ASTM A671 vs A672 EFW Carbon Steel Pipe Specification Comparison
When a project calls for large-diameter welded pipe beyond 24 inch NPS, ASTM A671 and ASTM A672 are the two specifications that dominate procurement lists. Both standards cover electric-fusion-welded (EFW) carbon steel pipe, but they target very different service conditions — atmospheric vs higher-temperature pressure service. Choosing the wrong spec leads to over-priced pipe, weld-defect rework, or premature failure in service.
This guide compares A671 and A672 head-to-head on scope, plate feedstock, weld procedure, heat treatment, mechanical-property classes, inspection regime and typical applications. Whether you are sourcing penstock, transmission line pipe, refinery service pipe or power-plant economiser pipe, the same selection rule applies: match the class letter to the lowest service temperature and the highest design pressure, then verify the plate certificate before welding.
1. Scope and Purpose of Each Standard
ASTM A671 / A671M is the specification for electric-fusion-welded steel pipe for atmospheric and lower-temperature service. The standard uses a class-letter system (CC10 through CC65) tied to the plate specification and the minimum specified tensile strength of the plate. Pipes under A671 are typically used where the design temperature does not exceed about 400°F (204°C) and the operating pressure is moderate.
ASTM A672 / A672M is the companion specification for electric-fusion-welded steel pipe for high-pressure and moderate-temperature service. A672 covers class letters from L65 to L75 for plate grades intended for service up to about 850°F (454°C). A672 pipes are required for power-station main steam, feedwater and process piping where elevated temperature and pressure coexist.
Both specifications permit EFW manufacture using either double-submerged-arc welding (DSAW) or a combination of DSAW plus gas-tungsten-arc root pass. The plate feedstock is usually produced to ASTM A516, A537, A204, A387 or A302 depending on the class, with impact-test requirements dictated by the lowest expected service temperature.
2. Class Letter System Explained
Both A671 and A672 use a two-character class designation: a letter prefix indicating plate type and weld procedure, and a two-digit number indicating the plate tensile strength in ksi. The number suffix matches the plate specification strength grade.
| A671 Class | Plate Spec | Min Tensile (ksi) | Typical Service |
|---|---|---|---|
| CC10 | A36 | 36 | Atmospheric, structural |
| CC11 | A36 / A283 | 36 | Low-pressure penstock, water |
| CC12 | A36 / A283 | 36 | General low-pressure |
| CC20 | A283 Gr.C / A516 Gr.55 | 55 | Water mains, penstock |
| CC21 | A516 Gr.55 | 55 | Petrochemical low-temp |
| CC22 | A516 Gr.55 | 55 | Moderate-temperature piping |
| CC30 | A516 Gr.60 | 60 | Process piping, refinery |
| CC31 | A516 Gr.60 | 60 | Higher-pressure process |
| CC32 | A516 Gr.60 | 60 | Hot reheat lines |
| CC40 | A516 Gr.70 | 70 | High-pressure service |
| CC41 | A516 Gr.70 | 70 | Power plant main steam |
| CC42 | A516 Gr.70 | 70 | Critical high-temp piping |
| CC50 | A537 Cl.1 | 65 | Heat-treated process |
| CC60 | A537 Cl.2 | 70 | Heat-treated higher-temp |
| CC65 | A537 Cl.2 | 70 | Highest atmo / low-temp service |
Note: A671 Class numbers 10–42 cover normalised plate grades; classes 50–65 require quenched-and-tempered plate for higher strength at lower temperature. Buyers should always confirm the class letter matches the plate MTC and the project’s lowest design metal temperature (LDMT).
3. A672 Class Letter Comparison
A672 class letters follow a similar pattern but use a higher-strength plate family geared to elevated-temperature pressure service.
| A672 Class | Plate Spec | Min Tensile (ksi) | Typical Service |
|---|---|---|---|
| L65 | A516 Gr.65 | 65 | Moderate-pressure process |
| L70 | A516 Gr.70 | 70 | High-pressure process, feedwater |
| L75 | A537 Cl.2 | 75 | High-temperature pressure |
A672 has fewer class options because the specification is tuned for the narrower high-pressure power-piping use case. Each class imposes more stringent weld-procedure qualification, radiographic examination and post-weld heat treatment than the A671 equivalent.
4. Manufacturing Route and Weld Procedure
Both standards permit EFW manufacture using one of three plate-edge preparation and weld sequences:
- Single-weld (Type 1) — one longitudinal DSAW pass on each side of the joint after tack welding.
- Double-weld (Type 2) — two independent welds, each subjected to 100% radiographic examination. Used for the highest class.
- Type 3 — gas-metal-arc root pass plus DSAW filler / cap, common for power piping.
For A671 CC10 through CC42 the standard permits weld procedures qualified per ASME Section IX. For higher classes (CC50, CC60, CC65) and for all A672 classes, the procedure qualification must include Charpy V-notch testing at the lowest service temperature with full-size specimen minimum energy of 13 ft·lbf (18 J) average / 10 ft·lbf (14 J) single specimen.
5. Heat Treatment Requirements
Heat treatment is a key differentiator. A671 pipes built from as-rolled or normalised plate (CC10–CC42) typically receive a stress-relief anneal after welding if the wall thickness exceeds 1-1/4 inch (32 mm) or if the service temperature exceeds 400°F. For A671 CC50, CC60 and CC65, the pipe must be quenched and tempered after welding to achieve the required strength and toughness.
A672 mandates post-weld heat treatment (PWHT) for every class because the elevated-temperature pressure service demands stress-relieved welds and refined HAZ microstructure. PWHT soak temperature typically ranges 1100–1200°F (593–649°C) for one hour per inch of thickness, with controlled heating and cooling rates below 300°F/hr.
6. Inspection and Testing Regime
Both standards require visual and dimensional inspection, hydrostatic test, and either radiographic examination (RT) or ultrasonic testing (UT) of the weld seam. The frequency and acceptance criteria differ by class.
| Test | A671 (typical) | A672 (typical) |
|---|---|---|
| Radiographic examination | Spot RT (per class) | 100% RT for all welds |
| Charpy V-notch | Required for class ≥ 32 and below 0°F | Mandatory at design temperature |
| Hardness | Optional, requested for sour service | Required on weld + HAZ after PWHT |
| Hydrostatic | Required | Required at higher test pressure |
| MTC EN 10204 | 3.1 typical | 3.1 / 3.2 depending on contract |
For critical A672 applications, specify EN 10204 Type 3.2 certification with witnessed inspection by an independent third party such as SGS, BV, TUV or Intertek. This adds cost but provides independent verification of plate traceability, weld-procedure qualification, NDE and final mechanical testing.
7. Applications and Selection
The choice between A671 and A672 ultimately rests on design temperature and pressure:
| Service Condition | Recommended Spec | Common Class |
|---|---|---|
| Water transmission, penstock | A671 | CC20 / CC21 / CC30 |
| Low-temperature process piping | A671 | CC32 / CC40 / CC42 |
| Atmospheric tank shells | A671 | CC10 / CC11 |
| Offshore platform piping | A671 | CC40 / CC65 (depending on LDMT) |
| Power plant main steam | A672 | L70 / L75 |
| Refinery hydrocracker piping | A672 | L70 |
| High-temperature reheat lines | A672 | L75 |
| Petrochemical ethylene cracking | A671 (with -50°F impact) or A672 | CC65 / L70 |
If the operating temperature is below 400°F and pressure is moderate, A671 delivers the most cost-effective solution. Above 400°F, especially in power and refinery high-pressure service, A672 is the correct specification. Mixing the two is a common procurement error that can lead to premature failure or over-priced pipe.
8. Frequently Asked Questions
Can A671 pipe be used for high-temperature service?
A671 is designed for atmospheric and lower-temperature service, generally up to about 400°F. Above that temperature, the plate grades do not retain sufficient creep resistance. For high-temperature pressure service use A672.
Is A672 pipe more expensive than A671?
Yes, typically 20–40% higher because of the mandatory PWHT, 100% radiographic examination, and tighter Charpy impact requirements. The premium is justified by the higher design temperature and pressure ratings.
What is the difference between A671 and API 5L for large-diameter line pipe?
API 5L is the standard for oil and gas transmission pipelines, optimised for sour service, HIC and toughness. A671 / A672 are ASTM standards for industrial piping and pressure service. For long-distance pipelines use API 5L; for plant piping use A671 / A672.
Can both standards be welded using the same procedure?
No. The two standards require different weld procedure qualifications because of differing plate families, weld types, and heat-treatment requirements. Each procedure specification (WPS) must be qualified for the specific class and plate combination.
9. Supplementary Requirements and Special Clauses
Buyers can add supplementary requirements to the purchase order for special service conditions:
- Supplementary Requirement S1 (vacuum treatment) — steel shall be vacuum-degassed to limit hydrogen content below 2 ppm. Reduces risk of hydrogen-assisted cracking in sour service.
- Supplementary Requirement S2 (product analysis) — chemical check analysis on each heat. Adds cost but verifies traceability and mill accuracy.
- Supplementary Requirement S4 (additional tension tests) — tensile tests at 0°F or −50°F for sub-zero verification beyond the standard Charpy requirement.
- Supplementary Requirement S6 (Charpy V-notch) — explicit Charpy at a specific temperature for the project, typically −50°F for LNG pre-cooling or −20°F for general low-temp.
- Supplementary Requirement S8 (ultrasonic examination of plate) — UT inspection of the plate before pipe forming to detect laminations and inclusions.
- Supplementary Requirement S11 (controlled cooling) — mandatory accelerated cooling for A672 classes to refine grain structure.
- Supplementary Requirement S12 (weld repair limits) — restricts the depth and frequency of weld repairs to maintain pipe integrity.
Each supplementary requirement adds cost (typically 5–15% per requirement) but materially improves quality assurance for critical service. Always include supplementary requirements on the purchase order — they are not automatic and must be specified.
10. Plate Feedstock Sourcing
The plate used to form A671 / A672 pipe is supplied to ASTM specifications by dedicated plate mills. The most common plate specifications are:
- ASTM A36 — for A671 CC10 / CC11 / CC12 atmospheric pipe. Min yield 36 ksi.
- ASTM A283 Gr.C — for A671 CC20 / CC21 moderate pressure pipe. Min yield 30 ksi.
- ASTM A516 Gr.55 / 60 / 65 / 70 — for A671 CC20 through CC42 and A672 L65 / L70. Pressure vessel quality plate.
- ASTM A537 Class 1 / Class 2 — for A671 CC50 / CC60 / CC65 and A672 L75. Quenched-and-tempered plate.
- ASTM A204 Gr.B / Gr.C — Mo-alloyed plate for higher temperature service.
- ASTM A387 Gr.11 / Gr.22 — Cr-Mo alloy plate for elevated temperature pressure service.
- ASTM A302 Gr.C / Gr.D — Mn-Mo-Ni plate for higher strength at elevated temperature.
Plate certificate (EN 10204 3.1 / 3.2) must accompany the pipe certificate. Verify plate heat number matches the pipe certificate. Mismatched heat numbers are a common cause of pipe rejection at the job site.
11. Cost and Lead Time Considerations
A671 / A672 EFW pipe pricing depends on plate cost, class, diameter, quantity and delivery destination. As a rule of thumb:
- A671 CC20 / CC30 is the most common and lowest-cost option for water and low-pressure service
- A671 CC40 / CC42 adds 10–15% over CC30 for A516 Gr.70 plate
- A671 CC50 / CC60 / CC65 adds 25–40% over CC30 for Q&T plate
- A672 L70 / L75 adds 35–50% over A671 CC30 for PWHT + 100% RT + tighter Charpy
- Sour service (NACE MR0175) adds 5–10% for hardness restriction and documentation
- EN 10204 3.2 adds 3–5% over 3.1 for witnessed inspection
Standard lead time is 60–90 days for mill-run orders of 200–1000 tonnes. Smaller quantities can be sourced from service centers in 15–30 days. Large-diameter pipe (over 48 inch NPS) typically adds 30–60 days due to specialised forming equipment requirements.
Need A671 or A672 EFW pipe for a power, refinery, water or penstock project? Huaxia Steel supplies A671 and A672 pipe from 18 inch to 120 inch NPS, all class options, with full MTC 3.1 / 3.2 and witnessed inspection by SGS / BV / TUV. Email [email protected] with your diameter, wall thickness, class, quantity and delivery destination, and we will respond with a mill-direct quotation within 24 hours.
