Discussion of controllers in the continuous process industries typically centers on distributed control systems (DCSs). However, programmable logic controllers (PLCs) play as important a role in the process industries as they do in discrete manufacturing, particularly when it comes to operations reliability and protection of personnel. Some of the more significant applications for PLCs in the process industries include control of safety-instrumented systems and control of major machinery.
Like many discrete manufacturing operations, most process operations use a variety of PLCs from different vendors. As a result, your ability to effectively operate and manage these disparate PLC versions has a direct impact on your plant reliability and safety.
Following is a list of the top three PLC lifecycle management concerns for the process industries and how some of your peers are working with PLC suppliers to address those issues, compiled from presentations delivered at The Automation Conference 2012.
1. Long plant maintenance shutdown intervals limit the opportunity to modify, maintain and upgrade PLCs. Many process industry units, particularly in continuous process operations, run eight years or more without shutting down. As a result, your opportunity to do anything with the PLCs in that unit is very limited. Therefore you need to ensure that PLC management is a key part of your unit maintenance focus.
2. Standardization of PLCs is difficult, if not impossible in a multi-plant operation, and leads to challenges with spare parts management and training. Because across-the-board standardization is unlikely due to regional differences tied to support and availability, a strategy for PLC support and training for each region should be developed to ensure that these critical controllers are maintained in a standardized fashion.
3. Integration with main control systems — Three aspects are critical to any plan involving the integration of PLCs with DCSs. 1) The integration process needs to be reliable and shareable with all other plants to standardize the process for ease of maintenance; 2) the integration plan should be flexible for adaptability to local requirements; and 3) it must address industrial control system security.
To better manage your PLC lifecycle, following is a set of three requests that many top process industry operations are asking of their PLC vendors to help them better manage their PLC assets over the long, continuous operation periods common to the process industries.
1. Life extension. Because of the long periods of time that typically pass between maintenance shutdowns in process facilities, users need to be able to source and use components for longer-than-expected lives. Many facilities in the continuous process industries are still looking at 20 to 30 years as a life cycle for their equipment. Talk to your vendor about their ability to support backwards compatibility with new components as they become available over these long lifecycles. These new components should be able to be integrated into your system without requiring a shutdown for upgrading.
2. Online upgrades. More vendors are coming around to this request of process industry end users, as it is often the easiest way to upgrade a PLC’s logic without shutting it down or rewiring the I/O. One process industry end user told us: If you look at the total cost of an upgrade, the cost of the hardware is dwarfed by the cost of labor to re-do things like I/O rewiring and the cost of the unit shutdown. Therefore, online version upgrades that can be installed while the PLC is running and that work with the existing I/O is ideal.
3. Increased flexibility in design to address standardization.
More end users in the process industries are looking for scalable PLC systems from vendors that use the same hardware. Having the same hardware requirements across-the-board for your PLCs enables you to better manage spare components, training, and configurable I/O requirements.
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