8.2 As-Built Survey, Redline Drawings & Weld Maps

As-Built Survey, Redline Drawings & Weld Maps

Quick Answer: As-built redline drawings are the alignment sheets marked up with as-constructed information — actual stationing, weld and NDE locations, depth of cover, tie-in points, test-lead stations, crossings, and casings. The API 1169 inspector verifies that redlines are maintained during construction and finalized accurately, because the as-built is the operator's legal record of where the pipe actually lies.

The design alignment sheets show where the pipeline was planned to go. The as-built redline shows where it actually went. The gap between the two is what the as-built survey captures, and it is one of the most important back-end records the inspector verifies. Once the line is buried and the right-of-way is restored, the as-built drawings are the only reliable map of what is underground.

Why As-Builts Matter

A buried pipeline is invisible. If a weld fails, the operator must be able to find that exact weld, dig it up, and repair it — which requires knowing the station, the material, the NDE result, and the depth. If a landowner builds a fence, the operator must know exactly where the pipe is to avoid damage. Federal records requirements — 49 CFR § 195.404, "Maps and records," for hazardous liquid, and 49 CFR § 192.605(b)(3) for gas, which requires the operator's O&M manual to cover making construction records, maps, and operating history available to operating personnel — oblige the operator to maintain maps showing the location of facilities, and the as-built redline is the primary source for those maps. An inaccurate as-built is a compliance defect, not just a paperwork problem.

The Redline Process

Redlining is a continuous process, not a one-time end-of-job activity. As each segment of pipe is laid, welded, inspected, and buried, the alignment sheet is marked up with what actually happened at that station. The inspector's role is to verify that the redline is being kept current — if a field change is made (a reroute around an unexpected obstacle, an extra weld cut-out and re-weld, a test-lead moved to a different station), that change is captured on the redline the same day, not reconstructed from memory weeks later.

What Goes on a Redline Alignment Sheet

Weld Maps and NDE Traceability

The weld map is the heart of the as-built. Every girth weld is given a unique number (typically by survey station plus a welder ID or sequence number) and tied to three pieces of data:

1. Station — where the weld is located along the line.
2. Welder — which qualified welder made the weld (per welder qualification log).
3. NDE result — whether the weld passed radiographic (RT) or ultrasonic (UT) inspection, and the report number.

If a weld is cut out and re-made, the cut-out and re-weld are both recorded, with new weld numbers. If a weld is repaired, the repair is recorded against the original weld number. The inspector verifies that the weld map reconciles with the NDE log — every weld that was radiographed must appear on the weld map with its result, and any reject must show a re-weld or repair entry.

Weld Map Integrity Checks

• No gaps — every station between tie-ins must have a continuous chain of welds.
• No duplicates — each weld number is used once only.
• NDE reconciliation — the number of welds equals the number of NDE reports (100% RT/UT) or matches the specified percentage (e.g., 10% random RT).
• Welder ID match — welder numbers on the map match the qualified-welder log.
• Repair traceability — every repair ties back to the original reject.

Depth-of-Cover Verification

Depth of cover is the vertical distance from finished grade to the top of pipe. The alignment sheets specify minimum cover at each station, with deeper cover required at road, rail, and watercourse crossings (typically per the operator's design code or permit). The inspector verifies depth of cover is measured and recorded:

• At specified intervals (often every weld or every surveyed station).
• At every crossing.
• At any location where the ditch was deepened or the grade was raised.
• After final grading, not before — because final grade determines the actual cover.

Where measured cover is less than the specified minimum, the pipe must be either re-lowered, protected with mechanical cover (concrete slab, extra casing), or the design must be re-evaluated. The inspector records any cover deficiency and the resolution.

Crossings and Casings

At road, rail, and some utility crossings the pipeline may be installed inside a casing — a larger pipe that carries the carrier pipe through the crossing. The as-built records:

• Casing material, diameter, and wall thickness.
• Casing coating.
• Insulators (centralizers that keep the carrier pipe centered in the casing and electrically isolate it).
• End seals (to keep water and soil out of the annulus).
• Vents (where required by code, brought to grade).
• Carrier pipe coating inspection inside the casing before sealing.

The inspector verifies casing installation per spec and that the cased section is electrically isolated from the mainline for CP purposes (a casing short can mask CP readings and is a common as-built defect).

PI/POT (Point of Tie-In) Locations

The PI (Point of Intersection) is a survey point where the pipeline alignment changes direction; the POT (Point of Tie-In) is where the new pipeline connects to an existing facility. Both are recorded on the as-built with actual surveyed coordinates and stationing. At a tie-in, the inspector verifies the tie-in weld is recorded on the weld map with its NDE result, the existing pipe material is compatible with the new, and the tie-in is included in the hydrostatic test boundary (or tested separately if it is the final tie-in that cannot be hydrotested).

Material and Coating Information

The as-built must record the pipe material and coating for each segment, because future integrity digs and repairs need to know what is in the ground. This includes:

• Pipe grade (e.g., API 5L X60) and wall thickness per segment.
• Coating type (FBE, 3LPE, coal tar, etc.) and any coating repairs.
• Bend information (factory vs. field, angle, radius).
• Anomaly or repair locations (dents, gouges, sleeve repairs).

Redline Maintenance During Construction

The inspector verifies that the redline is being maintained concurrently with construction, not assembled at the end. Best practice is the survey crew updates the redline within a day of each completed segment, and the inspector spot-checks the redline against the field reality (welder log, NDE log, survey stakes) at least weekly. A redline that is allowed to fall behind becomes unreliable — once the ditch is backfilled, the only way to verify a missed entry is to re-survey or re-dig.

Final As-Built Deliverable

At the end of construction, the redlines are finalized into a clean as-built set, typically delivered in both paper and GIS/CAD format. The inspector signs off that the as-built is a true representation of what was built, and any field changes that were not on the original design drawings are captured. The finalized as-built becomes the operator's record drawing and feeds the operator's GIS, one-call system, and integrity management program.

Key Takeaways for the Exam

• The as-built redline is the as-constructed record; the inspector verifies it is maintained concurrently and finalized.
• Weld maps tie each weld to station, welder, and NDE result — no gaps, no duplicates, full NDE reconciliation.
• Depth of cover is measured at specified stations and crossings and verified against minimum cover on the alignment sheet.
• Casings must be electrically isolated from the carrier pipe; a casing short is a common as-built defect.
• The finalized as-built feeds the operator's federal records under 49 CFR Part 192/195.