Control System Obsolescence
HOW TO MAXIMIZE THE LIFE CYCLE OF CONTROL SYSTEMS USED IN TURBOMACHINERY
Figure 1: The Bathtub Curve (Hypothetical Failure Rate vs. Time)
Plants have different operating philosophies when it comes to the lifecycle of the system in charge of controlling and protecting turbomachinery. In most cases, these operating philosophies can be summarized into three distinct strategies: Run till it breaks, preventive maintenance, and scheduled upgrades or retrofits.
Others may adopt a combination of strategies when facing the common issues related to electronic component obsolescence. Ultimately, each strategy has pros and cons. It is a matter of finding a balance between managing risk, cost and maximizing productivity.
The “run till it breaks” approach basically addresses maintenance and other lifecycle concerns on a run-to-failure basis. Maintenance costs are minimized at the expense of higher long-term costs. Having outdated or obsolete control systems running critical turbomachinery can be dangerous for the personnel involved in the operation.
Poorly serviced systems could present a problem from an operational point of view; changes in another connected system or in field equipment and instrumentation can be overlooked, compromising the correct functionality of the system. Similarly, lack of training in a plant operating under a run-tofailure approach can create problems during an emergency. Further, this approach can lead to downtime and production delays.
Planned maintenance
A preventive maintenance program at a minimum should be comprised of periodic inspection and testing, planned maintenance actions, and a plan to assess and fix anything further that comes up. This approach makes it possible to reduce the number of electronic spares kept in inventory. It is also found to be more cost effective than performing emergency repairs, and can sometimes help in obtaining a reduction in insurance premium.
But preventive maintenance is not risk free. Anytime someone is performing tests and working on electronic equipment, a certain component of risk involving human error must be accounted for. For this reason, many plants prefer to align preventive maintenance, when possible, with scheduled outages. Replacing electronic components during outages represents an obvious long-term benefit for system lifecycle. But plants should be aware of what is known as the “infant mortality” period depicted by the Bathtub Curve (Figure 1).
But sooner or later, every company has to face the inevitable end of life of aging technology. New electronic spare components become expensive and hard to find. Even vendor repaired and refurbished parts become difficult to obtain.
At that stage, a control system upgrade or retrofit is the only solution. Whether to upgrade or retrofit a new control system is a big decision. Factors to take into account include: Has the system been modified and improved over the span of multiple years? By retrofitting the system to a different vendor is it possible to guarantee a “like for like” or is there risk of losing functionality? And as the system is interconnected with many other systems from multiple vendors, who is ultimately taking responsibility for the overall project?
When dealing with controls for multiple turbomachinery trains, it is best to develop a long-term lifecycle plan. Some plants plan as far ahead as ten years for a system upgrade and retrofit. A large end user, for example, recently disclosed plans for the control system upgrade of six turbomachinery trains that are always in operation with outages planned only once every seven to ten years. The upgrade, installation and commissioning of the first train is scheduled for 2017 and the last one for 2024. Upgrading one train at a time over the span of a long period allows for better planning and focusing of resources.
Some vendors offer programs to maximize the benefit of this approach. This might include hardware buyback programs and refurbishing of used electronic components: This way the user can obtain savings on the upgrade or have decommissioned hardware sent back to the manufacturer for refurbishing. Reconditioning the old hardware is a good way of stacking up on more electronic spare components for the remaining trains still operating with older technology.
For plants that do not have an effective process for keeping an inventory of electronic spare components, it may be wise to look for vendors that offer spare parts management. Such a plan may also work for plants that have settled for a run-to-failure strategy.
Having the vendor manage spares in addition to a 24-hour service agreement can make the difference in the event of emergency hardware failure, relieving the user from having to obtain a PO and shipping material on site. For those using preventive maintenance, service agreements that comprise remote diagnostics are a good way of minimizing the cost of routine maintenance checks by eliminating travel expenses.
