How To Choose The Right Boiler Tube Type for Boiler?

When choosing the right boiler tube for your boiler, you need to consider a number of key factors, including the boiler's operating pressure, temperature, medium characteristics, and the material, specifications, and corrosion resistance of the tube itself.

Working pressure factors

1. Low-pressure boilers (<1.6MPa)

For boilers with lower working pressures, such as some small industrial steam boilers or hot water boilers, carbon steel pipe can be used. Carbon steel has good mechanical properties and can meet the strength requirements under low pressure environments. For example, the common No. 20 carbon steel pipe is relatively cheap, easy to process and manufacture, and can stably transport steam or hot water within a low pressure range.

2. Medium-pressure boilers (1.6 - 10MPa)

When the boiler's working pressure is in the medium pressure range, alloy steel tubes are a more appropriate choice. The addition of alloying elements enhances the strength and toughness of the tube, enabling it to withstand higher pressures. For example, 15CrMoG alloy steel pipes contain chromium (Cr) and molybdenum (Mo) elements. These alloy elements improve the high temperature strength and creep resistance of the pipes, and perform well in the superheater and reheater pipes of medium pressure boilers.

3. High-pressure boilers (>10MPa)

High-pressure boilers require pipes with extremely high strength and good pressure resistance. At this time, pipes with higher alloy content, such as 12Cr1MoVG or P91 (9Cr - 1Mo - V - Nb) steel pipes, are usually selected. 12Cr1MoVG steel pipes have excellent comprehensive performance under high temperature and high pressure environments through the synergistic effect of alloy elements such as chromium (Cr), molybdenum (Mo) and vanadium (V); P91 steel pipes are widely used in supercritical and ultra-supercritical pressure boilers with their high strength, good steam oxidation resistance and thermal stability.

.

Working temperature factors

1. Low temperature (<300℃) boiler tubes

For boilers working in low temperature environments, such as some hot water supply boilers, the corrosion resistance and thermal conductivity of the pipes are mainly considered. Ordinary carbon steel pipes or stainless steel pipes can meet the requirements. Stainless steel pipes (such as 304 stainless steel) have good corrosion resistance. In low temperature hot water systems that may be exposed to slightly corrosive media, they can effectively prevent pipe corrosion and extend service life. At the same time, the thermal conductivity of stainless steel pipes can also meet the transportation needs of low temperature hot water.

2. Medium temperature (300 - 500℃) boiler tubes

For boilers with working temperatures in the medium temperature range, such as some medium temperature and medium pressure industrial steam boilers, alloy steel pipes are the first choice. Taking 12CrMoG as an example, the chromium (Cr) element in this pipe can improve the oxidation resistance of the pipe, and the molybdenum (Mo) element enhances the thermal strength of the pipe, so that it can stably transport steam in the temperature range of 300 - 500℃ and resist high temperature oxidation and thermal fatigue.

3. High temperature (>500℃) boiler tubes

In high temperature environments, such as superheaters and reheaters of supercritical and ultra-supercritical pressure boilers, tubes with excellent high temperature performance are required. Nickel-based alloy tubes (such as Inconel 617) are a good choice. Inconel 617 contains a large amount of elements such as nickel (Ni), chromium (Cr) and molybdenum (Mo), which make it have excellent high temperature corrosion resistance, creep resistance and oxidation resistance. It can work stably for a long time in a high temperature steam environment to ensure the efficient operation of the boiler.

Medium characteristic factors

1. Steam boiler tubes

If the boiler is mainly used to generate steam, the tubes need to have good steam transmission performance and resistance to steam oxidation. For general industrial steam boilers, medium alloy steel or high alloy steel is a common material. For example, T91 (9Cr - 1Mo - V - Nb) steel pipes can effectively resist steam oxidation in a high temperature steam environment, forming a dense oxide film to prevent further oxidation of the tubes. At the same time, its high strength and good thermal conductivity are conducive to the efficient transportation of steam.

2. Hot water boiler tubes

The medium of hot water boilers is hot water, and the corrosion resistance and thermal conductivity of the tubes are mainly considered. If the hot water contains a small amount of corrosive substances, such as chloride ions, stainless steel tubes (such as 316L stainless steel) are a better choice. 316L stainless steel contains molybdenum (Mo) elements, which enhances the tolerance to corrosive media such as chloride ions, and its thermal conductivity can meet the transportation requirements of hot water and ensure the stable operation of the hot water boiler system.

3. Special medium boiler tubes (such as corrosive gases or chemicals)

When the boiler medium contains corrosive gases (such as hydrogen sulfide, sulfur dioxide) or chemicals (such as acids and alkalis), it is necessary to select tubes with high corrosion resistance. For example, Hastelloy tubes have strong tolerance to various strong acids, strong alkalis and corrosive gases. Hastelloy C-276 contains elements such as chromium (Cr), molybdenum (Mo) and tungsten (W), which make it show excellent corrosion resistance in boiler environments containing corrosive media, which can effectively protect the tubes and extend their service life.

Comprehensive consideration of pipe material, specifications and corrosion resistance

1. Material selection

In addition to the above selection of materials based on pressure, temperature and medium characteristics, the cost and machinability of the pipe also need to be considered. Carbon steel has a low cost, but relatively weak corrosion resistance; alloy steel has a moderate cost and better performance; stainless steel and nickel-based alloys have a high cost, but excel in corrosion resistance and special properties. On the premise of meeting the performance requirements of the boiler, the most cost-effective material should be selected as much as possible.

2. Specification determination

The specifications (pipe diameter and wall thickness) of the pipe should be determined according to the flow requirements and pressure loss of the boiler. Generally speaking, the larger the pipe diameter, the greater the flow, but the wall thickness also needs to be increased accordingly to withstand the pressure. By calculating the steam or hot water flow, flow rate and allowable pressure loss of the boiler, the appropriate pipe diameter and wall thickness can be determined. For example, in the main steam pipeline of a large steam boiler, in order to ensure the rapid delivery of a large amount of steam, a larger pipe diameter pipe will be selected, and the appropriate wall thickness will be determined according to the pressure requirements.

3. Corrosion resistance considerations

Corrosion resistance is one of the key factors for the long-term stable operation of boiler tubes. In addition to choosing the right material, the corrosion resistance of the pipe can also be enhanced by surface treatment (such as coating). For some boiler tubes working in harsh corrosive environments, such as boilers at the seaside or in chemical companies, the use of anti-corrosion coatings (such as ceramic coatings) can further improve the corrosion resistance of the pipe and extend its service life.

Summary

Choosing the right type of boiler tube for the boiler is a complex process that takes into account multiple factors. Only by comprehensively considering the working pressure, temperature, medium characteristics of the boiler, as well as the material, specifications and corrosion resistance of the pipe, can the safe, efficient and stable operation of the boiler tube in the boiler system be ensured.