Turnaround Inspection Planning for Ageing Plant: Stop Scope Growth

Most turnaround inspection workscopes get built twice. First on paper, months ahead, from whatever list was used last time. Then again on the day the column is opened and the scaffold is up, when inspectors find what the paper scope did not expect and the shutdown clock is already running.

On an ageing oil, gas or process plant that second build is expensive, and it is the most common failure in turnaround inspection planning. The turnaround is often the only chance in four, five or six years to see inside most of the pressure equipment, and the window is fixed by production commitments and, in many places, by the weather. Every item opened without a reason costs days and money. Every item that should have been opened and was not waits a full cycle. The inspection workscope is where that trade-off is won or lost, and it is better treated as a controlled, evidence-based list than as a tradition.

Here is how that list is built and held, milestone by milestone.

Twelve months out: build the candidate list from evidence, not habit

Start with three inputs, not last turnaround’s scope.

Risk ranking. A current risk-based assessment, in line with API RP 580 and API 581, says which items have the highest probability and consequence of failure and which inspections are actually due on risk. That is the backbone of the scope. Items that are only on the list because “we always open it” should have to earn their place.

Open anomalies and temporary repairs. Clamps, sleeves, deferred repairs and conditions found by on-stream inspection that can only be closed with the unit down. If they are not pulled into the scope deliberately, they roll over to the next cycle.

A damage-mechanism review for the service as it now runs. Feed, throughput and operating envelopes drift over a plant’s life. A crude and vacuum unit now running heavier or higher-sulphur crude, a gas plant whose sour content has crept up, or an ammonia and urea plant whose synthesis loop has seen decades of thermal cycling may each have active mechanisms that the original inspection plan never targeted. Re-check them against API RP 571 so the scope picks the right method as well as the right item. If the plant has been uprated, the inspection basis has probably moved too.

The output is a candidate list where every line has a reason attached: the risk driver, the anomaly number or the mechanism. On ageing plant, check the quality of the records behind each reason as well, because an interval set on poor history is no basis for leaving an item closed. We covered how to grade inherited records in Before the Interval Lengthens.

Six to nine months out: freeze the scope, with the basis written down

A scope that is never frozen cannot be planned, resourced or priced. Scaffold, blinds, cranes, specialist inspection techniques and long-lead spares all depend on it. Freezing it means agreeing, across integrity, maintenance, operations and turnaround planning, that the list is fixed and that anything added after the freeze goes through a defined change route.

The freeze is only defensible if the reason for each item, and for each item left out, is recorded with it. Each item should then become an inspection task with a defined method, extent and acceptance criteria, following API 510 for vessels, API 570 for piping, API RP 572 for vessel inspection practice and API 653 where tankage is in the outage. Grouped by unit, discipline or access, those tasks become the inspection workpacks the contractors will execute.

During execution: when inspection finds more than expected

Scope growth is not a failure. Opening ageing equipment will find things, and finding them is the point. What matters is that each discovery is decided on evidence and at the right level, not by whoever is loudest at the morning meeting.

Every finding needs four answers, recorded where the next engineer will see them. What was found, measured and photographed? Is the item fit to return to service, with a fitness-for-service assessment under API 579-1 / ASME FFS-1 where it is below its required thickness or carries a flaw? Is the repair needed now, or can it be safely planned for a later window under interim measures? And does the same mechanism suggest that similar items elsewhere on the unit, which were not in scope, need to be added?

That last question is where scope growth should come from: a reasoned extension driven by a confirmed mechanism, not a general nervousness that adds days.

Before box-up: capture the record, not just the repair

The moment a vessel is closed, the opportunity to record its internal condition is gone for years. Before box-up, confirm that thickness readings are logged against their inspection points, that photographs and reports are linked to the component, and that every finding has an owner and a disposition. A finding left in a contractor’s spreadsheet is a finding that will be rediscovered, expensively, at the next turnaround.

After the turnaround: let the findings write the next plan

The final step is the one most often skipped. The findings should update corrosion rates, remaining life and the risk ranking straight away. Items that were in better condition than assumed earn longer intervals. Items that were worse move up. Mechanisms confirmed on one unit are checked on similar units. The next turnaround’s candidate list then starts from what was actually found, which is how inspection effort on an ageing plant gets smaller and better targeted over time, not larger.

Where ONE fits

ONE keeps the risk basis, the anomalies, the workpacks and the field results in one dataset, so the scope is evidence-based going in and the plan updates itself coming out. Risk Based Assessment produces inspection risk and frequency on your own matrices. Anomaly / Defect Management shows every open anomaly and temporary repair across assets in one window. Workpacks and Inspections builds workpacks from task templates, grouped by inspection type, equipment, discipline, location or campaign window, and tracks progress across assets. In the field, Mobile ONE records results against the component, including on intrinsically safe hardware, and new anomalies can be raised in the same workflow without re-keying. Risk assessments are superseded rather than overwritten, so each change in the basis keeps its history. Operators of mature assets, such as TAQA Bratani, use it to have work scope requirements available at the click of a button. More on how ONE supports oil and gas asset integrity management.

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Frequently Asked Questions

Thickness readings and findings from the turnaround should update corrosion rates, remaining life and the risk ranking as soon as they are recorded. Equipment found in better condition than assumed can justify longer intervals, while worse condition moves items up the next scope, so each turnaround’s scope is based on what was actually found.