ASTM A671/A672

USED FOR:

Electric-fusion-welded steel pipe for atmospheric and lower/higher temperature service, respectively.

A671 covers electric-fusion-welded carbon and alloy steel pipe for atmospheric and lower-temperature service, while A672 covers electric-fusion-welded carbon steel pipe for high-pressure service at moderate temperatures, Both standards define requirements for welded pipe classes associated with weld examination and quality requirements. The applicable design code determines how weld quality factors are applied in pressure design calculations.

RELATED STANDARDS:

• Sibling specs: ASTM A358 covers the equivalent EFW product form but for austenitic stainless steel rather than carbon/alloy steel, same joint-class logic, different base metal. ASTM A155 is an older specification for electric-fusion-welded steel pipe. ASTM A671 and A672 are separate specifications developed for specific service conditions and product requirements. ASTM A53/A106 cover seamless and smaller-diameter welded carbon steel pipe and are used instead of A671/A672 once diameters fall within economical seamless or standard ERW ranges, which is the primary reason A671/A672 exist, to cover large-diameter pipe outside that range.
• Design code that invokes it: ASME B31.3 (process piping) and ASME B31.1 (power piping) both reference A671 and A672 for large-diameter, plate-rolled pipe, and application with ASME Section VIII shall be verified against the applicable vessel construction requirements, material acceptance criteria, and permitted materials listed in the relevant ASME BPVC sections.
• Dimensional standard that pairs with it: ASME B36.10M defines OD and wall thickness/schedule data where standard schedules apply, though A671/A672 pipe is frequently manufactured to non-standard, project-specific diameters and wall thicknesses given its large-bore, plate-rolled nature, this is more common here than with most other pipe specs.

GRADE / TYPE RANGE:
A671 covers a range of carbon steel and low-alloy grades (e.g., CA, CB, CC series for carbon steel, CD, CE for low-alloy chrome-moly) intended for lower-temperature and atmospheric service, with grade selection driven mainly by design temperature and the need for impact toughness at low temperature in some grades.

A672 covers electric-fusion-welded carbon steel pipe manufactured from pressure-vessel-quality plate grades specified by the standard, with requirements based on material grade, class, type, and heat treatment condition. intended for higher design pressures at moderate temperatures, with correspondingly higher tensile/yield strength requirements than the equivalent A671 grades.

In both standards, alloy content increases (chromium-molybdenum additions) as temperature service class increases, following the same general logic as A335, while the differentiator between A671 and A672 specifically is design pressure/stress level rather than temperature alone, A672 grades are generally selected when higher hoop stress design is required at a given diameter.

As with other EFW standards, the joint Class (RT extent) selection has as much practical effect on required wall thickness as the base grade does.

DESCRIPTION:
Both standards cover pipe manufactured by forming rolled plate and welding it longitudinally (or helically, depending on process) using an electric-fusion-welding process, typically followed by stress relief or normalizing heat treatment depending on grade and thickness.

Both standards define different classes based on weld examination and testing requirements. The applicable design code shall be used to establish the weld joint efficiency factor for pressure design calculations.

Testing requirements include tensile testing, and depending on grade, impact testing (particularly relevant for A671 grades intended for lower-temperature service) and hydrostatic or equivalent NDE testing of the completed pipe. Marking requirements identify manufacturer, grade, class, and heat number, with class again carrying direct design consequence and requiring careful traceability similar to A358.

TYPICAL INDUSTRY USE:
Large-diameter piping in refineries, petrochemical plants, and power generation facilities, particularly large process gas lines, large-bore steam lines, and vessel nozzle/shell extensions where diameters exceed what’s economical to produce as seamless pipe.

IMPORTANT NOTES:

• We often see A671 and A672 confused with each other on requisitions since both cover the same general product form (large-diameter EFW carbon/alloy pipe). ASTM A671 and ASTM A672 shall be selected based on the applicable service conditions, material requirements, design temperature, pressure, and project specification. They are not interchangeable solely based on pressure level, and getting this backwards on a large-bore line can mean the wrong wall thickness assumption baked into early design.

• As with A358, the RT Class assumed in the stress/wall-thickness calculation must match what’s actually procured, we always confirm this explicitly with design engineering before accepting mill documentation, since under-specifying the class (or the mill defaulting to a lower class) is a common and costly procurement mismatch on large-bore lines.

• Impact testing supplements are particularly relevant for A671 grades used in lower-temperature or cold-climate service, we recommend confirming MDMT requirements against the specific grade’s impact qualification, since not all A671 grades carry the same low-temperature toughness qualification as standard.

• NACE MR0175/ISO 15156 qualification is not inherent to either standard and must be verified separately (hardness, chemistry) if the line is in sour service, this is worth flagging specifically on large-diameter refinery process gas lines where sour service and large bore frequently coincide.

• Given the large-diameter, often project-specific nature of A671/A672 pipe, we typically see longer delivery times, limited supplier pools, and more project-specific (rather than off-the-shelf) manufacturing, this is worth building into schedule planning early, since these items often become long-lead, engineered-to-order components rather than stock material.