Arc Welding 101: Sorting out SAW

Q: What is the procedure qualification test for manufacturing pipe using submerged arc welding?

A: Pipe is manufactured by one of these four methods: electric resistance welding (ERW)/high-frequency induction (HFI) welding, seamless (plug/mandrel mill and extrusion), spiral welding, and longitudinal welding. Spiral and longitudinal welds typically are made by the submerged arc welding (SAW) process.

Ends of a formed section of plate, referred to as skelp, are brought together to form a butt joint. When pipes exceed 36 inches in diameter, two sections of skelp are brought together and joined with two butt joints 180 degrees to each other. These sections are typically 40 feet long.

The welding process consists of one or more electrodes (most likely three) under a blanket of granular flux. The electrodes can be AC, DC, or a combination of the two.

Procedure qualification would require running a test sample in the flat position (1G) on like material with a wall thickness of either 3/8 or 1 in., depending on the wall thickness of the pipe being manufactured.

The completed test sample needs to be visually acceptable; nondestructively tested, usually by radiograph; destructively tested through reduced section testing (a minimum of two specimens); and the root, face, or side bend-tested (minimum four specimens). Depending on the specific code requirements, the test sample may also require Charpy V-notch testing.

All these test types—visual, nondestructive, and destructive—must be found acceptable, and the manufacturing process needs to duplicate the testing process within acceptable tolerances.

The SAW process is used because of its efficiency, high deposition rates, deep penetration, and overall clean appearance. The specifics of the SAW process differ from producer to producer and with material composition and thickness, and are usually a producer’s closely guarded secret.

To research SAW in detail, refer to The Procedure Handbook of Arc Welding, 14th edition. It is available from The Lincoln Electric Company.