The high-pressure heat exchanger tube is responsible for the heat exchange between the heating steam and the boiler feed water and also withstands the high pressure of the boiler feed water. If the material of the heat exchanger tube is improperly selected, leakages of the heat exchanger tube are more likely to occur. Once a leakage is found in a heat exchanger tube, it must be shut down immediately. Otherwise, the heat exchanger tubes around the leaking tube will be continuously damaged, causing more and more leaked heat exchanger tubes. After the high-pressure heat exchanger tube is out of service, the power generation load of the unit will drop by 10% to 15%, seriously affecting the power generation efficiency of the unit. Therefore, the selection of heat exchanger tube materials is a very important issue.
 
1. Commonly used heat exchanger tube materials
According to domestic and foreign requirements for high-pressure heat exchanger tube materials, heat exchanger tubes are usually made from carbon steel, low alloy steel, and stainless steel. Copper tubes were also used in the early days, but copper tubes have low strength and poor high-temperature performance; they are no longer used in high-pressure heat exchanger tubes.
 
1.1 Carbon steel high-pressure heater heat exchanger tubes
The grades used for carbon steel high-pressure heater heat exchanger tubes play a crucial role in the overall performance and durability of these components. Carbon steel is a popular choice for heat exchanger tubes due to its excellent thermal conductivity, cost-effectiveness, and availability.

One commonly used grade is ASTM A179, which is a seamless carbon steel tube specifically designed for high-pressure applications. This grade offers good corrosion resistance and can withstand high temperatures without deformation or failure. It is also known for its excellent thermal conductivity, allowing efficient heat transfer between the hot and cold fluids. Another widely utilized grade is ASTM A192, which has similar properties to ASTM A179 but with higher tensile strength. This makes it suitable for even more demanding high-pressure environments. Additionally, ASTM A192 tubes are often used in power generation plants due to their ability to handle superheated steam. ASTM A210 is another important grade that finds application in high-pressure heater heat exchanger tubes. It offers superior mechanical properties compared to both ASTM A179 and ASTM A192 grades. This makes it ideal for extreme temperature conditions where other grades may fail.
 
Alloy steel high-pressure heat exchanger tubes
The grades used for alloy steel high-pressure heat exchanger tubes play a crucial role in determining the overall performance and durability of these tubes. Alloy steel is a type of steel that contains additional elements such as chromium, nickel, or molybdenum to enhance its mechanical properties. These additional elements improve the strength, corrosion resistance, and heat resistance of the alloy steel tubes. ASTM A213 T11, T12 and T22 are used for alloy steel high-pressure heat exchanger tubes. Cr and Mo are added for ASTM A213 T11, T12 and T22. Cr can increase the hardenability of steel and have the effect of secondary strengthening. After adding Cr, the material has good high-temperature oxidation resistance and oxidation resistance, which increases the thermal strength of steel. The addition of Mo can improve the oxidation resistance of the material. Therefore, ASTM A213 T11, T12 and T22 have better anti-scouring and anti-oxidation properties. ASTM A213 T91 is another important grade for alloy steel high-pressure heat exchanger tubes. It contains 9% chromium and 1% molybdenum, making it highly resistant to oxidation at high temperatures. This grade is ideal for applications involving extreme temperature conditions.
 
Selecting the appropriate grades for alloy steel high-pressure heat exchanger tubes is essential to ensure their optimal performance under extreme conditions. The choice of grade depends on factors such as operating temperature, pressure, corrosion resistance requirements, and mechanical properties needed for specific applications.
 
1.3 Stainless steel high-pressure heat exchanger tubes
Stainless steel high-pressure heat exchanger tubes play a crucial role in transferring heat efficiently and safely, making them an integral component of many industrial processes. The most common grades used include 304, 316, and 321 stainless steel.
 
Grade 304 stainless steel is the most commonly used grade for heat exchanger tubes due to its excellent corrosion resistance properties. It can withstand a wide range of corrosive environments, including acids and alkalis. Additionally, it offers good mechanical properties and is easily fabricated. Grade 316 stainless steel is another popular choice for high-pressure heat exchanger tubes. It contains molybdenum, which enhances its corrosion resistance in chloride environments such as seawater or brine solutions. This grade is also known for its excellent weldability and formability. Grade 321 stainless steel is preferred when the application involves elevated temperatures. It contains titanium, which stabilizes the structure against chromium carbide precipitation during welding or exposure to high temperatures. This grade offers excellent oxidation resistance up to 900°C (1652°F).
 
In conclusion, selecting the appropriate grade for stainless steel high-pressure heat exchanger tubes depends on the specific requirements of the application. Factors such as corrosion resistance, temperature stability, weldability, and formability must be carefully considered to ensure optimal performance and longevity of these essential components in industrial processes.
 
TP304, TP304L, TP304N, TP316 and TP316L are all austenitic stainless steels with good corrosion resistance, scouring resistance and oxidation resistance. When the carbon content of TP304L and TP316L is less than or equal to 0.03%, the single austenite structure is very stable and can be used in various temperature ranges with good corrosion resistance. When the carbon content of TP304, TP304N and TP316 stainless steel is greater than 0.03%, it exceeds the dissolved carbon content of austenite, which reduces the corrosion resistance to a certain extent and easily leads to intergranular corrosion, pitting corrosion and intergranular stress corrosion cracking. Therefore, austenitic stainless steels are all subjected to solution heat treatment to obtain a single austenite structure. The carbon content of 304L and 316L is low; the remaining carbon equivalent is less, and the single austenite structure is more stable. Therefore, the material has better corrosion resistance. When austenitic stainless steel stays at temperatures between 450 and 850°C, the carbon in the material will combine with chromium to form chromium carbide, which will deplete chromium between the crystals and cause intergranular corrosion. This is the sensitization of austenitic stainless steel. Austenitic stainless steel is also more sensitive to chloride ions and has poor chloride ion corrosion resistance.