Scope freeze.
A scope freeze is the point in a turnaround or project schedule after which no new work may be added to the agreed scope without passing through formal change control. It locks the worklist so planning, materials, and resource loading can proceed against a stable baseline.
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What Scope freeze means.
A turnaround lives or dies on its worklist. In the months before the event the scope is built up from inspection findings, deferred work, modifications, and statutory tasks, then frozen on a published date so that planning can convert it into a schedule, a materials order, and a labour plan. After the freeze, anything new has to be justified through a change board rather than slipped quietly onto the list, because every late addition competes for the same critical path and the same shutdown window. The frozen scope includes the instrument and valve worklist, the isolation list, and the tie-in list, all of which are planned against the register that was current at the freeze. A register that is accurate on the freeze date protects the estimate. One that is stale carries error straight into the plan.
Why a scope freeze exists
The freeze protects the critical path. Once the worklist is locked, planners can size labour, order long-lead materials, and sequence the work with confidence that the target is not moving. Without a freeze, late additions accumulate until the window can no longer absorb them and the turnaround overruns.
What gets frozen
The frozen scope is the full worklist. It holds inspection and maintenance tasks, modifications, the instrument and valve list, the isolation and lock-out list, and the tie-in list for any new connections. Each item is planned against the engineering records that are current at the freeze, so those records need to be reconciled before the date, not after.
Change control after the freeze
Work identified after the freeze is handled through a change board, which weighs each request against the critical path and the available resource. Emergent or discovery work found once equipment is opened is a recognised category with its own approval route, kept separate from scope that could have been planned earlier.
Scope freeze versus design freeze
A design freeze locks the engineering. Drawings and specifications stop changing so procurement and fabrication can proceed. A scope freeze locks the execution worklist for a turnaround or project phase. A project can hold a design freeze long before the scope freeze for the shutdown that installs the work.
The freeze gates on a project or turnaround, and what each one locks
Projects run several freezes at different moments. They are often all called the freeze in conversation, which is how work gets added after the wrong one.
| Freeze | When it falls | What it locks | What still moves | Route for a change after it |
|---|---|---|---|---|
| Design freeze | At the end of detailed engineering, before fabrication release | The design basis, the P&IDs, the equipment list and the layout | Vendor detail and field fit dimensions | A design change notice, authorised by engineering |
| Scope freeze | A set number of weeks before the execution window opens | The agreed worklist and the estimate built on it | Emergent work found once equipment is opened | The late addition process, authorised by the steering group |
| Material freeze | When long lead procurement has to commit | Bills of material and requisitions | Consumables and stock items | Procurement with engineering, and a schedule impact assessment |
| Schedule freeze | When the execution plan is issued to the field | The sequence, the durations and the resource plan | Day to day re-sequencing inside the window | The turnaround manager, at the daily plan review |
| Document freeze | Before drawings are issued for construction | The revision of each drawing handed to the field | Field queries answered by request for information and site instruction | Document control, through the management of change route |
What a late addition costs, by how late it arrives
The cost of adding work is not linear in time. Each column names the constraint that is no longer available, which is the reason for the freeze rather than a policy preference.
| Arrives | What is still available | What is already committed | Typical consequence |
|---|---|---|---|
| Before the scope freeze | Estimate, materials, labour and schedule can all absorb it | Nothing | Normal planning |
| After the scope freeze, before material commit | Labour and schedule can absorb it | The estimate and the approved budget | A budget variation and a re-estimate |
| After material commit | Schedule can absorb it if there is float | Estimate, budget and long lead material | Expedited material, premium cost, possible substitution |
| After the schedule freeze | Only float inside the window | Estimate, material, labour and sequence | Another job is displaced, or the window extends |
| During execution | Only what the crew on site can reach | Everything | Highest cost per hour of work, and the largest risk to the critical path |
Common questions
When does scope freeze happen in a turnaround.
What is the difference between scope freeze and design freeze.
Can work be added after the freeze.
What is emergent scope.
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