Actual bore uncertainty
Schedule, lining, ovality, deposits, and inspection coverage determine effective diameter.
Engineering
Pipe Sensitivity Calculator
Compare a reviewed pipe with changed internal diameter and roughness at fixed flow, quantifying velocity, pressure-drop, head-loss, and power changes.
PIPE HYDRAULIC SENSITIVITY
Measure how a small bore change can dominate a large roughness change
Head loss responds nonlinearly to diameter because smaller bore raises velocity and L/D together. This calculator holds flow, length, fluid, and fittings constant, then changes diameter and roughness explicitly. It reports both full cases instead of one untraceable sensitivity percentage.
Base head loss (m)—
Changed head loss (m)—
Head-loss change—
Pressure-drop change (kPa)—
Velocity change—
Hydraulic power change (kW)—
PIPE HYDRAULIC SENSITIVITY
Base-versus-changed hydraulic ledger
Use the comparison to rank inspection and design uncertainty. A severe plausible response can justify measurement or cleaning evaluation; it does not prove degradation exists.
| Case | Internal diameter (mm) | Roughness (mm) | Velocity (m/s) | Head loss (m) | Pressure drop (kPa) |
|---|
CURRENT CALCULATION PROCESS
Formula, substitution, intermediate values, and reconciliation
For each case: v=Q/A; Re=rho v D/mu; hL=[f(L/D)+K]v^2/(2g); sensitivity=(changed-base)/base
Both cases recalculate velocity, Reynolds number, friction factor, and loss. The model avoids a fixed diameter-power shortcut.
| Input / symbol | Engineering meaning and unit | Current value |
|---|---|---|
| flowM3h | Fixed comparison flow (m3/h) — Same in both cases | 140 |
| baseDiameterMm | Base internal diameter (mm) — Reviewed reference bore | 200 |
| diameterChangePercent | Internal diameter change (%) — Negative for fouling or smaller bore | -5 |
| lengthM | Pipe length (m) — Held constant | 600 |
| baseRoughnessMm | Base absolute roughness (mm) — Reference wall condition | 0.045 |
| roughnessMultiplier | Changed roughness multiplier — Changed divided by base | 4 |
| density | Fluid density (kg/m3) — Held constant | 998 |
| dynamicViscosityMpaS | Dynamic viscosity (mPa*s) — Held constant | 1.002 |
| minorK | Unchanged minor-loss coefficient K — Same component basis | 8 |
Intermediate values remain unrounded until display formatting.
HOW TO USE THIS MODEL
Run one controlled sensitivity at fixed flow
- Start from reviewed bore, roughness, length, fittings, fluid, and flow.
- Enter diameter change from schedule, lining, fouling, or inspection evidence.
- Enter roughness multiplier from material or condition evidence.
- Hold flow and fluid fixed to isolate geometry; run separate demand scenarios.
- Compare velocity, head, pressure, and power, then target the governing uncertainty.
PIPE HYDRAULIC SENSITIVITY FUNDAMENTALS
Why diameter and roughness sensitivities differ
- Bore reduction
- Decrease in internal area from schedule, lining, scale, deposits, or deformation.
- Roughness growth
- Wall irregularity increase changing turbulent friction.
- Fixed-flow comparison
- Same flow so geometry is not confused with demand.
- Nonlinear response
- Velocity and L/D change together.
- Sensitivity ratio
- Relative output change, not probability.
- Hydraulic power delta
- Power change due only to changed loss at fixed flow.
MODEL AND FORMULA
Recalculate Reynolds number and friction factor in both cases
For each case: v=Q/A; Re=rho v D/mu; hL=[f(L/D)+K]v^2/(2g); sensitivity=(changed-base)/base
Both cases recalculate velocity, Reynolds number, friction factor, and loss. The model avoids a fixed diameter-power shortcut.
DEEPER ENGINEERING ANALYSIS
Evidence questions behind a severe result
Roughness calibration
Published values may not represent aged, coated, biofouled, or blocked pipe.
Demand feedback
A real fixed-speed pump may deliver less flow when resistance rises; actual operation needs the system intersection.
WORKED DECISION CASES
Two responsible uses of sensitivity
Fouling inspection priority
A plausible bore loss sharply raises required head, supporting targeted inspection and cleaning evaluation.
Schedule comparison
Alternative schedules change bore and recurring energy before pressure and lifecycle costs are considered.
TECHNICAL LANGUAGE
Pipe sensitivity glossary
- Scenario variable
- Input deliberately changed.
- Controlled variable
- Input held fixed.
- Hydraulic diameter
- Characteristic flow dimension.
- Relative roughness
- Roughness divided by diameter.
- Head-loss gradient
- Head loss per unit length.
- System resistance
- Combined friction, local, static, and equipment demand.
EVIDENCE AND DATA LINEAGE
Retain the reason for every changed input
Keep base model, bore and lining source, fouling evidence, roughness source, fluid condition, fixed-flow rationale, fittings, changed-case provenance, unrounded ledgers, and the decision informed.
LIMITS AND EXCLUSIONS
What deterministic sensitivity does not predict
- No probability, confidence, or degradation timeline is calculated.
- No changed pump-system operating flow, control, equipment, thermal, two-phase, non-Newtonian, or transient behavior is solved.
- No integrity, remaining wall, cleaning feasibility, erosion, deposition transport, or code assessment is provided.
RELIABLE SOURCES
References for this page's method and boundaries
FREQUENTLY ASKED QUESTIONS
Questions about diameter and roughness comparison
Why hold flow constant?
It isolates head needed to preserve service; actual flow may change and needs system analysis.
Can diameter change be negative?
Yes within the model boundary when physically justified.
Why not use a fifth-power rule?
The calculator recalculates friction factor and minor losses.
Does four times roughness mean four times loss?
No. Roughness acts through relative roughness and friction factor.
Can this predict remaining life?
No. It contains no time or probability model.
What if loss decreases?
Verify minimum velocity, control, capital, and service constraints.
RELATED CALCULATORS
Continue the engineering review
Use these follow-on models to test a different boundary without hiding it inside this calculation.
IMPORTANT ENGINEERING NOTE
Use sensitivity to target evidence, not invent degradation
Final operating, inspection, cleaning, replacement, and energy decisions require verified condition data, full system behavior, integrity and lifecycle assessment, and qualified review.