DNV-RP-F101 Corroded Pipe Calculator (Single Defect Capacity) — Sample Report

1 · Design inputs

An NPS 12 line, 12.75 in OD × 0.375 in wall in API 5L X52 material, with the assessment run on a tensile strength of 66,700 psi. In-line inspection reports an isolated longitudinal metal-loss defect 6 in long with a maximum depth of 0.15 in — 40% of the wall. The assessment enters F1 = 0.9, the Part B modelling factor, and an F2 (design factor) of 0.72, and the line operates at 1,440 psi.

2 · Method

The Part B single-defect method for a longitudinal metal-loss defect under internal pressure only (Sec.4.3.2). First the length correction, which converts the defect's slenderness relative to the pipe's characteristic length √(D·t) into a capacity reduction:

Q = √( 1 + 0.31 · ( ℓ / √( D · t ) )² )

Then the failure pressure of the defected section — Part B's Step 1, with no 1.05 factor (the Sec.2.1 mean-capacity equation is 1.05 × this):

P_f = ( 2 · t · f_u / ( D − t ) ) · ( 1 − d/t ) / ( 1 − (d/t) / Q )

and the safe working pressure and utilization, per DNV-RP-F101 Part B, the allowable-stress approach:

F = F₁ · F₂ (F₁ = Part B Modelling Factor; F₂ = Operational Usage Factor, normally your design factor — both entered by you)

P_sw = F · P_f

utilization = P_op / P_sw → PASS when utilization ≤ 1

Read the failure-pressure equation as three factors. The leading term 2·t·f_u/(D−t) is the burst pressure of sound pipe in the mean-diameter form — note the (D−t) denominator rather than D, which is not the Barlow thin-wall form and gives a slightly higher number. The (1 − d/t) numerator is the fraction of wall the defect leaves behind. The (1 − (d/t)/Q) denominator is where length enters: a very short defect has Q ≈ 1, the two terms nearly cancel, and the capacity approaches sound pipe; a long defect has a large Q, the denominator approaches 1, and the capacity collapses toward the plain (1 − d/t) fraction of the sound-pipe burst — the infinitely-long-defect limit, where the remaining ligament simply carries the hoop load on its own.

Inputs are validated rather than trusted: D and t positive with t < D/2, the defect depth strictly less than the wall (a through-wall defect is a leak, not an assessment), f_u, F₁ and F₂ positive, and the operating pressure non-negative. F₁ has no default: the card computes nothing until you enter it from your own copy of the recommended practice. Entering P_op = 0 puts the card in capacity-only mode: it returns P_f and P_sw and suppresses the verdict, which is what you want when you are establishing what a defect can carry rather than checking it against a known pressure. A measured depth over 85% of the wall (d/t > 0.85) is not accepted by RP-F101 (Sec.4.3.2): the card returns FAIL with that reason and no failure or safe working pressure, whatever the operating pressure. Every accepted run is flagged as applying to an isolated defect only.

3 · Calculation

1. Characteristic length: √(D·t) = √(12.75 · 0.375) = √4.78125 = 2.18661 in.
2. Normalised defect length: ℓ / √(D·t) = 6 / 2.18661 = 2.74398.
3. Length correction: Q = √(1 + 0.31 · 2.74398²) = √(1 + 0.31 · 7.52941) = √3.33412 = 1.82596.
4. Depth ratio: d/t = 0.15 / 0.375 = 0.4.
5. Sound-pipe term: 2·t·f_u / (D − t) = 2 · 0.375 · 66,700 / (12.75 − 0.375) = 50,025 / 12.375 = 4,042.424 psi.
6. Defect factor: (1 − 0.4) / (1 − 0.4/1.82596) = 0.6 / (1 − 0.21906) = 0.6 / 0.78094 = 0.76831.
7. Failure pressure: P_f = 4,042.424 · 0.76831 = 3,105.827 psi.
8. Total usage factor: F = F₁ · F₂ = 0.9 · 0.72 = 0.648.
9. Safe working pressure: P_sw = F · P_f = 0.648 · 3,105.827 = 2,012.576 psi.
10. Utilization: 1,440 / 2,012.576 = 0.71550 → the line runs at about 72% of the defect's safe working pressure, so the verdict is PASS.

4 · Results PASS

5 · Verification statement

The result values above are locked as fixture dnv-f101-defect.json, case “NPS 12 t=0.375 X52 (fu=66700), d/t=0.4, l=6 in, F2=0.72 design factor, F1=0.9 entered (Part B modelling factor)”, tolerance 0.001, in the calc-core continuous verification gate (see https://pipingtoolset.com/trust/validation.html). Allowable-stress and factor data are user-supplied inputs; citations: DNV-RP-F101, Corroded Pipelines (September 2019, amended September 2025), Part B (allowable-stress approach), Sec.4.2–4.3.2 — failure pressure and safe working pressure of a single longitudinal metal-loss defect under internal pressure, the 85% measured-depth acceptance limit, including the length correction factor Q and the F = F1·F2 usage-factor split. F1 is Part B's modelling factor (0.9 in the edition the worked example follows); it, F2, the tensile strength basis and every other factor are user-supplied from the governing revision. · ASME B31G, Manual for Determining the Remaining Strength of Corroded Pipelines — the alternative method, built on a yield-derived flow stress and the Folias factor; see the B31G calculator for the same defect assessed that way. · API 5L, Line Pipe — source of the specified minimum tensile strength; whether the assessment uses specified minimum or actual certified values is set by the assessment route, not by this tool. · ASME B31.8S, Managing System Integrity of Gas Pipelines — where a remaining-strength assessment sits within an integrity management programme, and the basis for re-inspection intervals that this calculation does not set. · No usage factor, safety factor or material value is embedded — F1, F2, fu and everything else are entered by the user from the governing revision of DNV-RP-F101. The equation form, including its 0.31 length-correction coefficient and the 0.85 depth limit, is in the code.