ASTM A671 EFW Steel Pipe: Complete Grade Guide for Atmospheric and Low-Temperature Pressure Service

A671 Grade Series: CA, CB, and CC

A671 grades are designated by a two-letter series followed by a two-digit number. The letter series identifies the base plate specification, and the number identifies the strength level within that specification.

The CC series is the most widely specified in low-temperature pressure service because A516 plate is killed and fine-grain, with good notch toughness at low temperature. The CA and CB series are used where the pressure and temperature are less demanding and the economics favor the lower-grade plate.

A671 CC Series Grade Progression: CC60 to CC70

The CC series is the core of the A671 low-temperature offering. The three grades share the same manufacturing route and class options; the difference is the base plate strength level.

For a given design pressure and temperature, the allowable stress increases from CC60 to CC70. Selection depends on the design code’s allowable stress tables at the operating temperature and on whether the wall thickness savings from the higher grade offset the higher plate cost.

A671 CA and CB Series

The CA and CB series are also covered by A671 and are available on request. They are less common in low-temperature pressure service than the CC series but are specified where the design conditions permit a lower-grade plate.

The CA and CB grades do not carry the fine-grain and low-temperature toughness characteristics of A516 plate, so they are not typically specified for service where Charpy impact testing at low temperature is required. For low-temperature service, the CC series is the appropriate choice.

The A671 Class System

The class designation controls heat treatment, radiography, and pressure testing. Class 22 is the most commonly specified class for low-temperature pressure service because it combines stress relieving, full RT, and hydrostatic testing.

Class 22 is the workhorse class for A671 CC series pipe. Class 32 is specified when the design requires normalized plate properties in the finished pipe, which can be important for thicker wall or more demanding toughness requirements. Class 42/52 are reserved for more severe toughness or thickness combinations.

Size Range Across the A671 Family

Womic produces A671 pipe in all the grades listed above using LSAW with single or double straight seam configuration.

Single Straight Seam vs Double Straight Seam

Single straight seam covers OD up to about 1,422 mm with wall thickness up to 50.8 mm on the JCOE line. One longitudinal weld concentrates inspection on a single seam.

Double straight seam covers OD from about 1,200 mm to 2,540 mm with wall thickness up to 80 mm. Two plates are rolled into half-cylinders and each is welded longitudinally. The trade-off is two weld seams to inspect, but it enables large-diameter and heavy-wall pipe that single seam cannot produce.