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.
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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 Each assumes the drawing reflects the current plant, so an out-of-date as-built feeds error directly into safety studies and project scope.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.
Frequently asked.
What is the difference between an IFC drawing and an as-built.
An issued-for-construction, IFC drawing shows the design intent the field builds to. An as-built shows what was actually installed, with field changes incorporated. The as-built is the IFC plus every change made during construction and commissioning.
What is a redline drawing.
A redline is a drawing marked up by hand in the field to record where the build differs from the design. Redlines are the raw input to the as-built. Once incorporated and reissued, they become the as-built revision.
Why are as-built P&IDs often out of date.
Because redlines are not always incorporated and later modifications go in without reissuing the drawing. The master as-built then lags the plant, which is the common brownfield situation of an old revision on the wall and a changed plant in the field.
Who is responsible for maintaining as-builts.
Document control owns the revision cycle, but engineering and construction supply the redlines and the change records. Keeping the as-built current depends on those changes being captured and reissued under control rather than left as loose markups.