1. What is ASTM A672 steel pipe primarily used for?
ASTM A672 is a standard specification for electric-fusion-welded (EFW) carbon and alloy steel pipes designed for high-temperature and high-pressure service. Its primary applications include power generation (boiler systems, steam lines), industrial process piping (refineries, chemical plants), and pressure vessel components. The pipe is engineered to withstand elevated temperatures (up to 1,000℃F/538℃ depending on the grade) and internal pressures, making it suitable for critical fluid transport where reliability under harsh conditions is essential.
2. What material grades are covered under ASTM A672?
ASTM A672 classifies pipes into multiple grades based on chemical composition and mechanical properties, with the most common being:
Grade C: Carbon steel (minimum yield strength: 30 ksi/207 MPa) for general high-temperature service.
Grade B: Low-alloy steel with chromium and molybdenum (Cr-Mo) additions, offering enhanced creep resistance at elevated temperatures.
Grade P91/P92: High-alloy Cr-Mo-V grades (9% Cr, 1% Mo, V) for ultra-high-temperature applications (e.g., advanced power plants).
Each grade is further differentiated by wall thickness and diameter ranges, as specified in the standard.
3. What welding process is required for ASTM A672 pipe?
ASTM A672 mandates electric fusion welding (EFW), which includes processes such as:
Submerged Arc Welding (SAW): Most common for large-diameter pipes (>=16 inches/406 mm) due to high efficiency and consistent weld quality.
Gas Metal Arc Welding (GMAW/MIG): Used for smaller diameters or field installations.
The standard requires welds to undergo non-destructive testing (NDT), including radiography (RT) or ultrasonic testing (UT), to ensure no internal defects (e.g., cracks, porosity) that could compromise structural integrity under pressure.
4. What are the key mechanical properties of ASTM A672 pipe?
Yield Strength (YS): 30–60 ksi (207–414 MPa) depending on the alloy content.
Tensile Strength (TS): 60–90 ksi (414–621 MPa).
Elongation: Minimum 20% in 2 inches (50 mm) to ensure ductility.
Impact Resistance: Charpy V-notch (CVN) testing at specified temperatures (e.g., -20℃F/-29℃ for low-temperature service) to prevent brittle fracture.
These properties are verified through destructive testing of production samples per ASTM A672.
5. What size and thickness ranges does ASTM A672 cover?
ASTM A672 specifies:
Diameters: From 6 inches (152 mm) to 64 inches (1,626 mm) (nominal pipe size, NPS).
Wall Thickness: From Schedule 10 to Schedule 160, plus extra-heavy (XH) and double extra-heavy (XXH) thicknesses, corresponding to 0.312 inches (7.9 mm) to 4.000 inches (101.6 mm).
Lengths: Typically 20 feet (6.1 m) or 40 feet (12.2 m) for standard delivery, with custom lengths available upon request.
The standard also includes tolerances for diameter, wall thickness, and straightness to ensure compatibility with fittings and installation requirements.
