Toyo Engineering Demands the Best FCC Expansion Joint

Technology for Kyushu Oil Refinery Ltd.

When Toyo Engineering was requested to supply replacement expansion joints for a Kyushu Oil Ltd. FCC, It was clear to everyone that the very best technology would be necessary. The customer had experienced cracking problems on certain high temperature FCC expansion joints and was very sensitive about the life span of expansion joints in FCC service. Senior Flexonics Pathway employed the most current technology available to insure the best performance for Kyushu Oil Ltd.

The double gimbal expansion FCC flue gas expansion joint was designed to handle 57 PSIG (4.01 Kg/cm2) at a temperature of 14270F (775 C). The expansion joint was of hot shell design. In order to eliminate problems with cracking of the pipe in service, the pressure thrust restraint rings attached to the hinge arms were designed to be floating structures. This floating ring concept allows the pipe to grow radially without being restricted by the cooler rings. In the creep range of operating temperatures, this feature is critical to avoid excessive pipe stress.

Stainless steel is subject to embrittlement after many years of service in the creep range. This problem is minimized by careful control of the ferrites in the deposited metal of pipe welds and by eliminating welds wherever possible. To minimize welds, Senior Flexonics Pathway used proprietary pipe expander equipment to create the four transitions required for the double gimbal design. This process eliminated 8 circumferential welds that otherwise would be required. Senior Flexonics Pathway also controlled the ferrite level of the weld wire and then solution annealed the pipe to put the pipe into the most satisfactory condition for long term use at high temperature.

Most Senior Flexonics Pathway customers consider a high nickel alloy like Alloy 625 to be the best expansion joint material for FCC service. However, FCC operating conditions are above the safe operating temperature for most high nickel alloys including Alloy 625. To keep the bellows in the best operating temperature range, Senior Flexonics Pathway internally insulated the bellows. A special type of high nickel alloy called Alloy 625 LCF was used for the bellows. Alloy 625 LCF is marketed exclusively by INCO Alloys. This very fine grain version of Alloy 625 has superior fatigue performance and resistance to embrittlement up to 1200OF (648 C), significantly higher than straight grade Alloy 625. To insure the very best fatigue performance, the bellows were not annealed after forming.

Each bellows was of ply testable construction. This concept involves a two ply bellows in which each ply is designed for the full operating conditions. This results in a 100% safety factor on the bellows elements and the ability to safely operate the expansion joint even if a leak occurs on the inner ply of the bellows. A Senior Flexonics Pathway patented Red Top leak detector system was installed on the ply testable pressure tap on the outer ply. The Red Top leak detector system has a highly visible red post that pops up if any leakage is detected in the inner ply of the bellows element.

With insulation inside the bellows, it is possible to have the bellows drop below the condensation point of acids in the media in severe weather conditions. To stabilize the bellows operating temperature and maintain a high enough temperature to avoid condensation that could corrode the bellows, external insulation was factory installed on the outside of the bellows elements.

Senior Flexonics Pathway also installed thermocouples on each bellows in the double gimbal to provide a method of monitoring the bellows skin temperature in service. The ideal temperature range is between 400OF (204OC) and 1000OF (538OC). By monitoring the bellows in service with thermocouples, operators can document that the bellows are operating in a temperature range that will result in the best long term performance of the expansion joint.

To find out more about expansion joints for FCC service, contact Senior Flexonics Pathway.