Expansion joints used in FCC units service are highly engineered units and one of the most critical and complex types of expansion joints manufactured. These expansion joints are exposed to high temperatures, high pressures, large movement conditions, and very aggressive media.
We design and manufacture FCCU Expansion Joints according to UOP, ExxonMobil, KBR, Lummus, etc. specifications.
Our technicians are experienced, knowledgeable engineers who have worked throughout the world in innumerable refineries.
Typical types of expansion joints used in FCCU applications are: Restrained Universal, Gimbal, Hinged and Pressure Balanced (in-line and elbow type) and are categorized in three major groups:
The Hot Wall Units incorporate an abrasion resistant lining, including hex-mesh and castable material or refractory (a multi-purpose abrasion resistant castable which can be hand-packed, vibration cast and gunned). The lining is not intended to be used as a thermal barrier and requires a specific and controlled drying.
The Cold Wall Units are refractory lined to ensure the shell wall temperature does not exceed the allowed parameters. The lining consists of stainless steel anchors and a high-density vibrocast/ self-levelled refractory material.
They incorporate internal insulation/packing made of bio-soluble ceramic fibre or silica blankets, a liner seal that keeps in place the internal insulation blankets while keeping fluid particles out of the bellows/liner cavity.
The Unlined FCC Unit Expansion Joints can be exposed to very high temperatures but usually do not convey catalyst so they do not require abrasion resistant lining. This type is generally used for inlet and outlet air and transferring gases from the reactor.
The bellows, as the most critical part of the Expansion Joint, can be single ply, multiply, redundant ply or reinforced and generally incorporate an early warning system (active or passive monitoring). FCCU expansion joints generally incorporate 2-ply testable bellows where each ply is designed for the full operating conditions. If a hole or stress crack develops in the inner ply during service, the outer ply takes over without exposing operators to increased risk or creating the need for an unscheduled shutdown.
The annular space between plies can be monitored for leakage to detect a ply failure. This will serve as a warning of an imminent problem. A pressure device in the outer ply alerts about the inner ply failure. The 2-ply testable bellows also allows inspectors to pressure test the inner and outer ply during shutdowns. There are several types of devices used for monitoring the 2 ply testable bellows from simple pressure gauges to electronic devices and can be categorized as Active and Passive Monitors.
Passive monitor: when the inner ply fails the monitor is activated by the pressure between the plies.
Active monitor: the active monitor can detect inner and outer ply failures. A vacuum is created between the inner and outer ply before installing the monitoring device. If the inner ply fails, the pressure between the plies will activate the monitoring device and if the outer ply fails the vacuum will be lost and the monitoring device will be activated.
The material for bellows for most FCCU applications is Inconel 625LCF. INCONEL® alloy 625LCF (UNS N06626 / W. Nr. 2.4856) developed as a fatigue-resistant, bellows- quality version of INCONEL alloy 625. Most specifications require for the bellows to be annealed, or solution annealed, after forming.
To avoid the dust entering into the bellows cavity as the catalyst can solidify and damage the bellows or restrain the movement capability packed or purged bellows are used. The most frequent is the packed bellows. Purged bellows are not as commonly used today.
Self-equalizing rings are commonly used on FCCU Expansion Joints to prevent the convolutions from contacting each other ensuring a uniform compression distribution over the convolutions.
FCCU joints usually fit in different types of external hardware. The most widely used are: Control Rods, Pantographic linkages, Slotted Hinges, Gimbal Pantographs, pressure retaining covers, aeration pipes, etc . and each type is used to execute precise and different functions on FCCU Expansion Joints.
All MACOGA FCCU Expansion Joints undergo a comprehensive quality control and testing programme including: Review Drawings, Review Calculations, Check Material and welding consumables Certificates, Review and update WPS, PQR and WQR, Review NDE Procedures & Operator Qualification, RT - Radiographic Examination, PT - Liquid Penetrant Examination, MT - Magnetic Particle Examination, Hardness Testing of Welds, Pressure & Leak Detection Test, PMI Positive Material Identification, Inspection of Refractory Lining, Surface Preparation & Paint System, Check Packing & Marking, etc. An exhaustive Inspection Plan is issued for every expansion joint for customer's review and approval.