Grade ST45 Seamless Carbon Steel Pipe
Overview
ST45 is a historical German material grade designation for higher-strength carbon steel pipes and tubes. It refers to material with minimum tensile strength of approximately 45 kg/mm² (≈ 441 MPa). Like ST35, this designation is obsolete and has been superseded by modern European (EN) standards, but may appear in legacy German systems.
Important: ST45 is NOT a current standard. It was part of the old DIN 1629 and DIN 17175 standards, replaced by EN 10216 series. ST45 represents a higher strength alternative to ST35.
Historical Grades & Modern Equivalents
| Old DIN Designation | Equivalent EN 10216-2 Grade | Key Characteristics |
|---|---|---|
| ST45.0 | P265TR2 | Higher strength carbon steel, room temperature |
| ST45.4 | P265GH | Higher strength for elevated temperatures (to 350°C) |
| ST45.8 | P265GH (or higher) | Higher strength for high temperature service |
Nomenclature Decoded:
ST = Steel ("Stahl")
45 = Approximate tensile strength in kg/mm²
.0/.4/.8 = Quality/application level
Higher number = Higher strength than ST35 grades
Typical Properties (Historical Reference)
| Property | ST45.0 | ST45.4 | ST45.8 |
|---|---|---|---|
| Tensile Strength | 410-530 MPa | 410-570 MPa | 410-570 MPa |
| Yield Strength | ≥ 255 MPa | ≥ 265 MPa | ≥ 265 MPa |
| Elongation | ≥ 21% | ≥ 22% | ≥ 22% |
| Max Temperature | 300°C | 300°C | 350°C |
*ST45.8 had slightly better elevated temperature properties than ST45.0/4*
Chemical Composition (Historical, Maximum %)
| Element | ST45.0/4 | ST45.8 |
|---|---|---|
| Carbon (C) | 0.21 | 0.21 |
| Silicon (Si) | 0.35 | 0.35 |
| Manganese (Mn) | 1.20 | 1.20 |
| Phosphorus (P) | 0.035 | 0.035 |
| Sulfur (S) | 0.035 | 0.035 |
| Aluminum (Altot) | ≥ 0.020 | ≥ 0.020 |
Key Differences from ST35:
Higher Carbon: 0.21% vs 0.17% (ST35)
Higher Manganese: Up to 1.20% vs 0.80% (ST35)
Results in higher strength but slightly reduced weldability
Modern Replacement: EN 10216-2 P265GH
Why P265GH Replaces ST45:
| Aspect | ST45 (Obsolete) | P265GH (Current) |
|---|---|---|
| Standard Status | Withdrawn DIN standard | Current EN harmonized standard |
| Yield Strength | ≥ 255-265 MPa | ≥ 265 MPa |
| Tensile Strength | 410-570 MPa | 410-570 MPa |
| Temperature Rating | Up to 350°C | Up to 350°C (guaranteed) |
| Chemical Control | Basic controls | Stricter (S ≤ 0.020%, P ≤ 0.025%) |
| Traceability | Limited | Full EN 10204 3.2 certification |
| Application | Obsolete | Modern high-temperature service |
P265GH Key Specifications:
Minimum Yield: 265 MPa
Tensile Range: 410-570 MPa
Carbon Max: 0.20% (vs 0.21% for ST45)
Manganese Max: 1.40% (vs 1.20% for ST45)
Sulfur Max: 0.020% (vs 0.035% for ST45)
Aluminum: ≥ 0.020% (fine grain killed)
Heat Treatment: Normalized or normalized & tempered
Comparison: ST35 vs ST45
| Parameter | ST35.8 | ST45.8 | Difference |
|---|---|---|---|
| Tensile Strength | 360-510 MPa | 410-570 MPa | +50-60 MPa higher |
| Yield Strength | ≥ 235 MPa | ≥ 265 MPa | +30 MPa higher |
| Carbon Content | 0.17% max | 0.21% max | Higher for strength |
| Manganese | 0.80% max | 1.20% max | Higher for strength |
| Weldability | Better | Slightly reduced | Higher CE value |
| Typical Use | General pressure | Higher pressure/temp | More demanding service |
Manufacturing Process (Historical)
Production for Seamless ST45:
Steel Making: Similar to ST35 but with adjusted chemistry
Deoxidation: Aluminum killed for fine grain structure
Hot Working: Mannesmann plug mill process
Heat Treatment:
ST45.0/ST45.4: Often as-rolled or normalized
ST45.8: Normalized or normalized & tempered
Testing: Mechanical and hydrostatic tests
Size Range (Typical):
Outside Diameter: 21.3 mm to 406.4 mm
Wall Thickness: 2.0 mm to 40.0 mm
Length: 6-12 meters
Applications (Historical & Modern)
Traditional Uses of ST45:
Higher Pressure Systems: Where ST35 strength was insufficient
Power Generation: Intermediate temperature steam lines
Industrial Boilers: Higher pressure sections
Chemical Plants: Process lines requiring higher strength
German Engineering: Where design required higher strength than ST35
Modern Applications of P265GH:
Boiler Tubes: For higher pressure/temperature sections
Heat Exchangers: Where higher strength needed
Process Piping: Higher pressure steam, process fluids
Power Plants: Main steam lines at moderate pressure
Industrial: Applications requiring 265 MPa yield strength
Ordering Modern Equivalent
For New Projects/Replacements:
Specify: EN 10216-2 P265GH Seamless Pipe
Sample Order Specification:
text
Material: Seamless steel tube to EN 10216-2 Grade: P265GH Heat treatment: Normalized (+N) or Normalized & Tempered (+NT) Dimensions: [OD in mm] × [wall thickness in mm] × [length in mm] Quantity: [number of pieces or meters] End preparation: [plain, bevelled, etc.] Certification: EN 10204 3.2 with full traceability Additional requirements: [if any special testing needed] Marking: Per EN 10216-2 including heat number
When to Choose P265GH vs P235GH:
| Criteria | Choose P235GH | Choose P265GH |
|---|---|---|
| Design Pressure | ≤ 100 bar | > 100 bar |
| Wall Thickness | Standard | Want to reduce wall thickness |
| Existing System | Replacing ST35 | Replacing ST45 |
| Design Standard | Calls for 235 MPa yield | Calls for 265 MPa yield |
| Cost Sensitivity | More cost-sensitive | Can afford slight premium |
Testing & Inspection
For Modern P265GH:
Hydrostatic Test: Mandatory, calculated pressure
Tensile Test: Room temperature, transverse specimens
Impact Test: Optional (not mandatory for P265GH)
Hardness Test: Optional, often specified
NDE: Ultrasonic testing optional for critical applications
Special Considerations:
Higher strength means higher test pressures
Carbon equivalent higher than P235GH (affects weldability)
May require more stringent welding procedures
Fabrication & Welding
Welding P265GH (vs P235GH):
| Aspect | P235GH | P265GH |
|---|---|---|
| Carbon Equivalent | Lower (~0.35) | Higher (~0.40) |
| Preheat | Generally not needed for thin walls | May be needed for thicker sections |
| Filler Metal | ER70S-6 typical | ER70S-6 or higher strength |
| Heat Input | Standard control | More critical control |
| PWHT | Optional | More likely to be specified |
Recommended Practice:
Calculate CE: CE=C+Mn6CE=C+6Mn ≈ 0.40 for P265GH
Preheat: For wall thickness > 25 mm or ambient temperature < 5°C
Procedure Qualification: Recommended for critical applications
PWHT: Consider for thick sections or restrained joints
Design Considerations
Advantages of P265GH over P235GH:
Higher Allowable Stress: At both room and elevated temperatures
Thinner Walls Possible: For same pressure rating
Weight Savings: Reduced material weight
Space Savings: Smaller pipe bundles possible
Disadvantages:
Higher Cost: 5-15% premium over P235GH
Reduced Weldability: Higher carbon equivalent
Less Ductility: Slightly lower elongation
More Critical Fabrication: Requires more care
Economic Analysis:
text
Example: 12" Schedule 40 Pipe - P235GH: Wall = 10.31 mm, Weight = 72.4 kg/m - P265GH: Wall = 9.53 mm (for same pressure), Weight = 66.9 kg/m - Savings: 7.6% weight reduction - Cost: P265GH costs ~8% more per kg - Net: Slight cost saving with P265GH
Industry Migration Path
From ST45 to Modern Standards:
text
ST45.0/ST45.4 → P265GH (EN 10216-2) ↓ For higher temperatures: 16Mo3 (500°C max) ↓ For higher strength: P295GH (295 MPa yield)
Alternative Paths:
For non-temperature applications: EN 10216-1 P265TR2
For US projects: ASTM A106 Grade C
For general pressure: EN 10217-1 P265
Quality Assurance
Issues with Obsolete ST45:
Verification Difficult: No active standard to reference
Property Variations: Different interpretations existed
Documentation Gaps: Old certificates often incomplete
Inspection Rejection: Modern inspectors may refuse
Benefits of P265GH:
Clear Specification: Well-defined in EN 10216-2
Standard Production: Mills produce regularly
Full Testing: Comprehensive test requirements
Global Acceptance: Recognized worldwide
Cost Comparison
Price Relationships:
P265GH (standard): 100% (baseline)
P235GH: 90-95%
"ST45" (if available): 120-150%
16Mo3 (alloy): 130-160%
ASTM A106 Gr. C: 95-105%
Total Cost Considerations:
Material Cost: P265GH premium over P235GH
Fabrication Cost: Slightly higher for P265GH
Weight Savings: May offset material premium
Lifecycle Cost: Similar for both grades
Availability: P265GH readily available vs special order for "ST45"
Regulatory Compliance
ST45 Issues:
Not PED Compliant: Cannot be CE marked
Withdrawn Standard: No longer recognized
Project Rejection: May cause project delays/rejections
Liability Concerns: Using obsolete materials increases risk
P265GH Compliance:
PED Compliant: Can be CE marked
Harmonized Standard: Listed in Official Journal
Project Acceptance: Widely accepted
Reduced Risk: Modern, documented material
Procurement Strategy
When Encountering "ST45":
Identify Exact Grade: ST45.0, .4, or .8?
Check Application: Temperature, pressure, service
Consult Engineer: Get approval for P265GH substitution
Update Documentation: Revise specs/drawings
Procure P265GH: From approved supplier
Supplier Questions to Ask:
Can you supply EN 10216-2 P265GH?
Do you have EN 10204 3.2 certification?
What heat treatment do you provide?
Can you supply required testing?
What is lead time and cost?
Technical Summary
ST45 was a higher-strength carbon steel pipe grade in the old German system, providing approximately 265 MPa minimum yield strength vs 235 MPa for ST35. It has been completely replaced by EN 10216-2 P265GH.
Key Technical Points:
Strength Level: 265 MPa minimum yield (30 MPa higher than P235GH)
Temperature Range: Up to 350°C (same as P235GH)
Chemistry: Higher carbon/manganese than P235GH for strength
Weldability: Slightly reduced due to higher carbon equivalent
Applications: Higher pressure/temperature than P235GH applications
Selection Guidelines:
Choose P265GH when:
Replacing ST45 in existing systems
Design requires ≥265 MPa yield strength
Want to reduce wall thickness vs P235GH
Higher pressure applications (typically >100 bar)
Moderate cost premium acceptable
Choose P235GH when:
Replacing ST35 in existing systems
Design requires only 235 MPa yield strength
Maximum weldability needed
Cost minimization important
Standard pressure applications
Modern Equivalent Options:
Primary: EN 10216-2 P265GH (direct replacement)
Alternative: EN 10216-1 P265TR2 (for ≤300°C only)
US Standard: ASTM A106 Grade C
Higher Temp: 16Mo3 for temperatures to 500°C
Final Recommendation:
Never specify "ST45" for new projects. Always use EN 10216-2 P265GH for seamless pipe requiring 265 MPa yield strength with guaranteed elevated temperature properties. The modern standard provides superior quality assurance, regulatory compliance, and global acceptance while maintaining the technical performance originally provided by ST45.
For maintenance of existing ST45 systems, P265GH is generally an acceptable replacement, but engineering review should confirm suitability for the specific application, particularly regarding welding and fabrication requirements which may differ slightly due to chemistry variations.
