: The longitudinal tensile strength, yield strength, and hardness of the integral spiral finned tubes produced by our company are higher than those of the base tubes, i.e., the national standard boiler steel tubes No. 20 and 20G, while the elongation is reduced. The increased hardness enhances the wear resistance of the integral finned tubes, particularly the improved hardness of the fins, which is beneficial for resisting erosion by flue dust, addressing the severe wear issue in fluidized bed boilers due to high flue gas velocity and hard particles on the heating surfaces. The decrease in elongation, i.e., reduced plasticity, does not affect the use of the finned tubes since manufacturing economizers with finned tubes does not require tube bending (only end welding), and high plasticity is not necessary. In summary, integral finned tubes represent a new manufacturing method for spiral finned tubes and can be considered, within a certain range, the next-generation product replacing high-frequency welded and brazed spiral finned tubes. The integral finned tubes produced by our company have undergone comprehensive technical testing and evaluation by multiple relevant national agencies, meeting or exceeding the relevant regulations of the national steel tube standards for the boiler industry. In terms of the quality assurance system, the company strictly implements the established "Integral Spiral Finned Steel Tube Production Process Operating Procedures," including specifications for processing machinery and equipment, operational procedures, raw material procurement, and product inspection.