Not everything improves with age. Control system performance generally degrades over time. As systems near obsolescence, control strategies fail to take account of changes in the plant, resulting in declining operating performance, reduced reliability, rising maintenance cost, and difficulty in sourcing affordable spares. Eventually, experienced personnel with systems knowledge begin to retire.
In fact, the cost of the distributed control system (DCS) is relatively trivial in comparison to the outsized impact it has on plant performance and the cost of lost production from unplanned downtime. Yet the number of control systems in operation that are two or three decades old shows that many manufacturers delay migration as long as possible. In most cases, the rising costs of obsolescence alone are not enough to prompt the change. Instead, some other factor forces the upgrade: compliance requirements or changing demand conditions that cannot be met due to system constraints; or mergers and acquisitions that bring the desire to standardise on a single control solution.
One reason for this delay is the cost, although this is usually a false economy, given the price associated with a control system failure. A more defensible reason is the potential for disruption to the operation. At worst, a poorly planned migration could bring about the key risk of downtime that it is designed to prevent. As a result, many plants are willing to bear the escalating costs of obsolescence until forced to migrate by an external influence.
Risk and reward
This reluctance to migrate may be understandable, but it is ultimately misplaced. First, and most obviously, it does not address the obsolescence itself; it merely postpones the point at which it must be confronted. Worse, the risk of downtime will grow in the meantime. If plants are balancing the danger of a control system failure resulting from obsolescence against disruption to the operation from migration, they should recognise that the balance is constantly changing – and in favour of the latter.
Moreover, by tackling the issue early, plants give themselves time to make better migration decisions. Waiting for changes in regulatory requirements or withdrawal of system support ensures decisions will be made under pressure. It may also mean delays in the ability of plants to respond to changes. Plants waiting to migrate until greater flexibility is required, for example, face perhaps an 18-month delay for evaluation, engineering and delivery before they can meet the challenges posed by changing market conditions or customer demand.
Indeed, this relates to the final point: by postponing the costs of migration (since it cannot be eliminated), plants also postpone the benefits. There is certainly a cost to migration, but also an opportunity cost in delay.
It is this positive case for migration that perhaps most strongly argues for addressing obsolescence early. Even ignoring the costs of obsolescence and growing risk of downtime, the payback period for a migration of the control system can be relatively rapid (perhaps as little as 10 years for a batch plant, through automation and optimisation).
In simply focusing on the costs of obsolescence and migration, plants risk missing out half the equation. Evaluating only the costs – as opposed to potential benefits from migration – they are also considering only the short-term factors for what is a long-term decision. They are likely, for instance, to stick with the existing control system vendor for the migration as the route to minimise the short-term risks of disruption to the process. This fails to address whether such an approach maximises the benefits to the operation over the long-term, however…
Written by Satnam Bhogal, Honeywell Process Solutions, UK.
This article was originally published in the June 2020 issue of Hydrocarbon Engineering. To read the full article, and other great technical articles in this issue, view the full issue here. You can also register to receive a free regular copy of the magazine here.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/09062020/migration-picking-the-right-moment/