Product Description
ASTM A376 Tp347h/304 Fin Tube
1. Introduction
ASTM A376 is a standard that pertains to seamless and welded austenitic stainless steel tubes for high - temperature central - station service. Tp347h and Tp304 are two common grades within this standard, often fabricated into fin tubes. Fin tubes are designed to enhance heat transfer efficiency in various applications, such as heat exchangers. The difference in chemical composition between Tp347h and Tp304 leads to distinct mechanical and corrosion - resistant properties, making each suitable for specific operating conditions.
2. Chemical Composition
The chemical composition is a key determinant of the properties of these fin tubes. Table 1 shows the typical chemical composition ranges:
|
Element
|
Content in Tp304 (%)
|
Content in Tp347h (%)
|
|
Carbon (C)
|
≤0.08
|
0.04 - 0.10
|
|
Silicon (Si)
|
≤1.00
|
≤1.00
|
|
Manganese (Mn)
|
≤2.00
|
≤2.00
|
|
Phosphorus (P)
|
≤0.045
|
≤0.045
|
|
Sulfur (S)
|
≤0.030
|
≤0.030
|
|
Chromium (Cr)
|
18.0 - 20.0
|
17.0 - 19.0
|
|
Nickel (Ni)
|
8.0 - 10.5
|
9.0 - 13.0
|
|
Niobium + Tantalum (Nb + Ta)
|
-
|
8 x C - 1.00
|
In Tp304, chromium forms a passive oxide layer on the surface, providing basic corrosion resistance, and nickel enhances toughness and ductility. Tp347h, with the addition of niobium (Nb) (in the form of Nb + Ta), has improved resistance to sensitization and intergranular corrosion at elevated temperatures. The higher carbon content in Tp347h compared to Tp304 also affects its high - temperature strength.
3. Mechanical Properties
The mechanical properties of ASTM A376 Tp347h/304 fin tubes are crucial for their applications. Table 2 shows the typical mechanical properties:
|
Property
|
Value for Tp304
|
Value for Tp347h
|
|
Yield Strength (MPa) at Room Temperature
|
≥205
|
≥205
|
|
Tensile Strength (MPa) at Room Temperature
|
515 - 795
|
515 - 795
|
|
Elongation (%) at Room Temperature
|
≥40
|
≥35
|
|
Hardness (HB)
|
≤201
|
≤201
|
At elevated temperatures, Tp347h generally shows better creep - rupture strength due to its alloying elements, especially niobium. This makes it more suitable for applications where the fin tubes are exposed to high - temperature and high - stress conditions over long periods. Tp304, while having good general mechanical properties, may not perform as well as Tp347h under such extreme high - temperature loading.
4. Corrosion Resistance
4.1 General Corrosion Resistance
Tp304 fin tubes exhibit good general corrosion resistance in a wide range of environments, including atmospheric conditions, many organic and inorganic chemicals, and some mild acids. The passive oxide layer formed by chromium protects the surface from uniform corrosion. Tp347h also has good general corrosion resistance, and its resistance to intergranular corrosion is enhanced, especially in the temperature range where sensitization can occur (425 - 815°C). This makes Tp347h more suitable for applications where the fin tubes may be exposed to environments that could cause intergranular corrosion, such as certain chemical processing streams.
4.2 Oxidation Resistance at High Temperatures
Tp347h fin tubes are designed for high - temperature applications and have better oxidation resistance compared to Tp304 at elevated temperatures. The presence of niobium in Tp347h helps to form a more stable and protective oxide layer, which can withstand higher temperatures for longer periods without significant degradation. Tp304 can be used at moderately high temperatures but may experience more rapid oxidation and loss of mechanical properties at very high temperatures compared to Tp347h.
5. Manufacturing Process
5.1 Tube Manufacturing
- Seamless Process: For both Tp304 and Tp347h, a seamless process can be used. A solid billet is heated and pierced to form a hollow shell. Then, the shell is further processed by rolling or drawing to achieve the desired outer diameter and wall thickness. This process results in a tube with a uniform microstructure and good mechanical properties.
- Welded Process: Stainless - steel sheets or coils can be formed into a tubular shape and then welded. The welding process needs to be carefully controlled to ensure the integrity of the weld joint and maintain the corrosion - resistant and mechanical properties of the alloy. After welding, the tubes may undergo heat treatment to relieve welding stresses.
5.2 Fin Attachment
- Extrusion Method: In this method, fins are extruded directly from the base tube material. This results in a strong bond between the fins and the tube, ensuring efficient heat transfer. The extrusion process can be precisely controlled to achieve the desired fin shape and dimensions.
- Welding Method: Fins can be welded to the tube surface. This method offers flexibility in terms of fin material selection and can be used for a variety of fin shapes. However, the welding process needs to be carefully executed to ensure a good bond and avoid any negative impact on the corrosion resistance of the tube - fin assembly.
6. Applications
6.1 Power Generation
- Steam Generators: Tp347h fin tubes are widely used in steam generators in power plants. Their high - temperature strength and oxidation resistance make them suitable for withstanding the harsh conditions inside the steam - generating units, where high - temperature steam is produced. Tp304 fin tubes can also be used in some less - demanding steam - generation applications or in components where the temperature is not extremely high.
- Heat Exchangers: In power plant heat exchangers, both Tp304 and Tp347h fin tubes can be used. Tp304 may be used in heat exchangers for pre - heating or cooling processes where the temperature and corrosion conditions are relatively mild. Tp347h is preferred in high - temperature heat exchangers, such as those in superheater sections, where its superior high - temperature properties are crucial.
6.2 Chemical Processing Industry
- Reactor Heat Exchangers: Tp347h fin tubes are often used in reactor heat exchangers in chemical plants. They can resist the high - temperature and corrosive environment associated with chemical reactions. Tp304 fin tubes may be used in heat exchangers for less - corrosive chemical processes or in applications where the temperature is not as high.
- Distillation Columns: In distillation columns, fin tubes help to enhance heat transfer efficiency. Tp304 can be used in columns where the distillate is relatively non - corrosive and the operating temperature is moderate. Tp347h may be required in columns handling more corrosive substances or operating at higher temperatures.
6.3 Petroleum Refining
- Furnace Tubes: Tp347h fin tubes are commonly used in furnace tubes in refineries. They can withstand the high - temperature and high - stress conditions in the furnace, where hydrocarbons are processed. Tp304 fin tubes may be used in some auxiliary heating or cooling systems within the refinery where the temperature and corrosion requirements are less severe.
7. Conclusion
ASTM A376 Tp347h/304 fin tubes are important components in various industries due to their heat - transfer - enhancing design and good mechanical and corrosion - resistant properties. Tp304 offers a good balance of cost - effectiveness and performance for applications with moderate temperature and corrosion requirements. Tp347h, with its enhanced high - temperature strength and oxidation resistance, is specifically designed for more demanding high - temperature applications. As industries continue to seek more efficient heat - transfer solutions and materials that can withstand harsh operating conditions, these fin tubes are likely to remain in high demand, with continuous improvements in their manufacturing processes and performance.
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