Introduction
One of the most common questions in steel tubing selection is whether to use seamless or welded product. Both have their place, and understanding the differences helps you make the right choice for your application.
ASTM A519 is the primary specification governing seamless carbon and alloy steel mechanical tubing in North America, and understanding this standard is essential for anyone sourcing precision tubing for machining, hydraulic, or structural applications.
Manufacturing Processes
Seamless Tubing
How It's Made:
- Start with a solid round billet
- Heat the billet to forging temperature
- Pierce the center using a rotary piercing mill
- Elongate and size using pilger mills or draw benches
- Heat treat and finish as required
- No weld seam (homogeneous structure)
- Uniform properties around circumference
- Can be produced in heavier walls
- Higher production cost
Welded Tubing (ERW)
How It's Made:
- Start with flat-rolled steel (strip or coil)
- Form into tubular shape
- Weld the longitudinal seam using electric resistance welding (ERW)
- Size and straighten
- Heat treat weld zone or full body as required
- Contains a longitudinal weld seam
- Excellent dimensional consistency
- Lower production cost
- Limited to thinner walls relative to diameter
Property Comparison
Mechanical Properties
| Property | Seamless | Welded (ERW) |
|---|
| Tensile Strength | Uniform | May vary at weld | ||||
| Yield Strength | Uniform | Typically uniform | ||||
| Elongation | Good | Good | ||||
| Impact Toughness | Excellent | Good (depends on weld quality) | ||||
| Fatigue Life | Superior | Good | Dimensional Characteristics | Characteristic | Seamless | Welded |
|---|
| Wall Tolerance | Wider | Tighter |
| OD Tolerance | Standard | Excellent |
| Concentricity | Variable | Excellent |
| Straightness | Good | Excellent |
| Surface Finish | Standard | Can be very smooth |
When to Choose Seamless
Required Applications
- High-pressure services exceeding certain limits
- Critical fatigue applications
- Sour service (H2S environments)
- Many ASME code applications
- API OCTG specifications
Preferred Applications
- Thick wall requirements
- Elevated temperature service
- Rotating or dynamic loads
- Maximum reliability required
- Small diameter, heavy wall
When to Choose Welded
Cost-Effective Applications
- Structural applications
- Lower pressure services
- Static loading conditions
- Large quantities of standard sizes
- Tight dimensional tolerances required
Ideal Applications
- Hydraulic cylinder tubing (DOM)
- Mechanical tubing for precision parts
- Automotive components
- Furniture and architectural uses
- Heat exchanger tubing
Special Product: DOM Tubing
Drawn Over Mandrel (DOM) tubing starts as welded tubing but undergoes additional processing:
- ERW welded tube is produced
- Cold drawn over a mandrel
- Results in refined weld zone and improved properties
- Seamless-like properties at welded tubing cost
- Excellent surface finish
- Tight tolerances
- Good for hydraulic applications
Specification Guidance
ASTM A519 - The Gold Standard for Seamless Mechanical Tubing
ASTM A519 covers seamless carbon and alloy steel mechanical tubing for applications including:
- Hydraulic cylinders and systems
- Automotive components (axles, drive shafts, steering columns)
- Machine parts requiring precision boring or machining
- Structural applications where weld seams are unacceptable
- Any application requiring superior concentricity and surface finish
- Available in grades 1010, 1020, 1026, 4130, 4140, 4145H, and many more
- Multiple conditions: Hot Finished (HF), Cold Drawn (CD), Stress Relieved (SR), Annealed (A), Normalized (N), Quenched & Tempered (Q&T)
- OD range from 0.500" to over 10.750"
- Wall thickness from 0.035" to 1.500"+ depending on OD
- Full traceability with MTRs to ASTM requirements
Other Seamless Specifications
- ASTM A106: Pressure piping (higher temperature service)
- API 5CT: OCTG casing and tubing
- API 5L: Line pipe (PSL2 often seamless)
Welded Specifications
- ASTM A513: ERW mechanical tubing
- ASTM A513 Type 5: DOM tubing (cold drawn over mandrel)
- ASTM A53 Type E: ERW pressure pipe
- API 5L: Line pipe (many grades available ERW)
Cost Considerations
General pricing relationship (same size and grade):
- ERW Welded: Baseline
- DOM: 10-20% premium over ERW
- Seamless: 30-100%+ premium over ERW
- Size and wall thickness
- Grade and specification
- Quantity and availability
Making Your Selection
Questions to Ask:
- What are the pressure/stress requirements?
- Is the application covered by a code requiring seamless?
- What are the fatigue and dynamic loading conditions?
- What dimensional tolerances are needed?
- What is the budget constraint?
OSS Metals Inventory
We stock both seamless and welded tubing products:
- Seamless mechanical tubing (ASTM A519)
- DOM tubing (ASTM A513 Type 5)
- OCTG products (API 5CT)
- Custom sizes and grades available
Related Topics
seamless tubingwelded tubingsteel pipeASTM A519ERW pipe