Emerson Exchange 365

As part of the early planning Front End Loading (FEL) 1 or 2 processes for modernizing your legacy process control system, the question of how to switch or cutover from the legacy system to the new replacement system is asked. The choices considered are:

1. Cold cutover
2. Hot cutover

A cold cutover is switching over from the legacy control system to the new control system while the process is not running, or “cold”. This is usually occurs during periodic outage/shutdown/turnaround depending on the terminology used by the customer.

A hot cutover on the other hand, occurs as the name suggests, while the plant is in operation or “hot”. The new system is cutover point by point, loop by loop. This cutover methodology requires meticulous planning and orchestration but brings considerable benefits as we will as this discussion develops.

What cutover strategy is “best”? I would suggest the question is which strategy is the right one for your process/project. Regardless, both need to be considered as part of the early planning process to define and discern the “right one” for you.

Here are my thoughts on cutovers …

1. Cold Cutover

• Many consider this the default low risk option from the tripping the plant perspective, you can’t trip  a plant and create a hazardous situation if the process is not running, no loss of production
• It is easier to execute from an engineering and installation perspective, install the system, test and loop check it and turn it on
• There is greater flexibility in manpower/resources deployment, if space and time allows
• Plant shutdown time windows have a direct effect on cold cutovers, as meticulous and detailed planning needs to happen before the plant comes down; field IO and devices need to be consolidated and defined as any undiscovered IO will lead to system cutover and start up delays which leads to, yes, production loss
• Unless an effectual training program was conducted prior to cutover, and start-up, operators will need to learn the new system “cold”

2. Hot Cutover

• Thought to be “risky and dangerous” 
• May be only option for processes that cannot be shut down in time or long enough to effect a cold cutover e.g. oil refineries
• Needs meticulous planning and orchestration of resources, and typically requires more time to perform
• Done right, no production loss will occur as process is running and the new process control system is cut in loop by loop
• Operationally, process issues – trips, upsets – are eliminated allowing for smoother transition
• Operators can be eased into the new system even if prior operations training was provide
• Maintenance personnel can also be familiarized with the system as it is cutover instead of a one-shot event as a cold cutover would be
• For some continuous processes, a shut-down/start-up cycle brings many hazards and starting up with a new control system can be very risky , a hot cutover can mitigate and even eliminate that risk

These are my thoughts, what are yours? Please feel free to share them with EE365 Community.

For further reading, here are some past Emerson Process Experts posts on cutovers.

http://www.emersonprocessxperts.com/2008/07/automation_syst/

http://www.emersonprocessxperts.com/2008/08/more_thoughts_o/ 

Come discuss cutovers with us, the Emerson Systems Modernization Team at 2016 Emerson Global Users Exchange in Austin, Texas October 24 to 27.