Hydraulic Expansion Process
Dura-Bond Pipe utilizes a unique hydraulic expansion process. Some mills utilize a mechanical expander and most do not have any expander. With our process, the pipe is pressurized with water until the steel begins to yield. The pipe is then forced against a steel die to its final shape and diameter. A common expansion ratio is 1.25%. This process accomplishes a number of important items. First, in ensures even dimensions throughout the body. This is especially important when making field cuts and fitting up cut ends in the field. Second, the over-pressurization (up to 5000psi) will expose any weakness in the product prior to Phased Array UT and End X-Ray of the long seam weld and body. Third, the expansion and subsequent hydro-test (always performed at 100% SMYS) is completed on the same machine which reduces mill cycle times. Most importantly, since the pressure is known at the point where the pipe starts to yield, we are able to determine if the yield strength of each joint of pipe meets the specification that it is being produced to. This is in contrast to all other mills that only test one pipe out of each heat in most cases. There have been many reported cases of pipe installed from other manufacturer’s that expanded in field hydro tests or while in service and found to be below the minimum specified yield. This has never been an issue with Dura-Bond’s expanded pipe.