13CrMo44 Seamless Chrome-Molybdenum Steel Pipe
Overview
13CrMo44 is a chromium-molybdenum alloy steel grade for seamless tubes used in high-temperature and high-pressure service. It is part of the modern European EN 10216-2 standard, representing a specific 1% chromium, 0.5% molybdenum alloy steel with guaranteed elevated temperature properties. This grade is widely used in power generation, petrochemical, and refinery applications.
Important Note: 13CrMo44 is a current, active standard (not obsolete like ST grades). The "44" suffix indicates specific property requirements, not an obsolete designation.
Standard & Specification
| Standard | Designation | Status | Key Application |
|---|---|---|---|
| EN 10216-2 | 13CrMo4-5 | Current | Seamless tubes for pressure purposes at elevated temperatures |
| DIN 17175 | 13CrMo44 | Historical | Previous German designation (largely equivalent) |
| ISO 9329-2 | 13CrMo4-5 | International | ISO adoption of EN standard |
Nomenclature Explained:
13 = Approximately 1% Chromium (actual range 0.70-1.15%)
CrMo = Chromium-Molybdenum alloy steel
44 = Historical designation for specific property level
4-5 = Modern EN designation indicating Cr-Mo alloy with specific properties
Mechanical Properties
Room Temperature Requirements:
| Property | Minimum Requirement | Typical Range |
|---|---|---|
| Yield Strength (Rp0.2) | ≥ 280 MPa | 280-350 MPa |
| Tensile Strength (Rm) | 440-590 MPa | 480-550 MPa (typical) |
| Elongation (A) | ≥ 22% | 22-28% |
| Reduction of Area (Z) | Not specified | Typically ≥ 50% |
Elevated Temperature Properties (Guaranteed):
| Temperature | 0.2% Proof Stress Min | Tensile Strength Min |
|---|---|---|
| 250°C | 225 MPa | - |
| 300°C | 215 MPa | - |
| 350°C | 205 MPa | - |
| 400°C | 195 MPa | - |
| 450°C | 185 MPa | - |
| 500°C | 175 MPa | - |
| 550°C | 140 MPa | - |
Properties decrease gradually with temperature - characteristic of Cr-Mo steels
Chemical Composition (Maximum %)
| Element | Minimum | Maximum | Purpose/Effect |
|---|---|---|---|
| Carbon (C) | - | 0.15 | Strength, limited for weldability |
| Silicon (Si) | - | 0.35 | Deoxidizer, strength |
| Manganese (Mn) | 0.40 | 1.00 | Strength, hardenability |
| Phosphorus (P) | - | 0.025 | Impurity control |
| Sulfur (S) | - | 0.020 | Impurity control (low for weldability) |
| Chromium (Cr) | 0.70 | 1.15 | Creep resistance, oxidation resistance |
| Molybdenum (Mo) | 0.45 | 0.65 | Creep strength, tempering resistance |
| Aluminum (Altot) | 0.020 | - | Grain refinement (fine grain steel) |
Key Features:
Low Carbon: ≤0.15% for good weldability
Controlled Cr-Mo: Precise ranges for optimal creep properties
Fine Grain: Aluminum killed for consistent properties
Clean Steel: Low sulfur and phosphorus
Manufacturing Process
Production of Seamless 13CrMo44:
Steel Making: Electric arc or basic oxygen furnace
Secondary Refining: Ladle furnace treatment for precise chemistry
Continuous Casting: Fine grain practice
Hot Working: Mannesmann process or extrusion
Heat Treatment: Mandatory - Normalized & Tempered
Finishing: Straightening, cutting, testing
Mandatory Heat Treatment:
Normalizing: 900-960°C, air cooling
Tempering: 680-750°C, minimum 30 minutes per 25mm thickness
Result: Tempered bainitic/martensitic structure for optimal creep resistance
Size Range:
Outside Diameter: 21.3 mm to 711 mm (≈ ½" to 28")
Wall Thickness: 2.0 mm to 80.0 mm
Length: Typically 6-12m; up to 18m available
Testing & Inspection Requirements
Mandatory Tests (EN 10216-2):
| Test | Standard | Frequency | Acceptance Criteria |
|---|---|---|---|
| Hydrostatic Test | EN 10216-2 Clause 8 | 100% | Pressure = 20×S×t/D (bar), ≥10 sec |
| Tensile Test | EN ISO 6892-1 | Per heat, per wall | Room temp + elevated temp optional |
| Impact Test | EN ISO 148-1 | Mandatory | 40J minimum at 20°C (typical) |
| Hardness Test | EN ISO 6506-1 | Often required | Typically 140-180 HB |
| Flattening Test | EN ISO 8492 | For D≤50mm, t/D≤0.1 | No cracking to specified distance |
| Ultrasonic Test | EN 10246-3 | Optional/agreed | For laminations, inclusions |
Special Requirements for 13CrMo44:
Impact Testing Mandatory: Unlike some carbon steel grades
Hardness Control: Critical for creep and weldability
Microstructure Check: Often specified for verification
NDE: More commonly specified than for carbon steels
Heat Treatment Specifications
Standard Condition:
Delivery: Normalized & Tempered (+NT)
Normalizing: 900-960°C, air cool
Tempering: 680-750°C, hold time appropriate for wall thickness
Cooling: Air cool after tempering
Microstructure After Heat Treatment:
Primary: Tempered bainite
Grain Size: ASTM 5 or finer
Carbide Distribution: Fine, uniform dispersion
No untempered martensite allowed
Hardness After Heat Treatment:
Typical: 140-180 HB
Maximum: Usually specified ≤200 HB for weldability
Uniformity: Through wall thickness and along length
Applications
Primary Industries:
Power Generation: Superheater tubes, reheater tubes, high-pressure steam lines
Petrochemical: Reformer tubes, heater tubes, high-temperature process piping
Refining: Hydrocracker, catalytic cracker, visbreaker units
Chemical Industry: High-temperature reactors, heat exchangers
Industrial Boilers: High-pressure sections
Typical Service Conditions:
Temperature Range: 400-550°C (optimal range)
Pressure: High pressure (100-200 bar typical)
Media: Superheated steam, hot process gases, thermal oils
Environment: High-temperature oxidation conditions
Why 13CrMo44 is Selected:
Creep Resistance: Superior to carbon steels at 450-550°C
Oxidation Resistance: Chromium provides scaling resistance
Microstructural Stability: Maintains properties at temperature
Good Weldability: For a low-alloy creep-resistant steel
Cost-Effective: Less expensive than higher alloy steels
Comparison with Similar Grades
| Grade | Cr Content | Mo Content | Max Temp | Key Difference |
|---|---|---|---|---|
| 16Mo3 | - | 0.25-0.35% | 500°C | Mo steel only, lower temp |
| 13CrMo44 | 0.70-1.15% | 0.45-0.65% | 550°C | Cr+Mo, better creep |
| 10CrMo9-10 | 2.00-2.50% | 0.90-1.20% | 580°C | Higher Cr, better oxidation |
| P235GH | - | - | 350°C | Carbon steel, lower temp |
Advantages over Carbon Steels:
50-100°C higher temperature capability
Better creep rupture strength
Improved oxidation resistance
Better microstructural stability
Advantages over Higher Alloys:
Better weldability than higher Cr-Mo steels
Lower cost than 9% Cr or austenitic steels
Lower thermal expansion than austenitics
Familiar fabrication for most shops
Fabrication & Welding
Welding 13CrMo44 (Critical Considerations):
| Parameter | Requirement | Reason |
|---|---|---|
| Preheat | 150-250°C | Prevent hydrogen cracking |
| Interpass Temp | 250-350°C max | Control microstructure |
| Filler Metal | 2.25Cr-1Mo or matching | Typically ER90S-B3, E8018-B2 |
| PWHT | Mandatory | 680-750°C, similar to base metal |
| Heat Input | Controlled (1-2 kJ/mm) | Prevent HAZ degradation |
| Procedure Qual | Mandatory + testing | Often includes creep tests |
Carbon Equivalent:
Pcm=C+Si30+Mn+Cu+Cr20+Ni60+Mo15+V10+5BPcm=C+30Si+20Mn+Cu+Cr+60Ni+15Mo+10V+5B
Typical: 0.25-0.30 (better than higher alloy steels)
Common Welding Issues:
HAZ Softening: If PWHT temperature too high
Reheat Cracking: In HAZ during PWHT
Hydrogen Cracking: If preheat insufficient
Creep Mismatch: If filler metal not properly selected
Recommended Practice:
Qualify procedures per EN ISO 15614-1
Use low-hydrogen processes (TIG, SMAW with baked electrodes)
Control interpass temperature carefully
PWHT within 24 hours of welding completion
Consider post-weld NDE (UT, RT)
Design Considerations
Allowable Stresses (Example):
| Temperature | Allowable Stress (MPa) | Comparison to P235GH |
|---|---|---|
| 20°C | 147 | Similar |
| 300°C | 125 | Higher |
| 400°C | 115 | Significantly higher |
| 500°C | 75 | Much higher |
| 550°C | 45 | Carbon steel not rated |
Design Advantages:
Higher allowable stresses at elevated temperatures
Thinner walls possible for same pressure/temperature
Longer service life at high temperatures
Better corrosion/oxidation resistance
Limitations:
Maximum temperature: ~550°C (for long-term service)
Not for severe corrosion: Limited chromium content
Welding complexity: More than carbon steels
Cost: 2-3× carbon steel price
Material Certification & Traceability
Required Documentation (EN 10204 3.2):
Chemical Analysis: Full spectrochemical report
Mechanical Tests: Tensile (room + optional elevated), impact
Hardness Test: Typically Brinell or Vickers
Heat Treatment Records: Times, temperatures, cooling rates
NDE Reports: If ultrasonic or other NDE performed
Traceability: Complete from melt to finished tube
Marking Requirements:
Manufacturer's identification
EN 10216-2 designation
Grade: 13CrMo4-5
Size: D × t
Heat number
Heat treatment symbol (+NT)
CE marking (for PED applications)
Inspector's mark
Ordering Information
Complete Specification Example:
text
Seamless tubes to EN 10216-2 Grade: 13CrMo4-5 Heat treatment: Normalized & Tempered (+NT) Dimensions: 114.3 mm OD × 8.0 mm WT × 8000 mm length Quantity: 80 pieces End preparation: Bevelled 37.5° ± 2.5°, 1.6mm land Certification: EN 10204 3.2 certificate in English Testing: - Tensile test at room temperature - Charpy impact test: 3 specimens at 20°C (min 40J avg, 32J single) - Hardness test: HB report - Optional: Elevated temperature tensile at 500°C NDE: Full-length ultrasonic testing Marking: Per EN 10216-2, include heat number and "UT"
Key Points to Specify:
Standard & Grade: EN 10216-2 13CrMo4-5
Heat Treatment: +NT (Normalized & Tempered)
Impact Test Temperature: Usually 20°C, but can specify other
Hardness Limits: If specific maximum required
NDE Requirements: UT often specified for critical service
End Preparation: For welding or other connections
Industry Usage & Standards Cross-Reference
European Power Industry:
Standard material for superheater tubes in conventional power plants
Widely used in European-designed boilers
Qualified by major boiler manufacturers
Global Equivalents:
| Region | Standard | Equivalent Grade | Notes |
|---|---|---|---|
| USA | ASTM A335 | P12 | Slightly different chemistry |
| Japan | JIS G3455 | STPA 23 | Similar 1Cr-0.5Mo |
| Germany | DIN 17175 | 13CrMo44 | Historical equivalent |
| International | ISO 9329-2 | 13CrMo4-5 | ISO adoption |
ASTM A335 P12 Comparison:
| Parameter | 13CrMo44 | A335 P12 |
|---|---|---|
| Cr Range | 0.70-1.15% | 0.80-1.25% |
| Mo Range | 0.45-0.65% | 0.44-0.65% |
| C Max | 0.15% | 0.15% |
| Mn Max | 1.00% | 0.60% |
| Impact Test | Mandatory | Optional |
| Application | Similar | Similar |
Quality Assurance Focus Areas
Critical Quality Parameters:
Heat Treatment: Proper normalizing and tempering
Hardness: Within specified range (typically 140-180 HB)
Impact Toughness: Minimum 40J at 20°C
Microstructure: Tempered bainite, no untempered martensite
Surface Quality: Free of decarburization, seams, laps
Common Quality Issues:
Over-tempering: Results in excessive softening
Under-tempering: Leaves untempered martensite
Decarburization: Surface carbon loss during heat treatment
Band Microstructure: From improper hot working
Excessive hardness: From improper cooling
Inspection Methods:
Ultrasonic Testing: For internal defects
Magnetic Particle: For surface defects
Metallography: For microstructure verification
Hardness Survey: Through wall thickness
Positive Material ID: For chemistry verification
Economic Considerations
Cost Factors:
| Factor | Impact on Cost | Notes |
|---|---|---|
| Material Premium | 2-3× carbon steel | Alloying elements |
| Heat Treatment | Additional 10-20% | Normalizing & tempering |
| Testing | Additional 5-15% | Impact, hardness, NDE |
| Size | Standard sizes cheapest | Custom sizes premium |
| Quantity | Volume discounts | Typically >5 tons |
Total Cost of Ownership:
Initial Cost: Higher than carbon steel
Fabrication Cost: Higher (welding, PWHT)
Installation Cost: Similar to other alloy steels
Maintenance Cost: Lower (longer life, less oxidation)
Lifecycle Cost: Often lower for high-temperature service
When 13CrMo44 is Economically Justified:
Service temperature >400°C
Design life >20 years
High-pressure service (>100 bar)
Where reliability is critical
When carbon steel would require much thicker walls
Technical Summary
13CrMo44 (EN 10216-2 13CrMo4-5) is a 1% chromium, 0.5% molybdenum low-alloy steel specifically designed for high-temperature pressure applications in the 400-550°C range. It represents an optimal balance between performance, fabricability, and cost for many industrial applications.
Key Technical Characteristics:
Temperature Capability: Optimal 400-550°C, maximum ~580°C short-term
Creep Resistance: Superior to carbon steels at elevated temperatures
Oxidation Resistance: Chromium provides protection against scaling
Weldability: Good for a creep-resistant alloy steel
Microstructure: Tempered bainite after proper heat treatment
Selection Guidelines:
Choose 13CrMo44 when:
Service temperature is 400-550°C
Creep resistance is required for long-term service
Oxidation resistance is needed but not extreme
Good weldability is important
Cost constraints preclude higher alloy steels
Replacing existing 13CrMo44 in legacy systems
Consider alternatives when:
Temperature <400°C (carbon steel may suffice)
Temperature >550°C (consider higher Cr-Mo or austenitic steels)
Severe corrosion environment (need stainless or higher alloy)
Fabrication capabilities limited for alloy steels
Cost is primary driver and temperature allows carbon steel
Implementation Best Practices:
Material Procurement:
Specify EN 10216-2 13CrMo4-5 (not obsolete designations)
Require EN 10204 3.2 certification
Specify heat treatment (+NT) and testing requirements
Consider NDE based on application criticality
Fabrication Planning:
Develop and qualify welding procedures before fabrication
Ensure fabricator has experience with Cr-Mo steels
Plan for PWHT requirements
Budget for additional testing and inspection
Quality Assurance:
Verify heat treatment records
Check impact test results meet requirements
Monitor hardness for consistency
Implement proper NDE for welds
Industry Perspective:
13CrMo44 remains a workhorse material in power generation and petrochemical industries for high-temperature piping and tubing. Its predictable behavior, established fabrication procedures, and proven service history make it a reliable choice for applications where carbon steel is inadequate but higher alloys are unnecessary.
For new projects, EN 10216-2 13CrMo4-5 should always be specified rather than historical designations. The modern standard ensures consistent quality, proper testing, and regulatory compliance for pressure equipment applications throughout Europe and increasingly worldwide.
