5.1 Stringing, Material Identification & Handling

5.1 Stringing, Material Identification & Handling

Quick Answer: Stringing is the controlled distribution of pipe along the right-of-way (ROW) per the pipe tally and alignment sheet so that the correct wall thickness, grade, and coating land at the right station. The inspector verifies each joint against its Mill Test Report (MTR)/Mill Test Certificate (MTC), checks for shipping and handling damage, confirms proper handling equipment (nylon slings, padded forks — never bare chains on coated pipe), and reports any discrepancy before the pipe is committed to the trench.

What "Stringing" Means on a Pipeline Spread

Stringing is the first construction activity in API 1169 Body of Knowledge Area 3 — Installation Construction, the largest BOK area (an unofficial practice-weighted estimate near 36%). After pipe is trucked from the mill or coating yard to the ROW, each joint is laid out along the surveyed centerline in the sequence the line will be built. The driver document is the pipe tally (also called the joint tally), cross-referenced to the alignment sheet. The alignment sheet tells the crew, station by station, what wall thickness, grade, and coating is required — for example, a heavier wall at a road crossing, a class-location change, or a directional-drill tie-in. If a joint lands at the wrong station, a pressure boundary can be built with the wrong material; the inspector's job is to prevent that.

Material Identification: Verifying the Joint Against the MTR/MTC

Every joint arrives with a Mill Test Report (MTR) or Mill Test Certificate (MTC). Before the joint is accepted into the string, the inspector confirms the markings on the pipe match the MTR and the alignment-sheet requirement for that station:

If any attribute is missing, illegible, or inconsistent with the MTR, the joint is quarantined — set aside and tagged — until the discrepancy is resolved in writing.

Defect and Damage Inspection

Pipe can be damaged in transit, in handling, or while stacked on the ROW. The inspector walks each load and joint and looks for:

• Dents — any visible indentation; dents in the weld seam or exceeding code depth limits are rejectable.
• Gouges and grooves — metal removal that thins the wall or concentrates stress; grind out and verify remaining wall.
• Arc burns — stray electrical arc strikes (often from ground clamps) that create hard, crack-prone spots; must be ground smooth and inspected.
• Coating damage — holidays, disbondment, lapping wrinkles, or bare spots; repaired per the coating specification before lowering-in.
• Lamination indications — visible surface separations; hold for engineering review.
• End/bevel damage — deformed bevels prevent proper fit-up; re-bevel or cut back.

Handling Equipment and Stacking Rules

How pipe is moved and stored on the ROW is itself an inspectable item:

• Lift with nylon or web slings, padded forks, or cradles — never bare chains, cables, or hooks directly on coated pipe, which cut the coating and dent the steel.
• Dunnage between layers — timber dunnage of the right size, placed so weight is distributed and bevels are protected.
• Stack height limits — follow the project pipe-handling specification (commonly 3–4 layers for large-diameter pipe); excessive stacks deform the bottom joints and risk rolling.
• End protection — bevel protectors stay on until just before welding; the inspector checks they are present and undamaged.
• Weather protection — keep FBE-coated pipe out of prolonged sun where the spec requires tarping; keep bevels dry before welding.
• Support spacing — dunnage placed close enough to the ends to prevent sagging and to keep the pipe round.

Reporting Discrepancies

The inspector does not approve "use as is" for off-spec material. When a discrepancy is found:

1. Tag the joint as "HOLD — discrepancy" and record the joint number, heat, station, and the nature of the issue.
2. Notify the contractor and company representative in accordance with the project inspection plan.
3. Document on the daily inspection report and, where the project uses one, a nonconformance report (NCR).
4. Do not release the joint until the discrepancy is dispositioned in writing (use-as-is, rework, or reject).

Key Takeaways Recap

• Stringing places the right pipe at the right station per the pipe tally and alignment sheet.
• MTR/MTC verification closes the traceability loop from mill heat to finished weld.
• Chains on coated pipe are a classic handling violation; nylon slings and padded forks are required.
• Discrepancies are held, tagged, and dispositioned in writing — never silently accepted.