Fire-tube Boiler Tube VS. Water-tube Boiler Tube

A boiler tube is a seamless steel tube specifically designed for use in the heating surface of a boiler, belonging to pressure piping components. Boiler tubes materials are typically include carbon steel or alloy steel, and their primary function is to efficiently transfer the heat energy generated by fuel combustion to water or steam, making them a core pressure-bearing component in the boiler system.

Boiler tubes can be categorized based on their application environment:

Fire-tube boiler tubes

Water-tube boiler tubes

The differences between the two lie not only in their structure but also in their heat transfer methods, pressure-bearing capacity, and application scenarios.

Fire-tube Boilers

1. Working Principle

The working principle of a fire-tube boiler is the combustion of coal, natural gas, oil, or biomass in the boiler's combustion chamber. The high-temperature gases produced by combustion then enter the boiler tubes and flow through a water-filled area. As the boiler tube temperature rises, the water in the combustion chamber generates steam, thus producing energy.

2. Features and Applications

This type of boiler is known for its simple structure and ease of maintenance, making it suitable for small to medium-sized industrial applications. However, a drawback of this simple design is its lower efficiency compared to water-tube boilers.

3. The Role of Boiler Tubes in Fire-tube Boilers

The boiler tubes in fire-tube boilers primarily function as heat transfer tubes. Common tube materials include ASTM A178, ASTM A192, and 20# steel, requiring good thermal conductivity and pressure resistance.

Water-tube Boilers

1. Working Principle

In contrast, water-tube boilers store water inside the boiler tubes. These tubes are connected to the combustion chamber, where water is directly converted into steam during combustion. The steam then enters the steam drum above the boiler, transferring energy to the boiler.

2. Features and Applications

Water-tube boilers offer higher thermal efficiency (typically 85%–90%), larger steam output, and faster heating, making them more suitable for high-pressure applications. Operators requiring large boiler systems for power generation, chemical processing, or other demanding processes typically choose water-tube boilers.

3. The Role of Boiler Tubes in Water-tube Boilers

Water-tube boilers use tubes that withstand higher pressure and temperatures, typically made of high-strength alloy materials such as ASTM A210, A213 T11/T22, 15CrMoG, and 12Cr1MoVG, which possess characteristics of high temperature resistance, oxidation resistance, and creep resistance.

Fire-tube Boilers VS. Water-tube Boilers: Advantages and Disadvantages

1. Advantages of Fire-tube Boilers

Simple design; Easy maintenance and repair; Lower initial costs; Higher water consumption per horsepower.

2. Advantages of Water-tube Boilers

Smaller footprint at rated output power; Greater steam output capacity; Ability to install internal/integral superheaters; Higher operating pressure range (1,000 PSIG+).

3. Disadvantages of Fire-tube Boilers

Lower capacity (typically up to 2,500 hp or 86,250 lb/h);

Lower operating pressure range (typically <350 PSIG);

Larger footprint at rated output power;

Longer start-up time.

4. Disadvantages of Water-tube Boilers

Lower water volume required per boiler horsepower;

Higher maintenance costs;

More stringent water quality requirements;

Higher initial purchase cost.

Fire-tube Boiler Tubes VS. Water-tube Boiler Tubes

Main Causes of Boiler Tube Failure

Boiler tubes are prone to damage during long-term operation under high temperature, high pressure, and corrosive environments. Common causes of failure include:

1. Fire-tube Boiler Tube Tailure

Metal overheating and cracking: Due to scale buildup or poor water circulation.

Corrosion and thermal fatigue: Improper water treatment, excessive oxygen content.

Tube end cracks: Improper installation, tube end protruding beyond the tube sheet.

2. Water-tube Boiler Tube Failure

Thermal shock rupture: Caused by excessively rapid boiler start-up or uneven flame distribution.

Scale shedding: Caused by localized overheating due to contamination inside and outside the tubes.

Corrosion fatigue: Caused by high oxygen content in the feedwater or improper pH control.

3. Preventive Measures

Select boiler tube materials that meet international standards (e.g., ASTM A210 / GB5310 / EN10216-2).

Strictly control feedwater quality (pH, hardness, conductivity).

Perform regular ultrasonic testing and hydrostatic testing.

Maintain stable combustion and avoid thermal stress.

FAQ

1. Which is More Energy-Efficient, A Fire-Tube Boiler Or A Water-Tube Boiler?

Water-tube boilers have higher thermal efficiency (up to 90%), but higher initial costs; 

Fire-tube boilers are more economical and suitable for small to medium-sized projects.

2. How Often Should Boiler Tubes Be Replaced?

Generally, they need to be inspected after 5–10 years of operation. The replacement cycle depends on water quality, operating pressure, and tube material grade.

Summary

Fire-tube boiler tubes are suitable for medium and low-pressure thermal energy systems and have economic advantages; water-tube boiler tubes are used in high-temperature and high-pressure environments and can better meet the needs of high energy efficiency and industrial-grade steam.