ASTM A671 CC70 CL22 EFW Steel Pipe: Manufacturing & Specifications

Because CC70 is tied to A516 Gr.70 plate, the finished pipe’s chemistry and strength follow that plate standard.

Actual test results on the mill certificate reflect the specific heat and plate used. Class 22 stress relieving does not alter the base chemistry. For projects requiring impact testing, Charpy V-notch testing can be specified as a supplementary requirement.

Grade Comparison: CC60 vs CC65 vs CC70

The three grades share the same manufacturing route and Class 22 options; the difference is the base plate strength level. CC70 is the highest strength grade in the CC series.

For a given design pressure and temperature, the allowable stress increases from CC60 to CC70. CC70 is often selected when the design pressure is high enough that the wall thickness savings from the higher allowable stress offset the higher plate cost, or when the required wall thickness with CC60 or CC65 would exceed rolling or welding capability.

Class 22 vs Other A671 Classes

Class 22 is the common choice when the pipe will see low ambient or process temperatures and the weld seam must be fully examined. Class 32 is specified when the design requires normalized plate properties in the finished pipe. Class 42/52 are reserved for more severe toughness or thickness combinations.

Size Range and Manufacturing Options

Womic produces A671 CC70 CL22 pipe using LSAW with either single straight seam or double straight seam configuration.

ASTM A671 nominally covers pipe 16 inches (400 mm) outside diameter and larger with wall thickness of 1/4 inch (6 mm) or greater. Pipe outside this nominal range can be supplied if it meets all other requirements of the specification.

Single Straight Seam vs Double Straight Seam

Single straight seam is used when one plate can be rolled into a full cylinder. At Womic this covers OD up to about 1,422 mm with wall thickness up to 50.8 mm on the JCOE line. There is one longitudinal weld, so weld inspection coverage is concentrated on a single seam, and production is more economical for standard sizes.

Double straight seam is used when the diameter or wall thickness exceeds what a single plate can form. Two plates are rolled into half-cylinders and each is welded longitudinally. This covers OD from about 1,200 mm to 2,540 mm with wall thickness up to 80 mm. The trade-off is two weld seams to inspect and more welding time, but it enables large-diameter and heavy-wall pipe that single seam cannot produce.

For a given project, the mill selects the seam configuration based on the ordered size. If the project specification restricts the seam type, state this in the purchase order.

Welding and Heat Treatment

The longitudinal seam is welded by multi-wire submerged arc welding, with one pass on the inside and one or more passes on the outside. Filler wire and flux are selected to match the A516 Gr.70 base metal and to produce weld metal with chemistry and toughness compatible with the plate. After welding, the pipe is stress relieved per Class 22 requirements: heated uniformly to a temperature below the critical range, held for a time proportional to wall thickness, and cooled in a controlled manner.

For CC70, the higher carbon and manganese content relative to CC60 requires attention to welding procedure qualification, particularly for heavy wall thickness where heat input and cooling rate affect the weld metal and heat-affected zone toughness.

What Class 22 Testing Involves

Stress Relieving: After welding, the pipe is heated to a temperature below the critical range and held to relieve residual stresses from forming and welding. This matters for pipe that will be further fabricated or subjected to thermal cycling in service.

Radiographic Examination: The longitudinal weld seam is examined by X-ray or gamma ray to detect internal defects such as porosity, slag inclusion, or lack of fusion. The extent of radiography follows the A671 requirements for Class 22.

Hydrostatic Testing: Each pipe is filled with water and pressurized to a level determined by the specified wall thickness and diameter, held for a defined period, and inspected for leaks or permanent deformation.

Supplementary requirements in ASTM A671 can be invoked for impact testing, additional radiography, or other examinations when the project demands more than the base Class 22 scope.