As-built drawings are engineering drawings that reflect the condition of a structure, system or piece of equipment exactly as it was constructed — capturing every deviation from the original design intent that was made during fabrication, installation or commissioning. They are the authoritative record of what is physically present in a plant, and form a critical part of the operating documentation set.
In brownfield projects — modifications, expansions or integrity work on existing operating facilities — accurate as-built drawings are the starting point for engineering. Without them, engineers working on modifications are designing blind, and integrity teams cannot verify clearances, pipe routing or structural configurations without physical survey work.
Why As-Built Drawings Diverge from IFC Drawings
In any construction project, the Issued-for-Construction (IFC) drawing set represents the design intent at the point of issue. Field conditions always cause some deviations:
- Pipe routing changed to avoid clashes discovered during fabrication or erection
- Nozzle orientations adjusted because the vessel was rotated during setting
- Equipment relocated within a bay because civil foundations were slightly off-position
- Additional supports, gussets or brackets added on-site
- Valve or instrument positions shifted to improve access
- Material substitutions made when specified material was unavailable — different wall schedule, alternate fitting type
These deviations are tracked during construction using redline mark-ups — printed copies of the IFC drawings on which the site engineer marks changes in red pen. If redlines are not captured in real time, as-built accuracy degrades because deviations are not remembered after the work is buried, insulated or painted.
The Redline to As-Built CAD Conversion Process
Stage 1 — Redline Collection and Review
Redline drawings are collected from the site construction team and consolidated by drawing number. A completeness check verifies that all drawings in the IFC set have a corresponding redline (or a confirmed "no change" notation). Missing redlines must be resolved before CAD work begins — either by obtaining the information from the site team or by field survey.
Stage 2 — CAD Revision
A draughtsman implements the redline changes on the digital CAD drawing. Each change is recorded in the revision history block. The drawing title block is updated to the as-built revision designation (typically "AS-BUILT" added to the revision suffix). Dimensional annotations that were changed on site are updated on the drawing. Where routing has changed significantly, affected sections of the drawing are redrawn.
Stage 3 — Quality Check
A checker — ideally an engineer who did not produce the drawing — reviews the updated CAD drawing against the redline mark-up and verifies:
- All redline changes are incorporated correctly
- Revision cloud is correctly positioned around changed areas
- No inadvertent changes were introduced to unchanged areas
- Drawing annotation is consistent and legible
- Title block reflects as-built revision
Stage 4 — Handover Package Compilation
As-built drawings are transmitted to the client as part of the handover documentation package, alongside the MDR, operating procedures, equipment data sheets and certificates. The handover package is typically structured per the client's document control system, with PDF and native CAD files submitted to the document management system.
Special Considerations for Existing Brownfield Plants Without Original Drawings
When a brownfield facility has no original drawings at all — a common situation in plants built decades ago — as-built drawings must be created from scratch through field survey. This is where as-built documentation overlaps with reverse engineering: the plant must be physically measured, sketched and modelled before a drawing can be produced. Our article on reverse engineering for existing plant equipment covers this process in detail.
SLETEC prepares as-built drawings for brownfield projects through our as-built drawing services and brownfield engineering capability. We handle redline-to-CAD conversion, field survey-based drawing creation and handover package compilation for clients in Saudi Arabia and India.