الفرق بين أنابيب A671 و A672 EFW

مقدمة

For large diameter industrial piping applications, the two most common standards for Electric Fusion Welded (EFW) pipe are ASTM A671 and ASTM A672, yet their common naming conventions—that is, the same terms are used like “Grade” and “Class”) result is a lot of confusion for engineers and buyers.Although these two standards have close similarities in forming processes and look very similar, they serve very different Engineering intents: One is designed to combat brittleness in cryogenic or extreme low temperature conditions, the other designed withstand extremely high pressure in moderate temperature, which means using the wrong specification can lead to disastrous failure of the pipeline.This article is your one stop shop for a technical explanation (Application Temperature, Parent Plate selection, Heat treatment and Testing requirements) to distinguish between ASTM A671 vs A672 and for you to make the right engineering choice for your critical infrastructure.

Service Temperature

Comparing the titles of the A671 and A672 specifications will give you an idea of what the differences are. The difference is not vague – it is explicitly decided by the operating environment.

ASTM A671 (The Low-Temperature Specialist)

• Full Title:​Standard Specification for EFW Steel Pipe for ​Atmospheric and Lower Temperatures.
• The Engineering Context: This specification is suitable for use when the pipe will be exposed to cold service. As the temperature decreases, steel becomes brittle by nature (the ductile-to-brittle transition).EFW steel pipe to A671 is specifically designed to and tested to retain its toughness and avoid fracturing at temperatures from ambient to cryogenic.
• التطبيقات النموذجية: Liquefied gas transmission (LPG/LNG piping), cryogenic pressure vessels, and piping in arctic or sub-zero climates.

ASTM A672 (The Moderate-Temperature Specialist)

• Full Title: Standard Specification for EFW Steel Pipe for ​High-Pressure Service at Moderate Temperatures.
• The Engineering Context: This specification is concerned with the pressure-retaining and structural stability requirements in “moderate” heat. It is not intended for extreme cold, nor for the extreme creep range temperatures covered under ASTM A691 (High Temperature).It sits in the middle tier of most industrial steam and process fluids.
• التطبيقات النموذجية: Steam supply lines, feedstock lines in refineries, and general high-pressure fluid transport where freezing is not a concern.

الخلاصة: Temperature is your number one filter. Where the design temperature is less than 0°C (-32°F) you will need A671. If the design is for high pressure at ambient or medium temperature (up to around 400°C or 750°F), the standard is A672.

Grade: The Parent Plate

Unlike seamless pipes which are defined by their chemical composition as a “pipe” (e.g., A106), EFW pipes are fabricated from ​steel plates​. Therefore, the “Grade” of an A671 or A672 pipe actually refers to the specification of the raw steel plate used to form it.

ASTM A671 Grades (Focus on Toughness)

The grades in A671 are selected for their low-temperature impact properties.

• Common Grade: CC60, CC70.
• The Parent Plate: These typically correspond to ASTM A516 (Pressure Vessel Plates, Carbon Steel, for Moderate- and Lower-Temperature Service).
• Metallurgy: ASTM A516 plate is produced with a fine austenitic grain size. This fine grain structure is essential for maintaining notch toughness (resistance to cracking) at low temperatures.

ASTM A672 Grades (Focus on Strength)

The grades in A672 are selected for tensile strength and pressure retention.

• Common Grade: B60, C70.
• The Parent Plate:
  • Grades A, B, C often correspond to ASTM A285 (Pressure Vessel Plates, Carbon Steel, Low- and Intermediate-Tensile Strength).
  • Grades J, K, L often correspond to ​ASTM A516.
• Metallurgy: While A672 can use the same A516 plate as A671, it can also use simpler carbon steel plates like A285 if low-temperature toughness is not required.

Comparison Table: Pipe Grade vs. Parent Plate Specification

(Note: A671 CC60 vs A672 C70 is a common comparison. While both might use A516 plate, the testing requirements imposed on that plate differ based on the pipe spec.)

Weld Quality & NDT

Perhaps the most confusing aspect of these standards is the “Class” system (e.g., CL12, CL22, CL32). The Class does not indicate the strength of the steel; it indicates the Post-Weld Heat Treatment (PWHT) and the extent of الاختبارات غير المدمرة (NDT) performed on the weld seam.

This is where the manufacturing capability of ألاند becomes critical. As a producer of أنابيب LSAW for pressure vessels, we must strictly adhere to these class designations to ensure the weld seam is as strong as the pipe body.

The Class designation is typically a two-digit number (e.g., ​CL 22​):

1. The First Digit: Indicates the Heat Treatment.

2. The Second Digit: Indicates the Radiography (X-Ray) requirement.

The Heat Treatment Codes (First Digit)

• 10-19: No Heat Treatment required (As-welded).
• 20-29: Stress Relieved (Post-Weld Heat Treatment – PWHT). This reduces internal residual stresses caused by the welding process.
• 30-39: Normalized. The entire pipe is heated to a range where the grain structure recrystallizes, providing the highest level of uniformity.

The Radiography Codes (Second Digit)

• 0: No Radiography.
• 1: Spot Radiography (Sample testing).
• 2:​100% Radiography. (Every inch of the weld seam is X-rayed).
• 3: 100% Radiography + Ultrasonic Testing (UT).

Common Classes Explained

• Class 12: No heat treatment + 100% Radiography.
• Class 22 (The Industry Standard):​Stress Relieved + 100% Radiography. This is the most common specification for high-pressure piping because it ensures the weld is stress-free and physically proven to be defect-free.
• Class 32: Normalized + 100% Radiography. Used when maximum microstructural uniformity is required.

Allland’s Advantage: Manufacturing EFW pipe to Class 22 or Class 32 requires advanced in-house capabilities. ألاند is equipped with large-scale heat treatment furnaces and automated radiographic testing for EFW pipe systems, ensuring we can deliver high-class pipes that meet the strictest pressure vessel codes (ASME BPVC).

Impact Test (The Safety Factor)

The final and definitive difference between ASTM A671 specification and A672 lies in the mandatory testing protocols regarding toughness.

ASTM A671: Mandatory Charpy V-Notch

Because A671 is designed for “Lower Temperatures,” the standard التفويضات that the weld and the Heat Affected Zone (HAZ) must pass the Charpy V-Notch (CVN) impact test.

• Purpose: To quantify the amount of energy the material can absorb before fracturing at low temperatures.
• Requirement: If you order A671 Grade CC60, the manufacturer must prove the pipe stays ductile at the specified low temperature (e.g., -40°C or -50°F).

ASTM A672: Optional Toughness

Because A672 is for “Moderate Temperatures,” brittle fracture is less of a concern.

• Status: Impact testing is generally not mandatory unless specifically requested by the purchaser in the Supplementary Requirements (S2).
• Focus: The testing focus for A672 is on Tensile Strength (transverse weld tension) and Guided Bend tests to ensure the weld can withstand high pressure without separating.

Procurement Insight: If you are operating in a cold climate but specify A672 pipe without adding a supplementary impact test requirement, you are taking a significant risk. Conversely, specifying A671 for a hot steam line may incur unnecessary testing costs.

الخاتمة

The difference between ASTM A671 and ASTM A672 is not just a bureaucratic one, but a matter of thermodynamics that every engineer must face. It is a matter of thermodynamics that every engineer must face. The decision depends solely on the conditions of your service: use ASTM A671 for applications at low temperatures in order to avoid brittle fracture, and use ASTM A672 for services at relatively low temperatures with high pressure. They don’t be confused with each other, it can affect the security of your pressure vessel or piping system.

As a top manufacturer, Allland has advanced LSAW and SSAW production lines, combined with integrated heat treatment and NDT facilities to process EFW pipes as per both the standards. Whether you’re looking for the low temperature toughness of A671 CC60 CL22 or the high pressure stability of A672 C70 CL32, we can supply. Get in touch with Allland today to talk about your individual EF welded pipe application requirements and get a cost-effective, standards-compliant quote.