Understanding and Identifying the Critical Path in EPC Projects

Understanding and Identifying the Critical Path in EPC Projects

The Line of Logic That Decides Everything

Every EPC project moves forward on two timelines.

The first is visible.

It is made of drawings, deliveries, workfronts, manpower, inspections, and weekly progress reports. Teams track it carefully. It feels tangible and familiar.

The second timeline is invisible.

It is made of logic, sequence, and dependencies. It exists beneath the surface of the project, shaping progress whether anyone notices or not. This invisible timeline is the critical path.

It governs the earliest completion date. It identifies where delay matters and where it does not. It shows where the project is most vulnerable and where decisions have the greatest impact.

Yet on many EPC projects, the critical path is spoken of more than it is understood. Reports highlight it.Meetings mention it. Everyone refers to it. But when asked to explain what truly drives completion, project teams often give different answers.

This should not surprise us. Critical paths are easy to describe and difficult to demonstrate. Schedulers stare at tangled logic. Planners scroll through thousands of activities. Managers rely on simplified reports. And somewhere inside that complexity lies the true sequence that controls the project’s finish date.

Schedules fail not because the logic is incorrect, but because the assumptions beneath the logic are never examined- Keith Pickavance

His point is simple and practical. A project cannot manage what it cannot see.

The purpose of this article is to make the critical path visible. Not by using complex scheduling techniques, but by explaining the principles that allow EPC teams to identify the true driver of completion. When the critical path can be explained, it becomes a tool of foresight. When it cannot be explained, it becomes a risk.

A clear critical path is not a technical luxury. It is the line of logic that allows a project to understand itself.

1. Why Critical Path Identification Fails in EPC Projects

1.1 EPC schedules contain overwhelming complexity

Engineering, procurement, construction, and commissioning each operate on their own timelines. Each contains hundreds or thousands of activities. When combined into a single schedule, this complexity makes the critical path difficult to see.

This is not a planning failure. It is the natural structure of EPC work.

1.2 The software’s “critical” filter is not the true critical path

Primavera and other CPM tools highlight activities based on internal settings. These settings depend on:

• calendars

• progress calculation modes

• constraints

• incomplete logic

• float thresholds

• relationship types

The software shows what it is told to show. It does not understand constructability. It does not understand the real sequence of work.

The critical path in the tool may not be the critical path in the field.

1.3 Schedule quality issues create false criticality

Schedules often contain quality deficiencies that distort float and logic:

• open-ended activities

• missing predecessors or successors

• excessive constraints

• incorrect calendars

• activities outside working periods

• unmodelled scope

• wrong progress settings

The SCL Protocol identifies these issues as primary causes of misleading critical path behaviour. AACE RP 29R 03 lists them as conditions that invalidate forensic analysis.

A schedule with these defects cannot reveal the true critical path.

1.4 EPC projects typically have multiple critical and near critical paths

Process units, utilities, offsites, pipe racks, buildings, and commissioning sequences may each have a path that finishes close to the contractual milestone.

It is normal for an EPC project to have several important drivers. Understanding how they behave is essential to identifying the true controlling sequence.

1.5 Criticality shifts as the project advances

Progress changes logic. Design changes alter sequences. Delivery variations affect relationships. Delays in one area create pressure in another.

Without continuous validation, the critical path seen at the start of engineering may not be the same during construction or commissioning.

This is how projects lose sight of what truly drives completion.

2. What Happens When the Critical Path Is Misidentified

2.1 Strategic decisions lose accuracy

Without a clear critical path, teams focus on visible workloads rather than logical drivers. Acceleration may be attempted in non critical areas. Mitigation may be applied without effect. Management attention becomes reactive.

The project moves, but just not in the right direction...

2.2 Progress reporting becomes misleading

When the critical path is unclear:

• early warnings lose meaning

• forecasts become unreliable

• reports show progress but not causation

• meetings focus on activity rather than sequence

Progress becomes movement without insight.

2.3 Delay analysis becomes vulnerable

Delay claims rely on one evidential foundation:

Did the event delay the critical path?

If the critical path is wrong, the delay analysis cannot be defended.

Nicholas Gould has emphasised on multiple occassions, that causation can only be proven if the logic of the critical path is transparent and traceable. A misidentified path destroys entitlement by breaking the causal chain.

2.4 Contractor and owner lose alignment

The contractor may present one view of the drivers.The owner may believe another.

This misalignment leads to disagreement, dispute, and late escalation. A shared understanding of the critical path prevents this breakdown.

2.5 Schedule instability increases risk

False criticality or hidden criticality results in:

• poor early warning

• confused mitigation

• misallocated resources

• distorted perceptions of progress

• inaccurate claims preparation

The schedule loses its value as a management tool.

3. What EPC Teams Need to Establish a Defensible Critical Path

3.1 A CPM model that reflects actual execution

A critical path is credible only when the underlying model reflects reality.It must include:

• complete scope

• correct activity relationships

• consistent calendars

• justified constraints

• appropriate durations

Roger Gibson has noted that schedules must reflect how work will be built, not how the modeller wishes it to be built. Logic must follow constructability.

3.2 Meaningful float that reflects true sequencing

Float becomes a useful indicator of criticality only when the schedule is clean. This requires:

• removal of open ends

• correction of calendar conflicts

• reduction of unnecessary constraints

• validation of logic

When float reflects reality, the critical path becomes visible.

3.3 A clear chain of driving predecessors

A critical path is defensible when it can be explained. The sequence must be traceable:

• activity by activity

• predecessor by predecessor

• back to the data date

AACE RP 29R 03 and the SCL Protocol both emphasise logic tracing as the basis for reliable analysis.

3.4 A schedule basis that records modelling assumptions

The Schedule Basis Memorandum must document:

• calendars

• shift patterns

• work cycles

• constraints

• logic rules

• progress mode

• data sources

Delay analysis depends on the integrity and transparency of assumptions. Without this, the critical path cannot be defended- David Barry

3.5 Alignment between contractor and owner

A shared critical path prevents misunderstanding and unnecessary conflict. It creates:

• faster decision making

• clearer early warnings

• better risk management

• more credible forecasts

• more straightforward claims resolution

John Uff QC stressed that fairness in administration flows from disciplined record keeping, not retrospective interpretation.

Alignment is that discipline in practice.

4. Evidence Required to Defend the Critical Path

4.1 A transparent logic trace

The critical path must be shown clearly, without reliance on software filters. This is the backbone of defensible delay analysis.

Records and logic must speak for themselves, because narrative cannot replace evidence- Andy Hewitt

4.2 A readable critical path summary

Senior management, owners, and engineers must be able to understand the path within minutes.

A good summary highlights:

• the last finishing activity

• the main chain of drivers

• intermediate merge points

• secondary paths

• near critical behaviour

Clarity creates confidence.

4.3 Correction of CPM modelling issues

Before identifying the path, the model must be corrected. This includes:

• logic validation

• calendar alignment

• removal of open ends

• reduction of constraints

• verification of scope completeness

A flawed model cannot produce a reliable path.

4.4 Correlation with major project documents

The critical path must align with:

• FEED documentation

• execution plans

• milestone strategies

• procurement sequencing

• construction methodology

A mathematical path that does not match operational reality cannot be defended in delay analysis.

Clear, Simple, Educative

What the Critical Path Really Means

The critical path is the chain of work that controls the finish date. Delay here delays the project.Delay elsewhere may not.

Why EPC Projects Often Have Several Critical Paths

Large industrial projects operate across many parallel areas. Several paths may finish close to each other.All require attention.

Why Near Critical Paths Must Be Tracked

A path with little float can overtake the main path quickly. Monitoring only the main path is insufficient.

Why Software Settings Influence What Appears Critical

Calendars, constraints, progress modes, and logic completeness all influence what the tool highlights. Understanding these influences prevents misinterpretation.

Tailpiece

A project schedule is not simply a chart of activities. It is the written logic of how the work must unfold. The critical path is the line within this logic that reveals where time is most vulnerable.

When EPC teams understand the critical path, they understand the project. They know where to focus, how to prepare, and how to protect entitlement. They prevent confusion, reduce conflict, and strengthen decision making.

A clear critical path is not a guarantee of success. But without it, success becomes uncertain.

When teams understand the critical path, they do not merely build the project.

They understand its logic.