How to Prepare an Industrial Piping Bill of Quantities (BOQ): MTO & Cost Estimation
An accurate Bill of Quantities (BOQ) is the commercial and technical bedrock of any industrial piping project. Vague descriptions or missing line items lead to costly variation claims, material shortages, and project delays. This guide provides a comprehensive methodology for preparing an engineered piping BOQ from P&IDs and isometric drawings.
1. The Material Take-Off (MTO) Process
Preparing a piping BOQ begins with the Material Take-Off (MTO). Our estimating engineers extract material requirements from Process & Instrumentation Diagrams (P&IDs), piping layout plans, and isometric drawings:
- Straight Pipe: Quantified in linear meters, segregated by Nominal Pipe Size (NPS), material specification, and schedule/wall thickness.
- Fittings: Quantified by count, listing component type (90° LR elbow, equal tee, concentric reducer), schedule, and material grade.
- Flanges: Listed by count, pressure class (150# to 2500#), facing type (RF, RTJ), and bore schedule.
- Valves: Specified by size, class, body material, trim material, end connection, and actuation mechanism (manual lever, gear, pneumatic, electric).
- Flange Hardware: Gaskets and stud bolts with heavy hex nuts, categorized by diameter, length, and coating.
2. Standard Line Item Description Structure
A technically complete BOQ line item must contain seven distinct parameters:
[Item] - [Size] - [Rating/Schedule] - [Standard] - [Material Spec] - [End Prep] - [Certification]
Example: "Pipe, NPS 6", Schedule 40 (7.11mm WT), ASME B36.10M, ASTM A106 Gr. B Seamless, Beveled Ends (ASME B16.25), EN 10204 Type 3.1 MTC, Quantity: 250 Meters."
3. Quantifying Fabrication & Welding: The Diameter-Inch (Dia-Inch)
Material supply is priced per meter or piece, but shop prefabrication and field welding are universally estimated using Diameter-Inches (Dia-Inch) or Diameter-Millimeters:
Dia-Inch = Nominal Pipe Size (Inches) * Number of Circumferential Butt Welds
Example: Welded joint on an NPS 8" pipe = 8 Diameter-Inches. If a spool contains 4 butt welds on 8" pipe, the fabrication scope equals 32 Diameter-Inches.
Estimators apply difficulty factors to baseline dia-inch rates based on wall thickness (Schedule 80 vs Sch 40), metallurgy (Duplex requires ~2.5x the man-hours of Carbon Steel), and welding position (1G rolled vs 6G field weld).
4. Non-Destructive Testing & Pressure Testing Scope
A common error in amateur BOQs is omitting testing scopes. A professional BOQ includes separate line items for:
- Volumetric weld NDT: Specified as percentage of total butt welds (e.g. "5% RT on Normal Fluid Service" or "100% PAUT on Category M lines").
- Positive Material Identification (PMI): Count of alloy components and weld verification points.
- Hydrostatic Pressure Testing: Man-hours and equipment for test pack filling, pressurization, holding, draining, and drying.