Pipeline Dent Depth Screening Calculator (Plain Dents, %OD) — Sample Report

1 · Design inputs

An in-line inspection run on an NPS 12 line (12.75 in OD) reports a plain dent on the pipe body, away from any weld, with no associated metal loss and no gouging. Field verification confirms a maximum depth of 0.5 in from the original profile. The operator's procedure applies a 6% of OD plain-dent acceptance limit.

2 · Method

Depth expressed as a percentage of outside diameter, and the margin to the acceptance limit:

depth% = 100 · d / D

margin% = limit% − depth% → PASS when depth% ≤ limit%

where d is the measured maximum inward deviation from the pipe's original circular profile and D the nominal outside diameter, both in the same units — the ratio is dimensionless, so inches, millimetres or any consistent pair all give the same percentage. limit% is the acceptance limit from the code, dent category and pipe size that applies to your line, entered by you.

Two details in that definition do real work. First, the depth is measured from the original profile, not from the lowest surrounding point of the deformed pipe — a dent in an already out-of-round section is measured against where the wall should be, and getting that datum wrong is a common source of disagreement between an ILI report and a field measurement. Second, depth is normalised on the outside diameter, not the wall thickness. A 0.5 in dent is a 6.3% dent on NPS 8 and a 1.6% dent on NPS 30; the same absolute deformation is a completely different disposition on a different line size.

The engine validates that D and limit% are positive and that the depth is non-negative, reports both percentages to three decimals, and returns the verdict. It carries a standing warning on every run: the depth screen covers plain dents only — dents on welds, dents with gouges, cracks or metal loss, and dents in cyclic service all need a strain-based or fatigue assessment regardless of what percentage they measure.

3 · Calculation

1. Normalise the depth on the outside diameter: 0.5 / 12.75 = 0.0392157.
2. Express as a percentage: 0.0392157 · 100 = 3.922% of OD.
3. Compare against the limit: 3.922% ≤ 6%, so the dent clears the screen.
4. Remaining margin: 6 − 3.922 = 2.078% of OD, which on this pipe is 2.078% · 12.75 = about 0.265 in of additional depth before the limit is reached.
5. Verdict: PASS — the dent is acceptable on the depth screen, conditional on it being genuinely plain.

4 · Results PASS

5 · Verification statement

The result values above are locked as fixture dent-screening.json, case “0.5 in dent on NPS 12, 6% limit — passes”, 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: ASME B31.8, Gas Transmission and Distribution Piping Systems — ¶851.4, evaluation and repair of imperfections and damage, including dent acceptance criteria; limit values are user-supplied from the governing edition. · ASME B31.4, Pipeline Transportation Systems for Liquids and Slurries — ¶451.6, disposition of defects including dents; limit values are user-supplied. · ASME B31.8S, Managing System Integrity of Gas Pipelines — dent categorisation, interaction with welds and metal loss, and response criteria. · API RP 1183, Assessment and Management of Dents in Pipelines — strain-based and fatigue assessment methods for dents that fall outside the depth screen. · No acceptance percentage is embedded — the limit is entered by the user from the code, dent category and pipe size that govern the line.