Basis of Estimate — Maintenance Turnarounds
A turnaround estimate is unlike a new-build: its scope is a worklist, its biggest risk is discovery work, and its cost is welded to duration because every shutdown day is lost production. The turnaround BOE must pin down all three — what's in the worklist, how much discovery is allowed, and the schedule basis behind the number. Built on AACE 116R-21.
What this standard adds
This is the BOE companion to the turnaround classification (Lesson 12) — and the third BOE industry variant, after process (Lesson 18) and software (Lesson 19). The general BOE backbone holds; what changes is which entries make or break the number. For turnarounds, those are the worklist, the discovery allowance, and the schedule.
What's distinctive in a turnaround BOE
- Worklist basis & freeze status — The worklist version the estimate reflects, and whether scope is frozen — the single most important entry.
- Discovery allowance basis — How much found work is allowed for, and the historical/inspection data behind that figure.
- Duration & schedule basis — The assumed shutdown duration — since cost (and lost production) hinge on it.
- Resource & execution basis — Crew sizes, shifts, contractor strategy, and peak manpower assumptions.
What to document in a turnaround BOE
| Element | Turnaround emphasis |
|---|---|
| Worklist basis | Version, freeze status, inclusions/exclusions |
| Discovery allowance | The found-work provision and its data basis |
| Duration / schedule | Assumed shutdown length and critical path basis |
| Resourcing | Crews, shifts, peak manpower, contractor strategy |
| Rates & productivity | Labour rates and turnaround productivity assumptions |
| Lost-production basis | How downtime cost is treated (if in scope) |
| Allowances & contingency | Beyond discovery — weather, access, late additions |
Using the turnaround BOE well
For a turnaround estimate, lead the BOE with the worklist basis and freeze status, state the discovery allowance and its data source clearly, and document the assumed duration and resourcing the cost depends on. Tie it to the turnaround classification (Lesson 12) so the class, worklist maturity, and BOE all tell a consistent story — and so a normal level of found work is understood as planned-for, not as failure.
Nine things to remember
- 116R-21 tailors the general BOE to turnarounds — worklist, discovery, duration.
- The worklist basis is the scope statement — the turnaround's "battery limits".
- Document worklist version and freeze status — the single most important entry.
- State the discovery allowance and that it's an allowance — beyond it is real risk.
- Document the duration basis — cost and lost production hinge on it.
- Record resourcing — crews, shifts, peak manpower, contractor strategy.
- Tie the BOE to the turnaround class (Lesson 12) for a consistent story.
- Same backbone, turnaround anchors — foreground the decisive entries.
- One BOE discipline, several dialects — general, process, software, turnarounds.
Glossary
- Basis of estimate
- The documentation of how the estimate was prepared.
- Discovery allowance
- Provision for found work, based on history.
- Duration basis
- The assumed shutdown length driving cost.
- Lost production
- Revenue forgone during downtime.
- Peak manpower
- The maximum workforce on site at once.
- Scope freeze
- The cut-off for adding planned work.
- Turnaround (TAR)
- A planned plant shutdown for maintenance.
- Worklist basis
- The worklist version and status the estimate reflects.