DIN17175 St35.8 Seamless Tubes for Boilers

DIN 17175 St35.8 is a standardized seamless carbon steel tube specifically engineered for high-temperature and high-pressure applications in boilers, heat exchangers, and petrochemical equipment. Below is a detailed technical overview:

1. Material Composition & Properties

Chemical Composition :

Element	Content (%)
C	≤0.17
Si	0.10–0.35
Mn	0.40–0.80
P	≤0.040
S	≤0.040
Cr/Mo	Not required
Low carbon and controlled impurities ensure weldability and resistance to oxidation at high temperatures.

Mechanical Properties :

Property	Value
Yield Strength	≥235 MPa
Tensile Strength	360–480 MPa
Elongation	≥25%
Balanced strength and ductility suitable for dynamic thermal stresses.

2. Manufacturing & Specifications

Process: Produced via cold-drawn or hot-rolled methods, followed by heat treatments (annealing, stress-relieving) to enhance microstructural stability .

Dimensions:

Outer Diameter: 14–711 mm (commonly 25.4–720 mm)

Wall Thickness: 2–60 mm

Length: Fixed (6m, 9m, 12m) or custom (5–16m).

Tolerances:

OD: ±0.6% (cold-drawn) to ±0.9% (hot-rolled)
WT: +15%/-10% (thin walls) to ±10% (thick walls).

3. Key Applications

High-Pressure Boilers: Superheaters, economizers, reheater tubes in boilers operating at ≥9.8 MPa and 450–650°C .

Petrochemical & Power Engineering: Heat exchangers, pressure vessels, pipeline systems .

Limitations: Long-term use ≤450°C to avoid graphite formation (carbon steel degradation) .

4. Surface Treatment & Certification

Surface Finish: Oiling, varnish, phosphating, or black paint to prevent corrosion during storage/transport .

Quality Assurance: Mandatory non-destructive testing (ultrasonic, eddy current) and certifications (ISO 9001, PED) .

5. Equivalent Standards & Grades

Global Equivalents :

Region Standard Equivalent Grade

Europe EN 10216-2 P235GH

USA ASTM A106 Grade B

China GB 5310 20G

Critical Considerations

Temperature Sensitivity: Not recommended for >450°C long-term service due to graphitization risk .

Corrosion Resistance: Lacks alloying elements (Cr, Mo); unsuitable for highly corrosive environments unless coated .

Procurement: Suppliers like Kingmetal Steel (China) offer OEM customization with traceable material test reports .

Summary

DIN 17175 St35.8 seamless tubes provide cost-effective, weldable solutions for medium-temperature boiler components but require strict adherence to temperature limits and quality controls. For higher temperatures (e.g., 510–580°C), alloy grades like 15Mo3 or 13CrMo44 (also under DIN 17175) are preferable .