Double Submerged Arc Weld (DSAW)
Submerged Arc Welded (SAW) pipe derives its name from the process wherein the welding arc is submerged in flux while the welding takes place. The flux protects the steel in the weld area from any impurities in the air when heated to welding temperatures. When both inside welds and outside welds are performed, the welding is accomplished in separate processes and the pipe is considered to be Double Submerged Arc Welded (DSAW).
There are three common types of pipe produced by the DSAW process.
---U&O Method
The U&O Method is so called because it first uses a “U”press, then an “O” press to complete cylinder forming from 40’ long plates ordered to size and grade. The cylinder is then welded inside and outside by the submerged arc process by using as many as five welding wires. Most U&O is cold expanded either mechanically or hydraulically. When it is cold expanded, DSAW pipe gains in yield strength. This method of pipe production produces exceptional quality with exact dimensional tolerances. The primary use of this type of pipe is gas and oil transmission. It requires large minimum tonnages for size setup and is only produced domestically in 40-foot lengths.
---Rolled and Welded
This method of manufacturing is also called the “Pyramid Roll Method” because it uses three rolls arranged in a pyramidal structure. The plate, ordered by grade and thickness, is rolled back and forth between the pyramid rolls until the cylinder is formed. The cylinder is then moved to the welding stations. Most pyramid rolls are 20 feet in length or shorter.
Greater lengths are achieved by girth welding the five-foot, 10-foot or 20-foot sections (or cans) together. Berg Steel is the only producer capable of rolling 40-foot plates without a midweld and it is the only producer capable of sizing its product.
Rolled and welded pipe has the advantage of being rolled in small quantities with short lead times. It can be produced in very large diameters, either ID or OD, and in extremely thick walls. Since the cans are short in length, the production of composite piles or pieces varying in yield and tensile are easily attained. The rate of production of this material is slow and the cost is high due to multiple girth welds.
---Spiral Weld
Spiralweld pipe is a steel pipe having a DSAW seam the entire length of the pipe in a spiral form. The outside diameter is determined by the angle of the de-coiled steel against the forming head. The more acute the angle, the greater the diameter. The production of large, hot rolled coils of sufficient width and the development of dependable non-destructive testing methods has enabled this product to be placed in more demanding service.
Spiralweld pipe can be rolled in exact lengths up to 115 feet in either ID or OD dimensions up to
144 inches. There is a minimum tonnage required for rolling. Because the manufacturing process is slow, it gives the contractor an advantage of short term changes to the order. This same slow production can also be a disadvantage when large tonnages are needed with a short lead time. Spiralweld pipe is produced to limited specifications.
