DIN 1629 Seamless Steel Tubes for Pressure Purposes
Overview
DIN 1629 is the German Industrial Standard for seamless circular steel tubes for pressure purposes. It covers carbon and low-alloy steel tubes used for the conveyance of fluids and gases under pressure, particularly in applications requiring good weldability and formability. This standard has been largely superseded by EN 10216-2 but remains in use for some legacy applications.
Historical Context & Current Status
Transition Timeline:
DIN 1629 (1984 Edition): Original German national standard
Replaced by: EN 10216-2 (from 2002 onwards)
Current Use: Primarily for legacy systems, some specific German industrial applications
Relationship with EN Standards:
text
DIN 1629 Part 1 → EN 10216-2 (Non-alloy & alloy steel tubes) DIN 1629 Part 2 → EN 10216-3 (Alloy fine grain steel tubes) DIN 1629 Part 3 → EN 10216-4 (Austenitic stainless steel tubes)
Material Grades & Designations
DIN 1629 Part 1 (Carbon & Low-Alloy Steels):
| Old DIN Designation | Equivalent EN 10216-2 Grade | Minimum Yield (MPa) | Key Characteristics |
|---|---|---|---|
| St 35.0 | P195TR2 | 195 | General carbon steel, good weldability |
| St 35.4 | P235TR2 | 235 | Common carbon steel for moderate pressure |
| St 37.0 | - | 225 | Older grade, replaced by St 35.4 |
| St 45.0 | P265TR2 | 255 | Higher strength carbon steel |
| St 45.4 | - | 255 | Elevated temperature version |
| St 52.0 | P355TR2 | 355 | High strength, good toughness |
| 19Mn5 | - | 355 | Manganese steel, good toughness |
Nomenclature:
St = Steel ("Stahl" in German)
First Number = Minimum tensile strength in kg/mm² (approximate)
Second Number = Quality level (0=basic, 4=elevated temp properties)
Mechanical Properties (Example: St 35.4)
| Property | Room Temperature | Elevated Temperature (up to 300°C) |
|---|---|---|
| Yield Strength (ReH) | ≥ 235 MPa | ≥ 186 MPa |
| Tensile Strength (Rm) | 360-510 MPa | - |
| Elongation (A) | ≥ 25% | - |
| Bend Test | Mandatory (specific radius) | - |
Note: Properties vary by grade and part number.
Chemical Composition (Maximum %, Example: St 35.4)
| Element | St 35.4 | St 45.4 | St 52.0 |
|---|---|---|---|
| Carbon (C) | 0.17 | 0.21 | 0.22 |
| Silicon (Si) | 0.35 | 0.35 | 0.55 |
| Manganese (Mn) | 0.80 | 0.80 | 1.60 |
| Phosphorus (P) | 0.035 | 0.035 | 0.035 |
| Sulfur (S) | 0.035 | 0.035 | 0.035 |
| Aluminum (Al) | ≥ 0.020 | ≥ 0.020 | ≥ 0.020 |
All grades are fine-grain killed steel with aluminum treatment for grain refinement.
Manufacturing Process
Production Method:
Steel Making: Basic oxygen or electric arc furnace
Deoxidation: Fully killed steel with aluminum addition
Hot Working: Typically Mannesmann plug mill process
Heat Treatment: Usually normalized for Part 1 materials
Testing: Mandatory hydrostatic and mechanical testing
Size Range:
Outside Diameter: 21.3 mm to 610 mm (≈ ½" to 24")
Wall Thickness: 2.0 mm to 40.0 mm
Length: Typically 6-12m; up to 18m possible
Testing Requirements
| Test | DIN Standard Reference | Key Requirements |
|---|---|---|
| Hydrostatic Test | DIN 1629 Section 6 | Pressure = 20×S×tDD20×S×t (bar) Where S = 0.8 × ReH Duration ≥ 10 seconds |
| Tensile Test | DIN 50125 | One per heat, transverse specimens for D ≥ 40mm |
| Flattening Test | DIN 50136 | For D ≤ 50mm, flatten to specified distance |
| Bend Test | DIN 50111 | Alternative to flattening test |
| Hardness Test | DIN 50150 | Optional, by agreement |
| Nondestructive Test | Optional | Ultrasonic or eddy current |
Dimensional Tolerances
| Dimension | Tolerance per DIN 1629 | Comparison to Modern EN |
|---|---|---|
| Outside Diameter | For D ≤ 50mm: ±0.5mm For D > 50mm: ±1.0% |
Similar to EN 10216 |
| Wall Thickness | +15%, -10% of nominal | Slightly wider than modern EN |
| Eccentricity | ≤ 10% of nominal wall | Less strict than modern standards |
| Length | +10mm, 0mm for fixed length | Standard for that period |
| Straightness | ≤ 0.15% of length | Similar to current standards |
Applications
Traditional Uses (Legacy Systems):
German Industrial Plants: Pre-2000 installations
Power Generation: Moderate temperature steam systems
Chemical Industry: Process piping in older facilities
Heating Systems: High-temperature hot water
Industrial Gas: Compressed air and gas lines
Typical Service Conditions:
Temperature: Up to 300°C (for TR grades)
Pressure: Moderate to high pressure systems
Media: Steam, water, air, non-corrosive gases
Environment: Indoor industrial applications
Comparison with Modern EN Standards
| Aspect | DIN 1629 (Legacy) | EN 10216-2 (Current) |
|---|---|---|
| Standard System | German national standard | European harmonized standard |
| Grade Designation | St XX.X system | PXXXTRX system |
| Traceability | Basic heat traceability | Full EN 10204 certification |
| NDT Requirements | Optional | Often mandatory for critical applications |
| CE Marking | Not applicable | Required for PED applications |
| International Acceptance | Limited to German sphere | Worldwide acceptance |
Advantages & Limitations
Advantages:
Proven Performance: Decades of successful application
Good Weldability: Aluminum-killed fine grain structure
Formability: Suitable for bending and forming
Compatibility: With older German-designed systems
Limitations:
Obsolete: Replaced by EN standards
Limited Availability: Mills prefer producing to EN standards
Documentation: May not meet modern project requirements
Code Compliance: May not be accepted for new construction
Material Certification
Typical Documentation:
DIN 50049 3.1.B Certificate: With chemical and mechanical tests
Limited Traceability: Usually to melt/heat only
Language: Typically German, sometimes with English translation
Marking Requirements:
Manufacturer's identification
DIN 1629 designation
Grade (e.g., St 35.4)
Size (D × s)
Heat number
Inspector's mark
Fabrication & Welding
Welding Characteristics:
Preheat: Generally not required for thin sections
Filler Metals: AWS ER70S-6 or equivalent suitable
Post-Weld Heat Treatment: Optional for stress relief
Weldability: Excellent due to fine grain structure
Forming & Bending:
Cold Bending: Suitable for moderate radii
Hot Bending: Recommended for tight radii
Minimum Bend Radius: Typically 3× OD for cold bending
Ordering Information (Legacy Context)
Specification Format:
text
Seamless steel tubes to DIN 1629 Part 1 Grade: St 35.4 Dimensions: D [mm] × s [mm] × L [mm] Quantity: [number of pieces or meters] Additional requirements: [if any]
Sample Order (Historical):
text
DIN 1629 Part 1 - St 35.4 114.3 × 6.3 × 7000 mm Quantity: 50 pieces Test certificate: DIN 50049 3.1.B Hydrostatic test: 150 bar minimum
Migration to EN Standards
Conversion Guidelines:
| DIN 1629 Grade | Replace with EN 10216-2 Grade | Notes |
|---|---|---|
| St 35.0 | P195TR2 | Similar properties, better documentation |
| St 35.4 | P235TR2 | Direct equivalent |
| St 45.0 | P265TR2 | Higher strength available |
| St 45.4 | P265TR2 | Similar elevated temp properties |
| St 52.0 | P355TR2 | Similar strength level |
Benefits of Migration:
Modern Documentation: EN 10204 3.1/3.2 certificates
Global Acceptance: Recognized worldwide
PED Compliance: Essential for European pressure equipment
Better Availability: Mills stock EN grades
Improved Traceability: Full material history
Industry Usage Today
Where DIN 1629 Still Appears:
Spare Parts: For existing systems installed pre-2000
Plant Modifications: Where matching existing material is critical
German Legacy Equipment: Replacement parts for older machinery
Historical Documentation: Drawings and specifications from older projects
Procurement Challenges:
Limited Suppliers: Few mills produce to obsolete standards
Lead Time: Often requires special production runs
Cost Premium: Higher due to non-standard production
Quality Assurance: May not meet modern project QA requirements
Equivalent Standards Comparison
| Standard | Region | Status | Common Grades |
|---|---|---|---|
| DIN 1629 | Germany | Obsolete | St 35.4, St 45.4 |
| EN 10216-2 | Europe | Current | P235TR2, P265TR2 |
| ASTM A106 | USA | Current | Grade B |
| JIS G3454 | Japan | Current | STPG 410 |
Technical Summary
DIN 1629 represents a generation of German seamless pressure tube standards that served industry well for decades. Its material grades provided reliable performance for moderate temperature and pressure applications.
Key Technical Features:
Fine Grain Structure: Aluminum-killed steel for good toughness
Good Weldability: Suitable for most welding processes
Moderate Strength: Adequate for many industrial applications
Elevated Temperature Grades: TR variants for service up to 300°C
Modern Perspective:
While technically adequate for many applications, DIN 1629 is obsolete and should be replaced with EN 10216-2 equivalents for all new projects. The migration provides:
Better quality assurance
Modern documentation
Regulatory compliance
Global supply chain support
For existing installations, material testing and engineering assessment should determine if EN 10216-2 materials can be used as replacements, or if special production of DIN 1629 material is necessary for compatibility.
Recommendations
New Projects: Always specify EN 10216-2 instead of DIN 1629
Existing Systems: Evaluate if EN 10216-2 materials are acceptable replacements
Documentation: When DIN 1629 is unavoidable, insist on full testing and certification
Fabrication: Follow modern welding procedures even with legacy materials
Inspection: Apply current NDE standards to ensure integrity
*Note: For pressure equipment subject to the European Pressure Equipment Directive (PED), materials must be from harmonized standards – DIN 1629 is not a harmonized standard, making EN 10216-2 mandatory for CE marking.*
