Understanding the Manufacturing Processes
Electric Resistance Welding (ERW)
Process: Steel coil is cold-formed and welded using high-frequency electrical resistance
No filler metal added during welding
Typical for smaller diameters (up to 24" OD)
Common standards: ASTM A53 Type E, ASTM A135
Electric Fusion Welding (EFW) - ASTM A671
Process: Pressure vessel quality plates are formed and welded using electric arc with added filler metal
Welding is typically performed as Submerged Arc Welding (SAW)
Suitable for larger diameters (16" to 100"+)
Filler metal is added during the welding process
Key Specifications for ASTM A671 EFW Pipe
| Attribute | Description |
|---|---|
| Standard | ASTM A671/A671M: Electric-Fusion-Welded Steel Pipe for Atmospheric and Lower Temperatures |
| Manufacturing Process | Electric Fusion Welded (EFW) - Submerged Arc Welding (SAW) with filler metal |
| Size Range | 16" to 100" OD (406 mm to 2540 mm) |
| Wall Thickness | 6 mm to 100 mm |
| Grades | CA55, CB60, CB65, CB70, CC60, CC65, CC70, CD80, CD90 |
| Application | High-pressure service at atmospheric and lower temperatures |
| Material Source | Pressure vessel quality plates (ASTM A516, A515, A285, etc.) |
| Longitudinal Joint Factor (E) | 1.00 (per 49 CFR 192.113 for EFW pipe) |
ASTM A671 Grades & Corresponding Plate Materials
| Pipe Grade | Corresponding Plate Specification | Plate Grade |
|---|---|---|
| CA55 | ASTM A285 | Grade A or B |
| CB60 | ASTM A515 | Grade 60 |
| CB65 | ASTM A515 | Grade 65 |
| CB70 | ASTM A515 | Grade 70 |
| CC60 | ASTM A516 | Grade 60 |
| CC65 | ASTM A516 | Grade 65 |
| CC70 | ASTM A516 | Grade 70 |
*Note: "C" grades (CC60, CC65, CC70) are typically used for low-temperature service .*
Design Factor: Longitudinal Joint Efficiency (E)
Under both ASME B31.3 and 49 CFR 192, the longitudinal joint factor (E) is a critical design parameter that affects required wall thickness:
| Pipe Type | E Factor (per ASME B31.3) | E Factor (per 49 CFR 192) |
|---|---|---|
| Seamless | 1.00 | 1.00 |
| ERW (Type E) | 0.85 | 1.00 |
| EFW (ASTM A671) | 0.85 (spot RT) to 1.00 (100% RT) | 1.00 |
Important: For ERW pipe, many design codes apply a joint efficiency factor of 0.85, meaning ERW pipe requires approximately 18% thicker walls than seamless for the same pressure . ASTM A671 EFW pipe can achieve E=1.00 with full radiographic examination .
Applications
ASTM A671 EFW pipe is used for :
Power plant piping systems
Chemical and petrochemical processing
Offshore oil and gas platforms
Refinery piping at moderate temperatures
Low-temperature service applications
Large-diameter fluid transmission
Why This Distinction Matters
| Aspect | ERW Pipe (e.g., ASTM A53) | ASTM A671 (EFW) |
|---|---|---|
| Manufacturing | Coil → Cold-formed → Welded | Plate → Formed → Welded with filler |
| Typical Diameter | Up to 24" | 16" to 100"+ |
| Wall Thickness | Limited | Up to 100 mm |
| Material Source | Steel coil | Pressure vessel quality plate |
| Weld Type | Resistance weld | Fusion weld with filler |
| Application Focus | General service, low pressure | High-pressure, low temperature |
| Certification | Mill certificate | EN 10204 3.1 or 3.2 |
Summary
ASTM A671 is an EFW (Electric-Fusion-Welded) specification, not ERW. If you require ERW pipe, specify ASTM A53 Type E or ASTM A135. If your application requires large diameters, thick walls, or high-pressure service at low temperatures, ASTM A671 EFW is the appropriate specification .
When ordering ASTM A671 pipe, specify:
Grade (e.g., CC70 for low-temperature service)
Class (e.g., Class 22 for stress-relieved with full RT and hydrotest)
Dimensions (OD, wall thickness, length)
End Finish (plain or beveled)
Certification (EN 10204 Type 3.1 or 3.2)
