Boiler Tubes — Fire-tube & Water-tube (ST35.8 / P235GH)

Boiler tubes — known in the industry by the grade ST35.8 (per DIN 17175) and its modern equivalent P235GH (per EN 10216-2) — are used in demanding thermal applications such as steam boilers and pressure equipment. Thanks to their high resistance to temperature and pressure, they are among the most widely used materials in the power-generation and boiler-manufacturing industries.

Boiler tubes are supplied in two common arrangements: fire-tube and water-tube. (In the Iranian market both are traded under the single local term "آتشخوار / Atashkhar".)

Fire-tube and Water-tube

• Fire-tube: hot gases and flame pass through the inside of the tube, while water surrounds it.
• Water-tube: water passes through the inside of the tube, while hot gases flow around it.

The tube type is selected based on the boiler design and service conditions (temperature and pressure), not merely on dimensions.

Relation to Heat Exchanger Tubes

Boiler/fire tubes and heat exchanger tubes can share the same material (both are often supplied in ST35.8 or P235GH), but in industrial terms they are not identical. A boiler tube refers to boiler applications and high temperature/pressure service, whereas a heat exchanger tube is the heat-transfer element inside an exchanger. In some cases a single tube may serve both purposes. For technical details, see the Heat Exchanger Tube page.

Grade and Standard

The two grades are very close in application and composition; in practice P235GH is the updated equivalent of ST35.8.

Main Applications

• Steam boilers (fire-tube and water-tube)
• Superheaters and economizers
• Pressure equipment and vessels
• Power, refinery and petrochemical industries

Dimensions & Ordering

Dimensions and grades are supplied according to your request and order specifications. Contact MANIK TRADING for your required sizes and specifications.