Overview of ASTM A671 CC70 Class 71 Pipe
ASTM A671/A671M is the specification for electric-fusion-welded steel pipe made from pressure-vessel-quality plate, intended for high-pressure service at atmospheric and lower temperatures. The pipe is formed from plate and welded with a double-sided submerged arc weld, then heat treated and examined according to the class. It is produced in large diameters, normally 16 in, about 406 mm, and larger.
The designation CC70 Class 71 has two independent parts. CC70 names the plate material and its strength level: the pipe is made from A516/A516M Grade 70 plate, a killed fine-grain carbon steel. Class 71 names the heat treatment and examination requirements applied to the finished pipe. Each part is explained below.
What the Grade Means
In the A671 designation the two-letter prefix identifies the pressure-vessel plate specification from which the pipe is made, and the number states the minimum tensile strength in ksi. The grade CC70 therefore means pipe made from A516/A516M Grade 70, with a minimum tensile strength of 70 ksi, about 485 MPa.
| Grade | Plate specification | Steel type | Minimum tensile strength |
|---|---|---|---|
| CC70 | A516/A516M Grade 70 | killed fine-grain carbon steel | 70 ksi, about 485 MPa |
CC70 is made from A516 Grade 70, the highest strength member of the A516 fine-grain carbon steel family. The plate tensile range is 70 to 90 ksi, and the fine-grain practice supports good toughness in moderate and lower temperature service.
In terms of strength, The minimum yield strength of the plate is 38 ksi, about 260 MPa..
How the A671 Class System Works
The class is a two-digit code. The first digit selects the heat-treatment family applied to the pipe after welding.
| Class family | Heat treatment applied to the pipe |
|---|---|
| 10 to 13 | None; delivered as welded |
| 20 to 23 | Stress relieved after welding |
| 30 to 33 | Normalized |
| 40 to 43 | Normalized and tempered |
| 50 to 53 | Quenched and tempered |
| 70 to 73 | Quenched and precipitation heat treated |
The second digit selects the examination level.
| Last digit | Radiography of the weld | Pressure test |
|---|---|---|
| 0 | Not required | Not required |
| 1 | Full-length radiography of each weld per ASME VIII UW-51 | Not required |
| 2 | Full-length radiography of each weld per ASME VIII UW-51 | Required per A530/A530M |
| 3 | Not required | Required per A530/A530M |
What Class 71 Means for This Pipe
Class 71 has two digits. The first digit 7 selects the heat-treatment family, which means the pipe is quenched and precipitation heat treated after welding. The second digit 1 selects the examination level, which means every longitudinal weld must be fully radiographed in accordance with ASME Boiler and Pressure Vessel Code Section VIII, UW-51, while no hydrostatic test is required by the class.
Taken together, Class 71 pipe is the pipe is quenched and precipitation heat treated after welding, and every longitudinal weld must be fully radiographed in accordance with ASME Boiler and Pressure Vessel Code Section VIII, UW-51, while no hydrostatic test is required by the class. These requirements are fixed at the time of ordering, recorded on the order documents and confirmed on the mill test certificate.
A516 grades respond well to normalizing, so classes in the 20 to 43 range are common; classes in the quenched families should be confirmed with the mill.
Typical Applications
CC70 pipe is used for high-pressure storage, pressure vessels and lower temperature piping where the 70 ksi tensile level of the A516 family is required with fine-grain notch toughness.
Manufacturing, Testing and Documentation
A671 pipe starts as pressure-vessel-quality plate supplied under the applicable plate standard. The plate is formed into a cylinder and the longitudinal seam is welded by the submerged arc process from both the inside and the outside, producing a full-penetration weld. After welding, the pipe receives the heat treatment of the selected class and then the examination and tests required by the class and by A671/A671M.
Testing normally includes chemical analysis of the heat, tensile testing, and the radiography and hydrostatic pressure tests required by the class. Charpy V-notch impact testing is performed when the design code or the purchase order requires it, and the plate may be ultrasonically examined under A435 or a supplementary requirement. Every pipe is traceable to its plate heat number, and the mill test certificate records the chemical analysis, mechanical test results, heat treatment details and examination results.
The available outside diameters, wall thicknesses and lengths depend on the plate widths and the forming and welding capability of the producing mill, so the required OD, wall, length and end finish should be confirmed with the supplier before ordering.
FAQ
Q1. What does the grade CC70 mean in the A671 designation?
The two-letter prefix identifies the plate specification, and the number states the minimum tensile strength in ksi. CC70 means pipe made from A516/A516M Grade 70 plate, a killed fine-grain carbon steel, with a minimum tensile strength of 70 ksi, about 485 MPa.
Q2. What does Class 71 mean?
Class 71 is read in two digits: the first digit selects the heat-treatment family, the pipe is quenched and precipitation heat treated after welding, and the second digit selects the examination level, which means every longitudinal weld must be fully radiographed in accordance with ASME Boiler and Pressure Vessel Code Section VIII, UW-51, while no hydrostatic test is required by the class.
Q3. What is the minimum tensile strength of CC70 pipe?
70 ksi, about 485 MPa. The number in the grade name states this value directly; it is a tensile value, not a yield value. The minimum yield strength of the plate is 38 ksi, about 260 MPa.
Q4. Does Class 71 define a service temperature?
No. A class defines heat treatment and examination only, never a service temperature. The safe operating temperature is set by the plate material, the impact test requirements and the governing design code; for the CC70 grade, the steel family and its qualified toughness determine the low-temperature limit.
Q5. What tests are performed on A671 pipe?
Every heat is verified by chemical analysis and tensile testing. The class determines whether full-length radiography of the longitudinal weld and a hydrostatic pressure test are required. Charpy impact testing, ultrasonic examination of the plate and other supplementary tests are added when the design code or the purchase order specifies them, and all results are reported on the mill test certificate.
Q6. How is A671 pipe manufactured and what sizes are available?
A671 pipe is formed from pressure-vessel-quality plate and welded with a double-sided submerged arc weld, then heat treated and examined per the class. It is produced in outside diameters of 16 in, about 406 mm, and larger, with wall thicknesses selected for the design pressure and lengths typically supplied in single or double random. Exact availability depends on the producing mill and must be confirmed before ordering.
