Piping Isometric QA/QC Checklist: 25-Point Verification Before Fabrication Handoff

The primary cause of pipe spool fit-up failure during site construction is dimensional discontinuity on isometric sheets: 1. **Chain Dimensioning vs Overall Dimensions:** Verify that the sum of incremental fitting-to-fitting dimensions matches the overall boundary dimension within zero tolerance. 2. **Coordinate & Elevation Verification:** Verify centerline elevations ($EL +...$) at terminal connections against equipment general arrangement drawings. 3. **Slope Verification:** For lines with gravity drainage or condensate return, confirm that slope ratios (e.g., $1:100$ or $1:500$) are explicitly annotated with flow direction arrows. 4. **Tie-In Coordinates:** Confirm existing plant tie-in point coordinates ($N, E, EL$) against certified tie-in schedules or laser scan point cloud benchmark data.

Every physical component on the isometric drawing must be accounted for in the BOM table: - **Material Descriptions & Wall Thicknesses:** Confirm that pipes, elbows, tees, and reducers match the project Piping Material Specification (PMS). - **Flange Pressure Ratings:** Check that flange ratings ($150\#$, $300\#$, $600\#$) correspond to design pressure and temperature requirements. - **Gasket & Bolting Quantities:** Verify that stud bolt diameters, lengths, and quantities match flange bolt hole counts per ASME B16.5. - **Valve Identification & Tagging:** Verify that valve tag numbers (e.g., `XV-1021`, `FCV-2005`) match P&ID instrument tags.

To enable traceability during fabrication and hydrotest: - **Shop vs. Field Welds:** Verify that field welds are strategically placed to keep spools within transport haulage limits ($12\text{m} \times 2.4\text{m}$). - **Weld Identification Numbers:** Ensure sequential weld numbers are assigned to every butt weld. - **Trimming Allowance:** Confirm that field adjust welds include the mandatory $100$ mm extra pipe length for site alignment adjustments. - **NDE Percentage Requirements:** Ensure that radiographic (RT) or ultrasonic (UT) inspection percentages (e.g., $5\%$, $10\%$, or $100\%$ per ASME B31.3) are designated in the drawing notes.