Asset Life Extension: How to Prove Ageing Plant Can Run Safely
The board meeting is in six weeks. The gas plant on the agenda reached its design life two years ago, the replacement option has…
The board meeting is in six weeks. The gas plant on the agenda reached its design life two years ago, the replacement option has been costed and deferred, and the integrity manager has been asked a single question: how much longer can it safely run, and what will it cost to get there?
That question is now routine across oil, gas and process plant. Platforms installed for twenty years are approaching forty. Gas plants, fertiliser units and tank farms built for one design life are being asked for a second, often on heavier, sourer or more variable feed than they were designed for. Answered well, life extension is the most efficient money an operator spends: it goes to the components the evidence condemns, not to the whole unit. Answered badly, it is either an expensive blanket replacement programme or an optimistic extension nobody can defend when an auditor, verifier or board asks for the basis.
One asset decision, thousands of component decisions
An asset does not reach the end of its life all at once. A forty-year-old platform may carry topsides piping in excellent condition, a separator with significant internal metal loss, a flare system that has been replaced twice and a jacket whose fatigue life is the real limiting factor. A thirty-year-old ammonia or urea unit may be sound in most of its carbon-steel service and life-limited in a handful of high-temperature or stress-corrosion-prone items.
A credible life-extension case is therefore built bottom-up, from the component register. Each item needs its own answer, and the asset-level decision is the sum of them.
What the case has to show
That current condition is known, not assumed. Life extension stands on inspection history. Where that history was gathered on a calendar and never graded, it needs auditing first — the subject of our earlier piece on rebuilding the inspection evidence an ageing asset never collected.
That the damage mechanisms are the ones operating today. The original screen was done for new equipment on design feed. Re-screen against API RP 571 for the service as it is now, and for the mechanisms that only appear with age: fatigue in cyclic and vibrating service, creep and embrittlement in high-temperature equipment, and corrosion under insulation as coatings and cladding reach the end of their own lives. If the plant has been uprated or its feed has changed, the inspection basis has probably moved with it.
That remaining life has been calculated, component by component. For vessels and piping, API 510 and API 570 derive remaining life from measured thickness, the minimum required thickness and a credible corrosion rate. For atmospheric storage tanks, API 653 and EEMUA 159 set the equivalent basis for shells and floors. Where a component is already below its minimum thickness or carries a flaw, API 579-1 / ASME FFS-1 provides the fitness-for-service route to decide whether it can keep running, at what conditions and until when. For fixed offshore structures, API RP 2SIM sets out the structural assessment that sits alongside the process-equipment case.
What cannot be inspected, and how that risk is carried. Every ageing asset has items with thin or no history: buried and sleeved sections, cold service under insulation, internals that are rarely opened. The case should name them and say how each is managed — targeted inspection at the next opportunity, conservative operating limits, or planned replacement.
Run, repair, replace: where the efficiency comes from
Once each component has an evidence-based remaining life, the register sorts itself. Most items run, with inspection intervals set by risk rather than the calendar. Some need repair or re-rating within a defined window. A few need replacement before the extension period begins.
This is where life extension pays for itself. Repairs and replacements are planned into scheduled shutdowns rather than discovered as unplanned outages. Inspection effort is concentrated on the life-limiting items instead of spread evenly across equipment with decades of margin. And capital requests go to the board with the evidence attached, rather than as a contingency.
Conditions that shorten the clock
Remaining life is not a fixed number; it is a rate, and operating conditions change the rate. High humidity, high ambient temperature and chloride-laden coastal air accelerate external corrosion and CUI. Seasonal weather can shrink the access window for an offshore or coastal inspection campaign to a few months a year, so a deferred inspection may slip a full season. Heavier or sourer feed brings wet H₂S and high-temperature sulphidation into circuits that never saw them. A life-extension case built in these conditions has to be reviewed more often, and every new inspection result should be able to change it.
Make it a living case, not a report
The weakest life-extension cases are documents: commissioned once, approved once and filed. The strongest are living records that integrity, maintenance, verification and risk teams all work from — updated each time an inspection is closed, an anomaly is raised or a repair is completed, and reportable to management and to the board at any point. When the case and the day-to-day integrity data live in the same place, the question “is this asset still fit to run?” has a current answer, not one from the last study.
Where ONE fits
ONE was developed with operators extending the life of ageing North Sea assets, and the discipline transfers to any production, process or storage estate. The Component Asset Register holds each component with its design, material and inspection history. From repeat inspection-point data, ONE calculates corrosion rates and remnant life and trends them over time, as we described in our recent piece on trustworthy AI in asset integrity. Risk Based Assessment sets intervals on your own risk scales, Anomaly / Defect Management tracks every repair and fitness-for-service decision to close-out, and Reporting and KPIs gives management and the board a current view of the case.
Facing your own “how much longer?” question? Talk to us about what the run, repair and replace picture for one of your ageing assets would look like in ONE.