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Can double disc isolation valve technology shorten fluid catalytic cracking unit turnarounds?
Written By Elke Baum
April 21, 2026
Double disc isolation valve technology may help improve the safety and efficiency of maintenance activities during fluid catalytic cracking unit (FCCU) turnarounds in refineries.
This article explores key operational challenges and how improved isolation strategies can support safer shutdown and startup procedures.
Safety considerations in Fluid Catalytic Cracking Unit (FCCU) operations
A fluid catalytic cracking unit (FCCU) is a core processing system in many refineries, but it involves high temperatures and hydrocarbon-rich environments that require strict operational control during maintenance.
On 18 February 2015, an incident occurred at a refinery in California involving an electrostatic precipitator (ESP), a pollution control device used on the air side of an FCCU. During normal operation, the ESP removes catalyst particles using electrically charged plates that can generate sparks.
During an isolation attempt for maintenance, hydrocarbons backflowed through the process. The resulting ignition of flammable material led to an explosion, injuring two workers and releasing debris beyond the site boundary.
While the injuries were not life-threatening, the event highlighted the importance of robust isolation procedures during FCCU shutdowns and maintenance activities.
FCCU isolation challenges and turnaround complexity
FCCU shutdown and startup operations require the reactor to be safely isolated from the main fractionation system. This is typically achieved through manual intervention, including:
Removing a spacer ring (typically 24–100 inches)
Installing a plate blind to achieve isolation
Exposing personnel to high-temperature hydrocarbon streams during the process
At the reactor overhead vapour inlet to the main column, conditions can exceed 300°F (approximately 150°C). During certain maintenance stages, temperatures may reach up to 600°F (approximately 315°C), particularly during startup and refractory dry-out.
Fluid catalytic cracking unit where effective reactor isolation plays a critical role in improving safety and efficiency during shutdowns and turnarounds.
These conditions mean that even brief exposure can pose significant safety risks, including the potential for flash fires if hydrocarbons and oxygen are present together.
In addition, the full isolation and blinding process can extend turnaround activities by up to 36 hours, making it part of the critical path for FCCU shutdown and restart operations.
Improving isolation in Fluid Catalytic Cracking Unit (FCCU) turnarounds
One approach to improving both safety and efficiency is the use of automated isolation solutions positioned between the FCCU reactor and the main fractionation line.
A double disc isolation valve can enable rapid isolation of the reactor during planned or unplanned shutdowns without releasing hydrocarbons into the atmosphere. This helps reduce operator exposure during blinding operations and supports more controlled maintenance conditions.
When integrated into FCCU systems, valve actuation can also enable parallel workstreams. For example:
Catalyst removal and main column washing can proceed concurrently when isolation is secured
Certain mechanical activities, such as bolt retorquing, can continue while systems are being brought up to temperature
Compared with traditional sequential blinding methods, this approach can reduce downtime associated with isolation activities.
Double-disc through conduit gate valve design for severe service
Double-disc through conduit (DDTC) gate valves are designed for demanding on/off isolation applications such as FCCU service.
Double disc through conduit isolation valve engineered to provide reliable shut‑off in high‑temperature FCCU reactor overhead applications.
Their design includes:
Two independent shut-off discs for improved isolation integrity
A split-wedge-ball mechanism that supports controlled disc movement
Non-self-locking wedges to help prevent jamming under high or variable temperatures
This configuration supports double block and purge capability, helping ensure effective isolation during maintenance activities.
For FCCU applications, this is particularly relevant when reliable isolation is required under high-temperature, coking conditions.
Enhancing durability in FCCU operating environments
FCCU reactor overhead vapour lines operate under severe service conditions, including high temperatures, corrosive media, and catalyst-laden flows. Equipment used in these environments must therefore be designed for wear resistance and long-term reliability.
Double-disc through conduit gate valves used in such applications are typically engineered with:
Wear- and corrosion-resistant seat overlays
Seat geometries designed to reduce process-related wear in both open and closed positions
Design features that minimise seat-to-seat friction and mechanical stress
Consideration of external piping loads to reduce seat deflection effects
These characteristics support consistent operation during repeated FCCU cycles, where reliable isolation is essential for both safety and operational continuity.
Conclusion
FCCU turnaround activities require complex isolation procedures that place maintenance teams in challenging and potentially hazardous conditions. Manual methods such as spacer removal and blind installation can extend shutdown durations and increase exposure to high-temperature hydrocarbon environments.
Double disc isolation valve technology offers an alternative approach that can support faster, more controlled isolation while improving operational safety. When applied within FCCU systems, these valves can help reduce turnaround complexity and support more efficient maintenance planning.
Learn more about our double-disc through conduit (DDTC) gate valves and our other IMI Z&J isolation valves.
A version of this article originally appeared in the July 2025 edition of Hydrocarbon Engineering magazine.
