Dyna Torque Technologies, Inc. was recently approached by British Gas/Transco, U.K. to find a solution for the problems encountered when tieing in light-wall to heavy-wall pipe sections. Traditionally, British Gas/Transco used the standard 4 to 1 slope transition bevel for tie-in applications; however, this type of bevel has always presented several problems both from a welding standpoint as well as from a non-destructive testing standpoint. Because the bevel starts the 4 to 1 slope immediately at the joint face, and continues to increase in wall thickness until it is back to the original thickness, the use of ultra sonic testing is at least limited in quality assurance. This same problem persists when using radiography, as the film cannot accurately illustrate the transition portion of the weld due to the slope of the bevel. This was a continual problem on most pipelines laid in the United Kingdom.

The other method occasionally applied in the U.S. is to use the American Petroleum Institute approved counter bore (see figure 1-2). This technique requires the wall thickness of the transition pipe to be reduced to the wall thickness of the lighter wall pipe used in the main line. The transition pipe is counter bored back approximately 2.5" to 3.0" and terminates with a 1:1.75 or 60 degrees slope until it meets the original wall thickness. This procedure will facilitate the effective use of non-destructive testing but creates other issues. The acute angle at the counter bore termination creates an area of stress at the point where the slope begins. Additionally, the use of this procedure can interfere with the flow of product and damage costly "smart pigs" used during the pipeline inspection.

Our solution to this problem is the new "Dyna Torque Bevel" which is a counter bore/transition combination bevel (see figure 1-3). When this bevel was introduced to British Gas/Transco, it was immediately tested, accepted, and ultimately written into their specifications for welding procedures. It is currently being used throughout Great Britain and Wales and, according to engineers and inspectors, it is making a significant difference in the interpretation of non-destructive testing.

The advantage of the "Dyna Torque Bevel" is its unique configuration in which the total weld is performed within the counter bore area (same wall thickness) as opposed to a transition area (increasing wall thickness) thus facilitating accurate interpretation of all types of non-destructive testing. Objective conclusions regarding weld quality are now being achieved.

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