ASTM A672 Electric-Fusion-Welded (EFW) Pipe
Basic Overview
ASTM A672 is the standard specification for electric-fusion-welded (EFW) steel pipe fabricated from pressure vessel quality plates, designed for high-pressure service at moderate temperatures [citation:2, citation:4]. Unlike ERW pipe (which uses no filler metal), A672 pipes are welded with added filler metal, typically using the Submerged Arc Welding (SAW) process, resulting in a strong, reliable longitudinal seam suitable for demanding applications [citation:3, citation:5].
Key Features
| Feature | Description |
|---|---|
| Manufacturing Process | Electric-Fusion Welded (EFW) with filler metal added; typically Longitudinal Submerged Arc Welded (LSAW) or Double Submerged Arc Welded (DSAW) [citation:2, citation:5] |
| Material Source | Pressure vessel quality plates (ASTM A285, A515, A516, A537, etc.) [citation:3, citation:5, citation:8] |
| Primary Application | High-pressure service at moderate temperatures (-29°C to 343°C / -20°F to 650°F) [citation:3, citation:5] |
| Diameter Range | 16 inches (400 mm) and larger nominally; up to 60" or more [citation:2, citation:4] |
| Wall Thickness | Up to 3 inches (75 mm) inclusive [citation:2, citation:4] |
| Length | Typically 6 m and 12 m; custom lengths available |
| Heat Treatment | Per Class requirements (stress relieved, normalized, quenched & tempered) [citation:3, citation:4] |
Grade Designation System
ASTM A672 uses a two-part designation system: Grade (indicating the plate material) and Class (indicating heat treatment and inspection level).
Grades (Plate Material)
| Grade | Corresponding Plate Specification | Steel Type |
|---|---|---|
| A45, A50, A55 | ASTM A285 Gr. A, B, C | Carbon steel (low/intermediate tensile) |
| B55, B60, B65, B70 | ASTM A515 Gr. 55, 60, 65, 70 | Carbon steel, killed, moderate temperature service [citation:3, citation:8] |
| C55, C60, C65, C70 | ASTM A516 Gr. 55, 60, 65, 70 | Carbon steel, killed, fine grain, improved toughness [citation:3, citation:8] |
| D70, D80 | ASTM A537 Cl. 1, 2 | Manganese-silicon, normalized or Q&T |
| E55, E60 | ASTM A442 Gr. 55, 60 | Carbon steel |
| H75, H80 | ASTM A302 Gr. A, B, C, D | Manganese-molybdenum |
| J80, J90, J100 | ASTM A533 Cl. 1, 2, 3 | Manganese-molybdenum, Q&T |
| K75, K85 | ASTM A202 Gr. A, B | Chromium-manganese-silicon |
| L65, L70, L75 | ASTM A204 Gr. A, B, C | Molybdenum |
| N75 | ASTM A299 | Manganese-silicon |
*Note: Grade numbers indicate approximate minimum tensile strength in ksi (e.g., B60 = 60,000 psi minimum tensile strength).*
Class Designations (Heat Treatment & Inspection)
The Class number follows a logical pattern where the first digit indicates heat treatment type and the second digit indicates inspection level [citation:3, citation:4]:
| Class | Heat Treatment | Radiography (RT) | Pressure Test | Joint Factor (E) |
|---|---|---|---|---|
| 10, 12 | None | No / Yes | No / Yes | 0.85 |
| 20, 22 | Stress Relieved | No / Yes | No / Yes | 0.90 |
| 30, 32 | Normalized | No / Yes | No / Yes | 1.00 |
| 40, 42 | Normalized & Tempered | No / Yes | No / Yes | 1.00 |
| 50, 52 | Quenched & Tempered | No / Yes | No / Yes | 1.00 |
Most Common Selections:
Class 12: As-welded, fully inspected (RT + hydrotest) – for general service
Class 22: Stress relieved, fully inspected – standard for many applications
Class 32: Normalized, fully inspected – when grain refinement is needed
Class 42: Normalized & tempered, fully inspected – for enhanced elevated-temperature properties
Chemical Composition (Typical for Common Grades)
| Grade | Carbon (C) max % | Silicon (Si) % | Manganese (Mn) max % | Phosphorus (P) max % | Sulfur (S) max % |
|---|---|---|---|---|---|
| A45/A50/A55 | 0.17-0.28 | - | 0.98 | 0.035 | 0.035 |
| B55/B60/B65/B70 | 0.20-0.31 | 0.13-0.45 | 1.30 | 0.035 | 0.035 |
| C55/C60/C65/C70 | 0.18-0.27 | 0.55-0.98 | 0.79-1.30 | 0.035 | 0.035 |
Source:
Mechanical Properties (Base Metal)
| Grade | Yield Strength (MPa) min | Tensile Strength (MPa) | Elongation % (longitudinal) | Weld Tensile Strength (MPa) min |
|---|---|---|---|---|
| A45 | 165 | 310-450 | 30 | 310-450 |
| A50 | 185 | 345-485 | 28 | 345-485 |
| A55 | 205 | 380-515 | 27 | 380-515 |
| B55 | 205 | 380-515 | 27 | 380-515 |
| B60 | 220 | 415-550 | 25 | 415-550 |
| B65 | 240 | 450-585 | 23 | 450-585 |
| B70 | 260 | 485-620 | 21 | 485-620 |
| C55 | 205 | 380-515 | 27 | 380-515 |
| C60 | 220 | 415-550 | 25 | 415-550 |
| C65 | 240 | 450-585 | 23 | 450-585 |
| C70 | 260 | 485-620 | 21 | 485-620 |
Source:
Note: Welding point tensile strength must meet or exceed the minimum tensile strength of the base metal grade.
Dimensional Tolerances
| Parameter | Tolerance |
|---|---|
| Outside Diameter (D ≤ 406.4mm) | ±0.75% or ±3mm (whichever is greater) |
| Outside Diameter (D > 406.4mm) | ±0.75% or ±5mm (whichever is greater) |
| Wall Thickness (t ≤ 15mm) | +10% / -5% |
| Wall Thickness (t > 15mm) | +8% / -3% |
| Straightness | ≤ 0.15% of total length (max 3mm per meter) |
| Length | +50mm / -0mm (fixed lengths) |
Testing & Inspection Requirements
| Test Type | Purpose | Applicability |
|---|---|---|
| Chemical Analysis | Verify composition of plate material (each mill heat) | All grades |
| Weld Metal Analysis | Verify composition of finished deposited weld material (each 500 ft) | All pipes |
| Tension Test | Verify yield and tensile strength (one per lot) | All grades |
| Transverse Guided Weld Bend Test | Verify weld ductility and integrity (two specimens per lot) | All pipes |
| Radiographic Examination (RT) | Detect weld defects – full length of each weld | Required for Classes with "1" or "2" as second digit [citation:3, citation:4] |
| Hydrostatic Test | Proof of leak-tightness | Required for Classes with "2" or "3" as second digit [citation:3, citation:4] |
| Non-Destructive Testing (NDT) | Weld seam and pipe body inspection | Per Class requirements [citation:2, citation:5] |
Comparison: ASTM A672 vs. A671 vs. A691
| Aspect | ASTM A672 | ASTM A671 | ASTM A691 |
|---|---|---|---|
| Service Temperature | Moderate temperatures (-29°C to 343°C) | Atmospheric and lower temperatures (down to -46°C) | High temperatures (up to 593°C) |
| Primary Focus | Elevated temperature strength, high-pressure capability | Low-temperature toughness, impact properties | High-temperature strength, creep resistance |
| Typical Grades | B60, B65, B70 (A515-based) | CC60, CC65, CC70 (A516-based) | 1CR, 1.25CR, 2.25CR, 5CR, 9CR (Cr-Mo alloys) |
| Material Type | Carbon steel (killed) | Carbon steel (killed/fine grain) | Chrome-moly alloy steel |
| Common Applications | Power plant steam lines, boiler external piping, geothermal | Low-temperature process piping, LNG, cold service | High-temperature steam lines, refinery heaters |
Common Applications
| Industry | Applications |
|---|---|
| Power Generation | Boiler external piping, steam lines, feedwater systems, high-pressure steam conveyance |
| Geothermal | Steam and hot water pipelines under pressure |
| Oil & Gas | Transmission lines, refinery piping, high-pressure process lines |
| Petrochemical | High-pressure process piping, chemical plant lines |
| Infrastructure | Industrial piping systems requiring moderate to high pressure |
| Water Transmission | Large-diameter high-pressure water mains |
Key Advantages
| Advantage | Description |
|---|---|
| Large Diameter Capability | Can produce pipes much larger than seamless or ERW capabilities (16" to 60"+) [citation:2, citation:4] |
| Thick Walls | Suitable for high-pressure applications requiring substantial wall thickness (up to 75 mm) [citation:2, citation:4] |
| Material Flexibility | Wide range of plate grades available for different service conditions |
| Elevated Temperature Performance | Specifically designed for moderate temperature service (up to 343°C) |
| Quality Control Options | Class system allows matching inspection level to service criticality |
| High Joint Efficiency | Class 32/42 achieves joint factor E=1.00, reducing required wall thickness |
Important Considerations
1. Grade Selection by Temperature
B-grades (A515): Preferred for moderate temperature service – specifically designed for elevated temperature applications
C-grades (A516): Fine grain, improved toughness – better for low-temperature applications
Higher number = higher strength (60, 65, 70 indicate approximate tensile strength in ksi)
2. Class Selection Logic
The class numbering system makes selection straightforward:
First digit = heat treatment: 10 (as-welded), 20 (stress relieved), 30 (normalized), 40 (normalized & tempered), 50 (quenched & tempered)
Second digit = inspection: 0 (none), 1 (RT only), 2 (RT + hydrotest), 3 (hydrotest only)
Most common selections for moderate temperature service:
Class 12: As-welded, fully inspected – for general service
Class 22: Stress relieved, fully inspected – standard for many applications
Class 32: Normalized, fully inspected – when grain refinement is needed
Class 42: Normalized and tempered, fully inspected – for enhanced elevated-temperature properties
3. Joint Efficiency Factor
For process piping designed per ASME B31.3, the joint efficiency factor (E) depends on the class :
Class 10/12: E = 0.85
Class 20/22: E = 0.90
Class 30/32/40/42/50/52: E = 1.00
Specifying Class 32 or 42 allows a joint factor of 1.0, reducing required wall thickness and pipe weight.
4. Code Compliance
ASME Code: Often adopted as SA-672 for Boiler and Pressure Vessel Code applications
Consult applicable construction codes (ASME B31.1 Power Piping, B31.3 Process Piping) for acceptance and design factors
5. Quality Assurance
Mill Test Certificate: EN 10204 Type 3.1 or 3.2 typically required for critical applications
Ensure all required testing (RT, hydrotest) per specified Class is documented
Request Mill's Inspection Report from the production batch for project design verification
Summary
ASTM A672 EFW pipe is the standard specification for large-diameter, electric-fusion-welded steel pipe fabricated from pressure vessel quality plates for high-pressure service at moderate temperatures. It is distinguished by its Grade (indicating the plate material, e.g., B70 from A515 Gr.70 for elevated temperature service) and Class (indicating heat treatment and inspection level, e.g., Class 22 for stress-relieved with radiography and hydrotest).
Available in diameters from 16 inches (400 mm) to over 60 inches with wall thicknesses up to 75 mm, A672 pipes are manufactured using double-sided submerged arc welding (DSAW) with filler metal added, ensuring high-integrity longitudinal seams. The Class system allows engineers to select the appropriate combination of heat treatment and inspection based on service criticality, with higher classes (32/42) achieving a joint efficiency factor of 1.0.
When to specify ASTM A672:
The system operates at high pressure with moderate temperatures (up to 343°C)
Carbon steel is adequate for the corrosion environment
Applications include high-pressure water, steam, and process piping in refineries, power plants, and geothermal facilities
Large diameters and thick walls are required where ERW pipe is not feasible
When ordering, specify: ASTM A672, Grade [e.g., B70], Class [e.g., 22], Size (OD x WT), Length, End Finish, and any supplementary requirements.
