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 applies a combined usage factor of 0.72, and the line operates at 1,440 psi.

2 · Method

The single-defect capacity form for a longitudinal metal-loss defect under internal pressure. 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 capacity (best-estimate burst) pressure of the defected section:

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

and the safe working pressure and utilization:

P_sw = usage factor · P_cap

utilization = P_op / P_sw → PASS when utilization ≤ 1

Read the capacity 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 and the usage factor positive, and the operating pressure non-negative. Entering P_op = 0 puts the card in capacity-only mode: it returns P_cap 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 standing warning fires above d/t = 0.85, outside the validated range of the single-defect equation, and every 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. Capacity pressure: P_cap = 4,042.424 · 0.76831 = 3,105.826 psi.
8. Safe working pressure: P_sw = 0.72 · 3,105.826 = 2,236.194 psi.
9. Utilization: 1,440 / 2,236.194 = 0.64395 → the line runs at about 64% 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, usage 0.72”, tolerance 0.05, 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 — Part B allowable-stress capacity form for a single longitudinal metal-loss defect under internal pressure, including the length correction factor Q. Usage/safety factors and the tensile strength basis 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 — all are entered by the user.