What Is DIN 17175?
DIN 17175 high-temperature seamless steel pipe is a German standard seamless steel pipe designed for high-temperature environments. Its carbon content is typically between 0.10% and 0.20%, a design that ensures the steel maintains both strength and toughness at elevated temperatures. The standard covered seamless tubes of carbon and low-alloy steel for boiler and plant construction, and although it has been withdrawn and largely superseded by the European standard EN 10216-2, the DIN 17175 grade designations such as St35.8 and St45.8 are still widely used in engineering practice and in legacy plant documentation.
Material Grades and Chemical Composition
DIN 17175 covered both non-alloy carbon grades and low-alloy creep-resistant grades. The main carbon grades are St35.8 and St45.8, while 15Mo3 adds molybdenum and 13CrMo44 adds chromium and molybdenum for higher temperature creep resistance.
| Grade | C (max) | Mn | Cr | Mo |
|---|---|---|---|---|
| St35.8 | 0.17% | 0.40 - 0.80% | - | - |
| St45.8 | 0.21% | 0.40 - 1.20% | - | - |
| 15Mo3 | 0.20% | 0.40 - 0.80% | - | 0.25 - 0.35% |
| 13CrMo44 | 0.18% | 0.40 - 1.00% | 0.70 - 1.10% | 0.40 - 0.50% |
In addition to carbon, the chemical composition includes elements such as silicon, manganese and, for the low-alloy grades, chromium and molybdenum. The chromium content of the alloyed grades, around 0.7% to 1.1% in 13CrMo44, helps enhance the steel's corrosion resistance and high-temperature strength.
Mechanical and High-Temperature Properties
DIN 17175 high-temperature seamless steel pipe exhibits excellent oxidation resistance. At temperatures up to 500-600°C it forms a dense oxide film on its surface, preventing further oxidation. Its thermal expansion coefficient is approximately 10 to 13 x 10-6/°C, providing relatively stable dimensional behaviour in high-temperature environments and adaptability to various thermal conditions. Its hardness generally ranges between HB 120 and 180, balancing machinability with resistance to wear and deformation at high temperatures. The pipe also exhibits good impact toughness, with an impact energy of typically 30-50 J at room temperature, allowing it to withstand certain impact loads without cracking. Compared with ordinary seamless steel pipes, DIN 17175 tubes demonstrate significantly improved creep resistance at high temperatures, maintaining stable shape and performance under prolonged high-temperature and high-pressure conditions. For example, the long-term creep strength of typical grades reaches approximately 100-150 MPa at 500°C, which meets the requirements for prolonged high-temperature operation.
Manufacturing and Dimensional Tolerances
The pipe is usually manufactured using hot rolling processes. After hot rolling, the outer diameter tolerance is controlled within plus or minus 1.0% to 1.5%, and the wall thickness tolerance is within plus or minus 5% to 10%, ensuring dimensional accuracy. In terms of welding, DIN 17175 high-temperature seamless steel pipe can be joined using various methods, including manual arc welding and TIG welding. Preheating and post-weld heat treatment are essential to ensure welding quality, particularly for the low-alloy grades.
Testing, Inspection and Applications
Tubes supplied to DIN 17175 were subject to a comprehensive testing programme, including tensile test, notch impact and bending tests, ring test, non-destructive test, visual inspection of the tube surface, gauging, leakage test, grade identification test and hot tensile test. These tests verify that the material meets the strength, toughness and soundness requirements for elevated temperature service. This type of pipe is commonly used in high-temperature components of power station boilers, such as superheaters and reheaters, where its long-term creep strength meets the requirements for prolonged high-temperature operation. It is also used in refinery furnaces, heat exchangers and general pressure piping where service temperatures exceed the capability of ordinary carbon steel tubing.
Frequently Asked Questions
What does DIN 17175 cover?
DIN 17175 covered seamless steel tubes of carbon and low-alloy steel for use at elevated temperatures, mainly in boiler and plant construction, with grades such as St35.8, St45.8, 15Mo3 and 13CrMo44.
Is DIN 17175 still current?
The standard has been withdrawn and is largely superseded by EN 10216-2, but the DIN grade designations and property data remain widely referenced in existing plants and engineering specifications.
What is the maximum service temperature?
The grades are designed for sustained service up to about 500-600°C, where they form a protective oxide film and retain useful creep strength.
Can DIN 17175 tubes be welded?
Yes. Manual arc welding and TIG welding are commonly used, with preheating and post-weld heat treatment essential, especially for the low-alloy grades.
What is the difference between St35.8 and St45.8?
Both are non-alloy carbon grades; St45.8 has a higher carbon and manganese content, giving it higher strength, while St35.8 offers better formability and weldability.