What are DSS Low Fin Straight Tubes?
DSS Low Fin Straight Tube is a high efficiency heat transfer tube manufactured from duplex stainless steel (DSS) material, with dense but low-height spiral fins cold rolled onto the outer wall of the straight tube, while both ends remain plain (unfinned).
Since the fins and the base tube are integrally formed from the same material, there is no gap between them. This completely eliminates contact thermal resistance, ensuring continuity and high efficiency of the heat transfer path.
DSS Low Fin Straight Tubes
1. Material: DSS (Duplex Stainless Steel) -Why use DSS?
Ordinary low fin tubes may use carbon steel or 304/316L stainless steel. However, explicit designation of DSS (such as grades 2205, 2507, etc.) indicates that these tubes are specifically intended for harsh environments involving high corrosion and high stress.
| Element | UNS S31803 | UNS S32205 | UNS S32750 |
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| C | |||
| Mn | |||
| P | |||
| S | |||
| Si | |||
| Cr | |||
| Ni | |||
| Mo | |||
| N | |||
| Cu |
The yield strength of duplex stainless steel is approximately twice that of 304 stainless steel. Under the same operating conditions, thinner walls can be utilized, enabling equipment lightweighting, reducing material costs, and enhancing structural stability.
Duplex stainless steel combines the toughness of austenitic stainless steel with the high strength of ferritic stainless steel. It offers exceptional resistance to chloride induced stress corrosion cracking, which is crucial in environments such as seawater cooling and chemical processes containing chloride ions.
High Strength
Yield strength twice that of 304 stainless steel, enabling thinner wall design
Stress Corrosion Resistance
Superior resistance to chloride induced stress corrosion cracking
Good Comprehensive Mechanical Properties
Combines toughness of austenitic and strength of ferritic stainless steel
2. Type: Low Fin
Fins are formed on the outer wall of the tube via cold rolling, creating low-height spiral protrusions.
Although the fins are low in height, they significantly increase the external heat transfer surface area. Within a tube bundle, this allows for more efficient heat transfer between the fluids inside and outside the tubes. Because they are integrally rolled, there is no contact resistance, and the mechanical strength remains high.
3. Form: Straight Tube
Distinction from U-bend low fin tubes:
Emphasizing "straight tube" means it is supplied in standard straight lengths, typically with plain ends (without fins) for insertion into tubesheets for expansion or welding.
Manufacturing Process of DSS Low Fin Straight Tubes
The production of DSS low fin tubes primarily utilizes the cold rolling (cold roll forming) process:
Raw Material Preparation
Precision rolled seamless or welded duplex stainless steel tubes are selected as the base material (parent tube), with strict control over dimensional accuracy and metallurgical quality.
Plastic Forming
On specialized machinery, multiple sets of forming rolls with specific tooth profiles radially cold extrude the tube wall. During the rotating and axial feeding motion of the rolls, the metal on the outer surface undergoes plastic flow, being displaced into the gaps of the roll teeth, thereby forming continuous, smooth spiral fins.
Metal Flow Line Integrity
The cold rolling process ensures the metal grain flow lines follow the contour of the fin continuously without being cut. Consequently, the fins possess high mechanical strength and resistance to vibration fatigue.
Quality Inspection
After forming, dimensional checks, eddy current testing, and hydrostatic testing are typically performed to ensure the integrity and leak tightness of the tubes.
Advantages of DSS Low Fin Straight Tubes
Extremely High Heat Transfer Efficiency
Integral forming eliminates contact resistance, dense fins increase surface area and promote turbulence, fin structure improves phase change heat transfer coefficients for condensation/evaporation.
Compact Design
Reduces required tube bundle length or number of tubes for the same thermal duty, leading to smaller, lighter heat exchangers and lower capital investment.
Excellent Mechanical Strength
Integral fin structure resists damage during transport, installation and cleaning, making maintenance easier with high mechanical strength and vibration fatigue resistance.
Anti-Fouling and Easy Cleaning
Low height, moderate interfin spacing and smooth surface provide self-cleaning action; light fouling can be easily removed via chemical or mechanical cleaning.
Typical Application Areas
DSS Low Fin Straight Tubes are widely applied in various industrial fields due to their excellent corrosion resistance, high heat transfer efficiency and mechanical strength, the main application areas are as follows:
Petrochemical Industry: Widely used in column reboilers, overhead condensers, and compressor intercoolers, especially when handling corrosive media containing sulfur or chlorides where the DSS material offers significant advantages.
Marine Engineering: Utilized in shipboard seawater coolers and offshore platform process heat exchangers, leveraging the excellent seawater corrosion resistance of duplex stainless steel.
Power Industry: Employed in lube oil coolers, sample coolers, and various auxiliary cooling systems in nuclear and thermal power plants.
Chemical Processes: Serves as a core heat transfer component in evaporation, condensation, and heating processes involving highly corrosive media.
Pharmaceutical & Food Industries: In applications requiring high cleanliness, the use of DSS material balances corrosion resistance with hygienic requirements.