Senior Flexonics Pathway Builds Improved Design

MTBE Expansion Joints for Super Octanos

The lines connecting the reactors on the ABB Lummus Crest Catofin unit used in MTBE production operate at 12000 to 13000 F. These lines vary from 18" to 84" diameter and are externally insulated, insuring that the pipe wall operates at close to the media temperature. The close proximity of the reactors and the large line sizes requires the use of dozens of expansion joints on a typical Catofin unit to handle thermal growth of the piping and reactors. Vibrations caused by changing process conditions in the lines add intensity to the harsh operating environment.

The expansion joints at the Super Octanos MTBE facility in Venezuela were built by a respected European manufacturer u sing conventional hot wall design principles. The expansion joints had single ply reinforced bellows designed to operate at the media temperature. This meant that the bellows would be operating at temperatures where creep strength was the limitation on design.

After experiencing several bellows failures, the Super Octanos facility purchased an upgraded design for 2-36" slotted hinged expansion joints, 1-36" gimbal and 2-18" gimbal expansion joints. The detail design specification was provided by Refinery Technology, Inc., a Houston based engineering consultant that was hired by Super Octanos to review the piping design of the Catofin unit. The final design approved by RTI included many features that have been promoted by Senior Flexonics Pathwayfor high temperature expansion joints in recent years.

The replacement expansion joints were designed with internally insulated bellows to insure that the bellows would operate below 8000 F There is little information on fatigue characteristics of bellows operating in the creep range (above 8000 F). Keeping the bellows operating temperature below 8000 F insured that the bellows would have a cycle life that could be accurately predicted by industry design standards.

The bellows were two ply testable construction so that a failure of the inner ply could be recognized and monitored without causing an emergency. Because the bellows were designed to operate at a temperature where the bellows material strength was limited by ultimate tensile strength instead of creep strength, the bellows did not require any external reinforcement. Without reinforcing rings the entire exterior of the bellows were available for future field inspections and the bellows were less complicated to manufacture.

On the new hinge and gimbal expansion joints, the restraint hardware transferring pressure thrust forces from the hinges to the pipe shell were constructed with a floating ring design. Conventional design would incorporate the use of a fixed ring or fixed double rings welded directly to the pipe shell. Fixed ring design on high temperature applications causes a very high stress in the pipe shell that can result in cracking of the pipe shell over long periods of operation. The floating ring design eliminates this possible failure mode. Based upon the very favorable experience Senior Flexonics Pathwayhas had with the above design features on FCC power recovery systems and other high temperature services, these replacement expansion joints should last the life of the Catofin unit.

To inquire about expansion joints for MTBE service or other critical applications, contact Senior Flexonics Pathway, 2400 Longhorn Industrial Drive, New Braunfels, Texas 78130.