ASTM A672 covers electric fusion welded steel pipe for high pressure service at moderate temperatures. The C70 grade and the CL22 class together describe a carbon manganese pipe with a 70 ksi minimum tensile strength level and a demanding set of manufacturing, inspection, and testing requirements. EFW pipe of this class is a practical alternative to seamless when large diameters are needed, because the weld is made from plate with controlled chemistry and full volumetric examination.
Understanding the C70 CL22 Designation
The C70 portion of the designation refers to the strength level of the steel, with a minimum yield strength of 485 MPa or 70 ksi and a tensile range of 485 to 620 MPa. The CL22 class specifies the manufacturing and inspection grade: pipe in Class 22 is produced with the weld seam formed by electric fusion welding and is subject to heat treatment and non-destructive examination in line with the standard. The combination means the pipe is suitable for pressure service where a welded seam is acceptable and where carbon steel properties meet the design conditions.
Chemical Composition
| Element | CC70 / C70 Grade Limit, percent |
|---|---|
| Carbon | 0.27 max |
| Manganese | 0.79 to 1.30 |
| Phosphorus | 0.035 max |
| Sulfur | 0.035 max |
| Silicon | 0.13 to 0.45 |
The carbon manganese system is kept within tight limits so the base plate and the weld both reach the required strength without sacrificing weldability. The phosphorus and sulfur caps control inclusions and keep the weld zone clean, which matters for hydrostatic and non-destructive testing.
Mechanical Properties
| Property | Requirement |
|---|---|
| Yield strength | 260 MPa minimum |
| Tensile strength, base metal | 485 to 620 MPa |
| Elongation | 21 percent minimum |
| Weld tensile strength | 485 to 620 MPa |
The tensile requirements apply to the base metal, and a transverse weld tensile test confirms that the seam is at least as strong as the plate. This weld strength verification is one of the reasons EFW pipe is accepted in pressure systems where ERW pipe might not be permitted.
Manufacturing and Heat Treatment
C70 CL22 pipe is formed from plate into a cylinder, then the longitudinal joint is closed by submerged arc welding or electrofusion welding. After welding, the pipe is heat treated as required by the class, with normalizing the common route for this strength level. The heat treatment restores the heat affected zone and guarantees the full strength and toughness of the weld area. Finished pipe is hydrostatically tested and the seam is examined by radiography or ultrasonic methods per the standard.
Applications by Industry
CL22 pipe is engineered for medium and high pressure, non-extreme temperature service. In refineries it appears in hydrodesulfurization unit piping and ethylene plant steam lines. Power plants use it for boiler feedwater piping and waste heat recovery systems. Fertilizer plants specify it for syngas compressor piping, and air separation units use it for medium pressure nitrogen transfer lines. In every case the design pressure stays within the carbon steel envelope and the temperature stays below the point where creep governs the design.
FAQ
What does CL22 mean in ASTM A672?
CL22 is the class designation for electric fusion welded pipe with specified heat treatment and testing requirements. The class controls how the pipe is manufactured, inspected, and tested beyond the base grade requirements.
Is A672 C70 CL22 pipe seamless or welded?
It is welded pipe. The longitudinal seam is formed by electric fusion welding, typically submerged arc welding, from formed plate. Seamless is not part of the A672 product form.
What is the difference between A672 and A671 pipe?
Both are electric fusion welded pressure pipe standards. A671 covers carbon steel pipe based on specified strength levels, while A672 covers pipe whose composition and properties are tied to a specific base material specification.
Can C70 CL22 pipe be used above 400 degrees Celsius?
The standard is intended for moderate temperature service. Above the carbon steel temperature limit, creep strength is not guaranteed and a chromium molybdenum grade should be selected.
What tests are mandatory for CL22 pipe?
Mandatory tests include tensile tests on the base metal and the weld, hydrostatic testing of each length, and non-destructive examination of the weld seam. Additional tests can be agreed with the buyer.
What sizes are available in C70 CL22 EFW pipe?
Because the pipe is formed from plate, diameters typically start around 400 mm and extend to 2500 mm or more, with wall thicknesses from about 6 mm up to 50 mm depending on the plate available.
