As-built drawing.
An as-built drawing is the revision of a drawing updated to reflect what was actually constructed and installed in the field, incorporating the redline markups made during construction and commissioning. For a P&ID, the as-built is the version that matches the plant as it currently stands, not the issued-for-construction intent.
What As-built drawing means.
A drawing passes through several states on its way to being an as-built. It is issued for construction, marked up in the field as the build deviates from the design, and finally reissued with those redlines incorporated as the as-built revision. The persistent problem in operating plants is the gap between the drawing on the wall, often an old revision, and the plant in the field, which has moved on through modifications that were never folded back into the master. Every later activity, a modification, a management-of-change, a HAZOP, a decommissioning study, starts from the as-built, so when the as-built lags reality the error propagates into all of them. Keeping as-builts current is a document-control discipline. Redlines are captured, incorporated, and reissued under a controlled revision cycle, and the master register records which revision is the truth. A register that reconciles against the latest revision, with each tag traceable to the sheet it came from, is what keeps the as-built honest.
From IFC to as-built
A drawing is issued for construction, IFC, marked up in the field as the build deviates from the design, then reissued as the as-built with those redlines incorporated. The as-built is the record of what was actually installed, as distinct from what was designed.
Why as-builts drift from reality
Redlines are often never incorporated, and later modifications go in without reissuing the drawing, so the official as-built falls behind the plant. This is the rev-on-the-wall versus rev-in-the-field problem that makes brownfield work slow and risky.
What as-builts are used for
Modifications, management of change, HAZOP studies, and decommissioning all begin from the as-built. Each assumes the drawing reflects the current plant, so an out-of-date as-built feeds error directly into safety studies and project scope.
As-built and document control
Maintaining as-builts is a controlled process. Redlines are captured, incorporated, and reissued on a defined revision cycle, with a master register recording the current revision. Holding a single current baseline is what stops competing copies of the truth from circulating.
Common questions
What is the difference between an IFC drawing and an as-built.
What is a redline drawing.
Why are as-built P&IDs often out of date.
Who is responsible for maintaining as-builts.
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