Which material is used for boiler tubes?

Boiler tubes are a piping system designed for use in high temperature and high pressure environments.

The main function of boiler tubes is to transport steam or other media, and to withstand the effects of harsh environments such as high temperature, high pressure, and water vapor corrosion. Boiler tubes can be both seamless pipe and welded pipe, with seamless tubes being more popular due to their higher pressure and temperature resistance. Its specifications are usually expressed in terms of outer diameter or side length and wall thickness, and range in size from very small capillary tubes to large diameter tubes of several meters in diameter.

Boiler tubes are widely used in industrial boilers, heat exchangers, power stations and other equipment, and are a very important component of these equipment. According to their high temperature performance, boiler tubes can be divided into ordinary boiler tubes and high-pressure boiler tubes. High-pressure boiler tubes are often exposed to high temperature and high pressure conditions, and are required to have high lasting strength, oxidation corrosion resistance and structural stability.

Boiler tube material requirements:

The materials used for boiler tubes must be carefully selected to meet the following requirements:
(1) High temperature resistance and high strength
High-pressure boiler tubes are often exposed to high temperature and high pressure conditions during use. Under the action of high-temperature flue gas and water vapor, pipelines will oxidize and corrode. Steel pipes are required to have high lasting strength, high oxidation resistance, corrosion resistance and good structural stability. The working conditions of high-pressure boiler tubes are very harsh. They must work safely under high pressure, high temperature, and the erosion and corrosion of high-speed airflow, water flow, and gas for 10 to 20 years, or even longer.

(2)Thermal conductivity
Boiler tubes, especially high-pressure boiler tubes, are pipes used to transport high-temperature and high-pressure steam or hot water and play an important role. In the design and use of high-temperature boiler tubes, thermal conductivity is a very critical indicator.

Thermal conduction is the process by which heat is transferred from a high-temperature object to a low-temperature object. In high-temperature boiler tubes, heat conduction occurs mainly through conduction in the tube wall. The heat conduction characteristics of the pipe wall are related to the thermal conductivity of the material, wall thickness, pipe diameter and temperature gradient.

(3) Comply with standards: Materials must comply with safety and quality standards set by regulatory agencies such as ASTM, ASME or EN.

Common ASTM standards for boiler tubes include:
ASTM A192/A192M: This is the standard specification for seamless carbon steel boiler tubes for high pressure applications.
ASTM A210/A210M: Covers standards for seamless medium carbon steel boiler tubes and boiler smoke tubes, including safety ends, vault and support tubes, and superheater tubes.
ASTM A213/A213M: Provides specifications for seamless ferritic and austenitic alloy steel boiler, superheater and heat exchanger tubes.
ASTM A335/A335M: Specifies the minimum and nominal wall thickness for seamless ferritic alloy steel boiler tubes suitable for high temperature service.
ASTM A450/A450M: Covers standards for minimum wall thickness, seamless carbon steel boiler and superheater tubes for high pressure applications.

ASTM A178 / ASME SA178 Resistance Welded Carbon Steel Boiler Tube
ASTM A178 Boiler and superheater tubes for electric welding of carbon steel and carbon manganese steel boiler and superheater tubes. ASTM A178 is the same as ASME SA-178 and is a standard specification covering minimum wall thickness resistance welded pipe for boiler tubes, boiler flues, superheater flues, and minimum wall thickness made of carbon steel and carbon manganese steel.

It offers three levels:
Grade A – Mild Steel (low carbon steel)
Grade C - medium carbon steel
Grade D - carbon manganese steel

ASME Standard Example: ASME SA192 Boiler Tube
SA192 is a material, specifically, it is a standard used for manufacturing high-pressure boiler tubes. This pipe performs well in high-pressure environments due to its excellent tensile strength and yield strength, as well as good elongation, and is able to withstand large pressures and stresses. The chemical composition of SA192 steel pipes is strictly controlled and mainly includes elements such as silicon, manganese, chromium, molybdenum, copper and nickel. The content of these elements has an important impact on the performance and quality of the pipe. In addition, SA192, together with SA-193 and SA-194, is classified as a standard for stainless steel, stainless iron or alloy steel.
  

Commonly used materials for boiler tubes:

Boiler tubes are usually made of carbon steel, stainless steel and alloy steel tubes. Their differences are shown in the table below.
 

Attribute	Carbon Steel Boiler Tubes	Stainless Steel Boiler Tubes	Alloy Steel Boiler Tubes
Chemical Composition	Iron and carbon, low carbon content (<0.35%)	At least 10.5% chromium, often with nickel, molybdenum	Iron, carbon, and various alloying elements (e.g., manganese, silicon, chromium, nickel)
Mechanical Properties	Lower strength and hardness	Good formability; moderate strength	Higher strength, toughness, and wear resistance
Corrosion Resistance	Low; may need coatings or linings	High due to chromium oxide layer	Good to excellent, depending on alloying elements
Applications	General-purpose, low to moderate temperature and pressure	Corrosive environments, food processing, chemical industry	High-temperature and high-pressure applications, such as in power stations
Cost and Economy	Lower initial cost; may require more maintenance	Higher initial cost; potentially lower lifecycle cost	Varies; can be more expensive due to alloy content
Environmental Impact and Sustainability	Regular maintenance may be needed	Recyclable; low maintenance	Varies; some alloys are highly recyclable
Lifespan	Shorter lifespan if not properly protected against corrosion	Longer lifespan due to self-healing properties and corrosion resistance	Long lifespan, especially in harsh environments; depends on alloy composition

 

Boiler tube components and materials used:

Boiler Component	Function Description	Typical Material Used
Water Wall Tubes	Main heat-receiving surface around the furnace.	Carbon Steel
Convection Tubes	Further heating of fluid in the convection area of the boiler.	Carbon Steel or Alloy Steel
Downcomer Tubes	Transport water from the steam drum to the downcomer.	Carbon Steel
Header (Collector)	Collects and distributes boiler water; not typically exposed to radiant heat.	Carbon Steel or Stainless Steel
Superheater Tubes	Heat saturated steam into superheated steam, improving steam quality.	Alloy Steel
Economizer Tubes	Use residual heat from exhaust gases to raise feedwater temperature.	Carbon Steel or Alloy Steel

Read more: Why are the pipes used in industrial boilers all seamless steel tubes? or Boiler tube size chart