What Is A672 C70 Pipe
A672 C70 steel pipe is a low-alloy high-strength electric fusion welded (EFW) steel pipe intended for medium- to high-temperature and high-pressure pipeline systems. It belongs to the ASTM A672 specification for electric-fusion-welded steel pipe for high-pressure service at moderate and lower temperatures, and the C70 designation refers to a carbon-manganese-silicon steel with controlled composition. The pipe is formed from steel plate and welded with a longitudinal seam using submerged arc welding, which gives it the strength and integrity required for demanding energy and chemical applications.
Chemical Composition
The base material is a low-carbon manganese-silicon alloy steel. Carbon is strictly controlled at 0.22 percent maximum, which is tighter than the general limit for many A672 grades and improves weldability and toughness. Manganese is added at 1.00 to 1.60 percent and silicon at 0.15 to 0.40 percent to balance strength and toughness, and trace elements such as niobium and vanadium are used for microalloy strengthening. Phosphorus and sulfur are limited to 0.025 percent maximum each, which significantly improves resistance to brittle fracture at low temperature. The steel is typically vacuum degassed to reduce gas content and improve homogeneity.
Mechanical Properties
| Property | Requirement |
|---|---|
| Yield strength | 485 MPa minimum |
| Tensile strength | 620 MPa minimum |
| Elongation | 18 percent minimum |
| Low-temperature toughness | 27 J minimum at -46 degrees C (Class 22) |
These values give the pipe about 40 percent higher pressure-bearing capacity than ordinary carbon steel pipe, making it suitable for systems operating above 10 MPa. The elongation supports cold bending and welding deformation during fabrication.
Manufacturing Process
The pipe is formed by progressive pressing methods such as JCOE or UOE, which avoid excessive deformation of the material during forming. Multi-wire submerged arc welding (SAW) ensures full weld penetration and density. Heat treatment such as normalizing, quenching, and tempering is applied according to process requirements to eliminate welding stress and refine the microstructure. The combination of controlled forming, high-integrity welding, and heat treatment produces a pipe with consistent mechanical properties across the seam and base metal.
Typical Applications
Energy: high-pressure feed water piping in supercritical power plant boilers, and low-temperature transmission lines for LNG storage. Chemical and oil and gas: gathering and transmission lines for sour oil and gas service, and high-pressure circulation systems in chemical reactors. The low-temperature toughness of the Class 22 designation supports service in polar and deep-sea environments.
Frequently Asked Questions
Q: What does C70 mean in ASTM A672?
A: C indicates a carbon-manganese-silicon steel class, and 70 refers to the strength level of the material. The designation follows the mechanical property requirements defined in ASTM A672.
Q: Is A672 C70 pipe seamless or welded?
A: A672 is an electric fusion welded (EFW) specification. The pipe is formed from steel plate and welded longitudinally, typically by submerged arc welding on both sides.
Q: What is the minimum yield strength of A672 C70?
A: The minimum yield strength is 485 MPa, with a minimum tensile strength of 620 MPa and minimum elongation of 18 percent.
Q: What temperature can A672 C70 withstand?
A: The material is designed for medium- to high-temperature service up to about 480 degrees C in boiler feed water duty, and the Class 22 low-temperature designation provides 27 J impact energy at -46 degrees C.
Q: How is A672 C70 pipe tested?
A: Testing includes chemical analysis, tensile tests, and Charpy impact tests for the low-temperature class, plus hydrostatic testing and non-destructive examination of the weld seam.
Q: Can A672 C70 be used for sour service?
A: Yes, with appropriate additional requirements. The low phosphorus and sulfur content and vacuum degassing improve resistance to hydrogen-induced damage, and supplementary testing can be specified for H2S service.
For a quotation on A672 C70 pipe with your required size, class, and testing requirements, contact our sales team.
