DIN 17175 is one of the most frequently searched German steel specifications in the boiler tube trade, and it is also one of the most widely misunderstood. It is not a material grade in itself. It is a standard for seamless tubes of heat-resistant steels, and the material is defined by the grade inside it, such as St35.8, 15Mo3 or 13CrMo44. Understanding that distinction is the first step in ordering the right tube.
What Is DIN 17175?
DIN 17175 is a German industrial standard covering seamless steel tubes for elevated temperatures, written mainly for boiler heating surface tubes and similar high-pressure applications. The standard groups a family of carbon steel, molybdenum steel and chromium molybdenum steel grades, and it defines not only their chemistry and mechanical properties but also tolerances, surface quality and testing rules.
The service envelope described by the standard splits into two bands. Low and medium pressure boilers operate at pressures up to 5.88 MPa and temperatures up to 450°C, where carbon steel grades are normally sufficient. High pressure boilers work at 9.8 MPa and above with temperatures from 450°C to 650°C, and that range calls for the molybdenum and chromium molybdenum grades. The corresponding Chinese standard is GB 5310, and the American equivalents are the ASME SA210 and SA213 families.
DIN 17175 has been largely superseded by EN 10216-2 for new projects in Europe, but the old grade names remain in circulation because existing plants, spare part lists and drawing registers still refer to them.
DIN 17175 Grades and Their EN Equivalents
| DIN 17175 Grade | EN 10216-2 Equivalent | Steel Number | Type |
|---|---|---|---|
| St35.8 | P235GH | 1.0345 | Carbon steel |
| St45.8 | P265GH | 1.0425 | Carbon steel |
| 15Mo3 | 16Mo3 | 1.5415 | Molybdenum steel |
| 13CrMo44 | 13CrMo4-5 | 1.7335 | Chromium molybdenum steel |
| 10CrMo910 | 10CrMo9-10 | 1.7380 | Chromium molybdenum steel |
Chemical Composition of DIN 17175 Steels
| Grade | C | Si | Mn | P max | S max | Cr | Mo |
|---|---|---|---|---|---|---|---|
| St35.8 | 0.17 max | 0.10 – 0.35 | 0.40 – 0.80 | 0.040 | 0.040 | – | – |
| St45.8 | 0.21 max | 0.10 – 0.35 | 0.40 – 1.20 | 0.040 | 0.040 | – | – |
| 15Mo3 | 0.12 – 0.20 | 0.10 – 0.35 | 0.40 – 0.80 | 0.035 | 0.035 | – | 0.25 – 0.35 |
| 13CrMo44 | 0.10 – 0.18 | 0.10 – 0.35 | 0.40 – 0.70 | 0.035 | 0.035 | 0.70 – 1.10 | 0.45 – 0.65 |
| 10CrMo910 | 0.08 – 0.15 | 0.50 max | 0.40 – 0.70 | 0.035 | 0.035 | 2.00 – 2.50 | 0.90 – 1.10 |
Note that the molybdenum grades carry a single alloying addition, while the chromium molybdenum grades combine both elements to raise creep resistance further. The 10CrMo910 grade is the most heavily alloyed of the group, with roughly 2.25% chromium and 1% molybdenum, and it is the grade that carries the highest temperature duty in the list.
Mechanical Properties of DIN 17175 Tubes
| Grade | Yield Strength, min (MPa) | Tensile Strength (MPa) | Elongation, min (%) |
|---|---|---|---|
| St35.8 | 235 | 360 – 480 | 25 |
| St45.8 | 255 | 410 – 530 | 21 |
| 15Mo3 | 275 | 450 – 600 | 20 |
| 13CrMo44 | 290 | 440 – 590 | 20 |
| 10CrMo910 | 280 | 450 – 600 | 18 |
The pattern is characteristic of heat-resistant tubing: yield strength and tensile strength rise as alloy content increases, while the minimum elongation falls. St35.8 is the most ductile and the weakest, and 10CrMo910 is the least ductile of the group while offering the best elevated-temperature performance.
Tolerances, Surface Quality and Testing
Surface quality requirements are strict because the tubes form part of a pressure boundary. Tubes must be free from cracks, laminations and folds. Minor protrusions, depressions and shallow longitudinal rolling marks that stay inside the wall thickness tolerance are permitted, and defects may be ground away provided the minimum wall thickness is still met. The outer diameter may slightly exceed the negative deviation, but only over a short length.
Dimensional tolerances differ between hot finished and cold finished tubes. For hot finished tubes the outside diameter tolerance is ±0.75% up to 100 mm and ±0.9% from 100 to 320 mm, with a minimum absolute tolerance on the smaller sizes. Cold finished tubes are held to ±0.6% up to 120 mm with a tighter minimum. Wall thickness tolerances are expressed as a percentage of the standard wall thickness Sn defined in DIN 2448: +15% to −10% where the wall is below twice Sn, +12.5% to −10% between twice and four times Sn, and ±9% above four times Sn.
Each tube is subjected to a hydraulic pressure test or, as an alternative, to eddy current testing in place of the hydrostatic pressure test, with a hydraulic test pressure of 8 MPa. Grade III tubes additionally undergo longitudinal defect ultrasonic testing in accordance with the referenced test standard. Heat treatment may be normalizing, subcritical annealing, hardening and tempering with continuous cooling followed by tempering, or hardening and tempering with isothermal transformation, depending on the grade and the required properties.
DIN 17175 Steel: Frequently Asked Questions
Q: What is the material of DIN 17175 steel?
DIN 17175 is a standard, not a single material; it covers seamless heat-resistant boiler tubes in grades St35.8, St45.8, 15Mo3, 13CrMo44 and 10CrMo910.
Q: What is DIN 17175 equivalent to in the ASTM system?
The American equivalents are the ASME SA210 and SA213 families for boiler tube service, while GB 5310 is the corresponding Chinese standard.
Q: Is DIN 17175 still current?
The standard has been largely replaced by EN 10216-2 for new European projects, but its grade names are still widely used for spare parts and existing plant documentation.
Q: Which DIN 17175 grade is used for high pressure boilers?
The chromium molybdenum grades 13CrMo44 and 10CrMo910 are used for high pressure service at 9.8 MPa and above with temperatures of 450°C to 650°C.
Q: What is 10CrMo910?
It is the most highly alloyed grade in the standard, with about 2.25% chromium and 1% molybdenum, offering the best creep resistance of the group and an EN equivalent of 10CrMo9-10.
Q: How are DIN 17175 tubes tested?
Each tube receives a hydraulic pressure test or eddy current testing as an alternative, and grade III tubes also receive longitudinal defect ultrasonic testing.