How to select the appropriate stainless steel heat exchange tubes or stainless steel fluid tubes?

Select the appropriate stainless steel heat exchange tubes or stainless steel fluid tubes, taking into account the specific requirements of the working conditions (such as function, medium, temperature, pressure, etc.). A comprehensive assessment should be conducted from multiple dimensions including functional positioning, material properties, structural design, and standard specifications. Here is a step-by-step selection guide: 

1. Clearly define the core functional requirements (heat exchange tubes vs fluid tubes)

1. Prioritize the determination of the purpose

If used for heat exchange (such as heat exchangers, condensers): Select stainless steel heat exchange tubes, with a focus on "efficient heat transfer" and "temperature difference adaptability". 

If used for fluid transportation (such as in pipeline systems or medium transmission): Select stainless steel fluid pipes, and focus on "safe transportation" and "control of fluid resistance". 

II. Analysis of Operating Conditions and Environmental Parameters

1. Medium Characteristics

Corrosiveness:

General corrosive environments (such as water, weak acids): 304 stainless steel can be selected (low cost and balanced overall performance). 

Highly corrosive or chloride-containing environments (such as seawater, salt solutions): Choose 316L (resistant to chloride corrosion), or 2205 duplex steel (higher strength and corrosion resistance). 

High-temperature oxidation environment (such as flue gas, steam): Optional 321 (contains Ti, resistant to intergranular corrosion), 310S (resistant to high temperatures up to 1200℃), or nickel-based alloys (such as Inconel 625). 

Cleanliness:

For the food and pharmaceutical industries, "hygienic pipes" are required. Choose fluid pipes with polished inner walls (such as 316L, Ra ≤ 0.8μm); if the medium is prone to scaling in heat exchange pipes, select threaded pipes or corrugated pipes (to enhance turbulence and reduce scaling). 

2. Temperature and Pressure

High-temperature scenario (＞300℃): 

Heat exchange tubes: Preferentially select materials with high thermal conductivity and good high-temperature strength (for example, 304 has better thermal conductivity than 316L, but 321 is more resistant to high-temperature creep). 

Fluid pipe: Must meet the long-term strength under high temperatures (refer to the high-temperature steel grades in GB/T 14976 or ASME SA312). 

High-pressure scenarios (such as high-pressure boilers, chemical reactors): 

Heat exchange tubes: Must be thick-walled seamless tubes (such as those specified in GB/T 24593 for high-pressure heat exchange tubes), ensuring resistance to temperature difference stress and pressure resistance. 

Fluid pipe: Select the wall thickness based on the pressure rating (such as Sch40, Sch80), and conduct a hydraulic test (usually 1.5 times the working pressure). 

3. Flow Rate and Flow Volume 

Heat exchange tubes: With small diameters (such as φ19mm, φ25mm), they are easy to be arranged densely, thereby increasing the heat exchange area; special structures (such as fins / threads) enhance turbulence and strengthen heat transfer (suitable for gases or low-flow-rate liquids). 

Fluid pipe: The pipe diameter is calculated based on the flow rate (following the economic flow velocity: 1-3 m/s for liquids, 10-30 m/s for gases), and the inner wall is smooth to reduce pressure drop (avoid using structures with fins or threads). 

III. Material Grade Selection (Core Parameter Comparison)

(Attached Figure 1) 

IV. Structural Design and Specification Selection 

1. Special design of heat exchange tubes

Enhanced heat transfer structure:

Finned tubes: Used for gas-side heat exchange (increasing the surface area, such as air coolers); 

Threaded pipe / Bellows pipe: Increases fluid turbulence and reduces fouling (suitable for media prone to scaling, such as scale and oil deposits); 

Thin-walled tubes (with wall thickness ≤ 1mm): Reduce thermal resistance, but ensure pressure resistance (such as sealing during expansion / welding). 

Specification range: Outer diameter is usually 10 - 50mm. Length is customized according to the size of the heat exchanger (e.g. 3 - 12 meters). It needs to be compatible with the hole spacing and arrangement method of the tube plate (triangle / square arrangement). 

2. General Design of Fluid Pipes

Inner wall requirements: Smooth without burrs (Ra ≤ 3.2 μm), to reduce fluid resistance and scale formation; sanitary pipes need to be polished (Ra ≤ 0.8 μm). 

Connection method: Select the connection method based on pressure and pipe diameter. For example, welding (for high pressure), clamp (for sanitary grade), or thread (for small diameter and low pressure). Ensure the sealing performance (such as the expansion welding connection between heat exchange tubes and tube plates). 

Specification range: Outer diameter 6 - 1200mm. Wall thickness is selected according to ASME B36.19 or GB/T 17395 (such as Sch10S - Sch160S). 

V. Adhering to Industry Standards and Inspection Requirements

1. Key Standards for Heat Exchanger Tubes

Material Standards: GB/T 24593 (China's Seamless Heat Exchanger Tubes), ASTM A213 (American Standard Boilers and Heat Exchangers Tubes). 

Equipment standards: GB/T 151 (for heat exchanger design), ASME BPVC Section VIII Div.1 (for pressure vessels), and it must meet the mechanical properties of the tube sheet connection (such as expansion joint tensile force, welding inspection). 

Test items: Hydrostatic test (≥ 1.5 times the design pressure), eddy current inspection (for detecting internal defects), intergranular corrosion test (for sensitized materials). 

2. Key standards for fluid tubes

Material standards: GB/T 14976 (Chinese seamless tubes for fluid transportation), ASTM A312 (American standard welded / seamless austenitic tubes), EN 10217-7 (European standard corrosion-resistant steel tubes). 

Engineering standards: SH/T 3059 (Petroleum Pipeline Design), GB 50316 (Industrial Metal Pipeline Specification), and they must meet pressure - temperature grades (such as PN16, PN40). 

Test items: Tensile test (strength / elongation), compression test (resilience), air tightness test (for transporting hazardous media such as gas). 

VI. Other Key Factors

1. Cost and Supply Cycle

Heat exchange tubes: With special structures (finned / threaded) and using high-end materials (duplex steel / nickel-based alloys), the cost is relatively high and needs to be customized in advance; 

Fluid tubes: Standard optical tubes are available quickly. For large-diameter or thick-walled tubes, customization may be required. Note the negative deviation in wall thickness (which affects the pressure rating). 

2. Process Adaptability

Heat exchange tubes: The expansion/bonding / welding process needs to be considered (for example, for 316L welding, the heat input must be controlled to avoid intergranular corrosion); 

Fluid pipe: Processing capabilities such as bending and flaring (for example, the ductility of 304 is superior to duplex steel, making it easier to shape). 

3. Industry-specific requirements

Food and pharmaceuticals: Must obtain FDA certification; choose 316L sanitary tubes (with internal wall electro-polished finish); 

Nuclear power / Aerospace: Must meet strict cleanliness standards and undergo non-destructive testing (such as 100% radiographic inspection). 

VII. Summary of Decision-making Process

Clarified functions: Heat exchange → Select heat exchange tubes (focus on heat transfer structure); Transportation → Select fluid tubes (focus on pressure resistance and corrosion resistance). 

Analysis conditions: medium (corrosion / cleanliness), temperature / pressure, flow rate / velocity → select material grade (such as 316L, 2205). 

Design specification: Select the pipe diameter / wall thickness for the heat exchange tubes + the reinforcement structure (fin / thread); Select the pipe diameter / wall thickness for the fluid tubes + the connection method (welding / clamp). 

Follow the standard: Select manufacturing standards in accordance with industry norms (such as GB/T, ASME), and complete inspections (hydrostatic test / flaw detection / material re-inspection). 

Comprehensive assessment: Balance performance (thermal conductivity / strength), cost (conventional materials vs. special materials), and delivery cycle. If necessary, consult the manufacturer for a customized solution. 

Through the above steps, it is possible to systematically select the stainless steel pipes that meet the working conditions requirements, avoiding problems such as low efficiency, leakage or premature failure caused by improper selection.