Overview
A672 is an American Standard from ASTM International (formerly the American Society for Testing and Materials). Its full title is "Standard Specification for Electric-Fusion-Welded Steel Pipe for High-Pressure Service at Moderate Temperatures."
The "LSAW" (Longitudinal Submerged Arc Welding) part is crucial. It specifies the manufacturing process used to create the pipe. While the ASTM A672 standard can, in theory, cover other electric fusion welding processes, it is most commonly associated with LSAW pipe for large diameters.
Key Characteristics of A672 LSAW Pipe
Manufacturing Process (LSAW):
Steel plates (skelp) are first formed into a U-shape and then an O-shape (hence the name "UOE" pipe: U-ing, O-ing, Expanding).
The longitudinal seam is welded on the inside and outside using the Submerged Arc Welding (SAW) process. This creates a strong, reliable, and continuous weld.
This process is ideal for producing large-diameter pipes (typically from 16 inches up to over 60 inches) with thick walls.
Purpose and Service:
High-Pressure Service: Designed to convey fluids or gas under significant internal pressure.
Moderate Temperatures: Generally intended for service temperatures up to 800°F (425°C). For higher temperatures, other specifications like ASTM A691 would be more appropriate.
Heat Treatment:
A key feature of A672 pipe is that it is always supplied in the heat-treated condition. The specific type of heat treatment (e.g., stress-relieved, normalized, or quenched and tempered) is designated by a "Class" suffix (e.g., A672 Grade B Class 13, where "13" signifies quenched and tempered). This ensures the mechanical properties are uniform and the residual stresses from welding are relieved.
Standard Grades and Classes
The specification includes several grades based on chemical composition, with multiple classes based on heat treatment and mechanical properties.
Grades: Defined by the chemical composition of the steel. Common grades include:
Grade A: Carbon Steel
Grade B: Carbon-Manganese Steel
Grade C: Carbon-Manganese Steel (higher Mn than B)
Grades D through H: Various low-alloy steels (e.g., with additions of Chromium, Nickel, Molybdenum).
Classes: Defined by the specified minimum yield strength (SMYS) and the heat treatment process. The class number is often the SMYS in ksi (kips per square inch). For example:
Class 12: 30,000 psi min yield strength (205 MPa)
Class 13: 35,000 psi min yield strength (240 MPa)
Class 42: 42,000 psi min yield strength (290 MPa)
Class 45: 45,000 psi min yield strength (310 MPa)
Class 50: 50,000 psi min yield strength (345 MPa)
Class 55: 55,000 psi min yield strength (380 MPa)
Class 60: 60,000 psi min yield strength (415 MPa)
Class 65: 65,000 psi min yield strength (450 MPa)
A common specification would look like: ASTM A672 Grade B Class 45 (A carbon-manganese steel pipe, heat-treated to a minimum yield strength of 45,000 psi).
Typical Applications
A672 LSAW pipes are used in critical high-pressure applications where reliability is paramount:
Pipeline Transmission Lines: For oil and natural gas, both onshore and offshore.
Power Plants: For high-pressure feedwater lines, condenser tubes, and other process piping systems.
Petrochemical Plants: In process lines requiring high strength and pressure resistance.
Water Transmission: For large-diameter, high-pressure water mains.
Comparison with Other Pipe Standards
| Feature | ASTM A672 (LSAW) | ASTM A53 (ERW / SSAW) | API 5L (PSL1 / PSL2) | ASTM A106 (Seamless) |
|---|---|---|---|---|
| Process | Longitudinal Submerged Arc Weld | Electric Resistance Weld / Spiral SAW | Seamless, ERW, HFI, DSAW | Seamless (hot-finished) |
| Common Size | Large Diameter (16" and above) | Small to Large Diameter | Full range | Small to Medium Diameter |
| Key Purpose | High-Pressure, Moderate Temp | General Purpose, Low/Med Pressure | Hydrocarbon Transmission | High-Temperature Service |
| Strength Levels | Multiple Classes (e.g., Class 45, 55) | Grade A & B | Grades B to X80 | Grade A, B, C |
| Cost | Medium-High (plate-based process) | Low (A53) to Medium (LSAW) | Varies by type and grade | High |
Summary
In short, ASTM A672 LSAW steel pipe is a high-quality, large-diameter pipe manufactured from steel plate with a longitudinal submerged arc weld. Its mandatory heat treatment and rigorous testing make it a premium product specified for demanding high-pressure applications in the power generation, petrochemical, and pipeline industries. When you see "A672," you know it refers to a heat-treated, longitudinally welded pipe for critical service.
