What Is ASTM A671 CB65 Class 70 Pipe?
ASTM A671 CB65 Class 70 pipe is an electric-fusion-welded (EFW) steel pipe produced from pressure-vessel-quality carbon steel plate with filler metal added at the longitudinal seam. It belongs to the ASTM A671/A671M family, the specification that covers EFW pipe for atmospheric and lower-temperature service, and is ordered where a welded pipe must combine heavy wall, large diameter and dependable notch toughness below ambient temperature.
In the A671 designation the letter group and the two-digit number together describe the steel. The number sets the minimum tensile strength level in ksi, so a CB65 grade is a 65 ksi (448 MPa) minimum tensile product, while the letter group fixes the heat-treatment and impact-testing route under which the pipe is produced. The class entry, in this case Class 70, is taken from the ordering table of the specification and identifies the plate material and test condition selected by the purchaser.
Because the pipe is welded with filler metal rather than being a seamless product, the specification controls the weld in detail: the seam is made under a qualified welding procedure, examined by radiographic or ultrasonic means, and the finished pipe is hydrostatically tested, so that the seam acts as part of the pressure boundary rather than a weak point.
Grade, Class and Test Requirements
| Item | Requirement |
|---|---|
| Specification | ASTM A671/A671M, EFW pipe for atmospheric and lower temperatures |
| Grade | CB65, minimum tensile strength level 65 ksi (448 MPa) |
| Class | Class 70, plate material and test condition from the A671 ordering table |
| Product form | Pipe formed from plate, welded with filler metal, single or double welded seam |
| Impact testing | Charpy V-notch testing as required for the ordered grade and test temperature |
| Weld examination | Radiographic or ultrasonic examination of the longitudinal seam |
| Pressure test | Hydrostatic test per the specification unless otherwise ordered |
| Heat treatment | As-welded, stress-relieved or normalized condition as ordered |
| Ends and lengths | Plain, beveled or otherwise prepared ends per the purchase order |
The governing acceptance values are the tensile requirements tied to the 65 grade level, the impact energy required at the selected test temperature, and the soundness of the weld. Purchasers should state the impact test temperature together with the grade and class, because the notch-toughness requirement is tied to the temperature at which the test is carried out.
Manufacturing and Weld Quality Control
Plate is cut, edged and rolled to the ordered diameter; the longitudinal edges are then prepared and welded with filler metal. After welding, the pipe passes dimensional checks on outside diameter, wall thickness, out-of-roundness and straightness before the seam is examined.
Radiographic or ultrasonic examination of the full seam is the routine way of demonstrating weld integrity. Where repair is needed, the specification limits its extent and requires the repaired area to be re-examined against the same acceptance criteria. Hydrostatic testing follows, and the test pressure and holding time are recorded together with the chemical and mechanical results on the mill test report.
Applications in Low-Temperature Service
CB65 Class 70 pipe is chosen for pressure piping that operates at atmospheric or lower temperatures: gas processing and cryogenic storage circuits, liquefied gas transfer lines, refrigeration headers and low-temperature sections of process plants where welded heavy-wall construction is more practical than a seamless route.
The large-diameter EFW format suits station piping, headers and equipment connections that need long continuous runs with few girth welds. Low-temperature service is the deciding factor, since the material must retain notch toughness at the design metal temperature, which is why impact testing is written into the order rather than left to the mill.
Ordering, Inspection and Handling Notes
State specification, grade, class, size, wall thickness, length and the required impact test temperature on every enquiry.
Confirm whether radiographic or ultrasonic examination is required and whether a specific method is preferred.
Require test reports traceable to the heat number of the plate and to the welding procedure used for the seam.
Protect beveled ends during transport and store pipe clear of carbon steel debris and standing water.
Handle and stack heavy-wall lengths so that the weld seam never becomes a bearing point.
FAQ
Q: What does the number in ASTM A671 CB65 mean?
It is the minimum tensile strength level in ksi, so 65 designates a 65 ksi (448 MPa) minimum tensile steel, while the class entry identifies the plate and test condition taken from the ordering table.
Q: Is ASTM A671 pipe seamless?
No. A671 pipe is electric-fusion-welded pipe made from plate with filler metal added at the seam; seamless pipe of comparable size is covered by different specifications.
Q: How is the weld examined?
The longitudinal seam receives radiographic or ultrasonic examination as required by the specification, followed by a hydrostatic test of the completed pipe.
Q: What decides the impact test temperature?
The design metal temperature of the application together with the ordered grade. The requirement is stated on the purchase order so the mill tests at the temperature the service demands.
Q: Can the pipe be supplied stress relieved?
Yes. Heat treatment is ordered from the options given in the specification, such as as-welded, stress-relieved or normalized, and the condition is recorded on the test report.
Q: Which sizes are available?
A671 pipe is produced in the large-diameter, heavy-wall range from plate; exact size and wall thickness combinations are confirmed against the ordered dimensions.
