API 579 Part 12 Dent and Gouge Assessment Screening

API 579 Part 12 Dent and Gouge Assessment is used when mechanical damage affects pressure equipment and the integrity decision is controlled by local deformation and surface damage—not corrosion rate. Dents, gouges, and dent-gouge combinations can introduce high local stress and fatigue sensitivity, especially near welds, nozzles, attachments, or in cyclic service.

Use this screening workflow to confirm Part 12 applicability and whether your damage measurements are sufficient to support a defensible evaluation. In many cases, a formal Part 12 assessment is needed to determine whether the damaged area is acceptable for continued service, whether operating restrictions are required, and whether repair timing should be immediate or deferred to a planned outage.

Use the screening questions below to determine whether a formal Part 12 evaluation is recommended.

API 579 Part 12 — Dents, Gouges, and Dent-Gouge Combinations (Screening + Assessment Path)

Instruction: Answer all questions (use N/A when the item truly does not apply), then click “Check next step”.

A) Confirm Part 12 Applies (Damage Type & Scope)

1) Is the observed damage a dent (inward deviation) in a shell/cylinder (not a bulge/out-of-roundness issue)?
For example; a forklift impact created a local “push-in” on a pipe spool or vessel shell.
2) Is the observed damage a gouge (elongated material removal/relocation; length ≫ width) causing wall loss?
For example; excavation equipment scraped the pipe, leaving a long narrow metal-loss track.
3) Is this a dent-gouge combination (a gouge inside the deformed dent region)?
For example; an impact pushed in the pipe and the contact edge also “cut” a groove at the dent base.
4) If there are other flaw types (crack-like indications, laminations, HIC/SOHIC, blister networks, etc.), will those be evaluated by the appropriate API 579 Part(s) (not “forced” into Part 12)?
For example; UT shows lamination near the dent—treat lamination per Part 13 instead of only Part 12.

B) Level 1 / Level 2 Applicability Checks (If “No”, expect Level 3 / repair / rerate)

5) Is the component NOT operating in the creep range (temperature regime requiring Part 10 creep evaluation)?
For example; hot reformer outlet piping in creep range → do not rely on Part 12 Level 1/2 alone.
6) Was the original design basis per a recognized code/standard (so code allowable stress concepts apply)?
For example; ASME VIII / B31 piping is “Yes”. A one-off proof-tested geometry is not ideal for Level 1/2.
7) Do you have confidence the material has sufficient toughness for this service (or will you complete brittle-fracture screening per Part 3 if uncertain)?
For example; unknown vintage carbon steel at low metal temperature → do Part 3 brittle-fracture screening.
8) Is the component loading internal pressure only (supplemental + thermal loads negligible for Level 1/2)?
For example; significant nozzle loads, pipe bending, or thermal gradients → Level 3 is typically needed.
9) Is the damaged region on a cylindrical shell whose geometry meets Part 12 Level 1/2 bounds (diameter/thickness/radius limits per the Part 12 equations)?
For example; very small diameter tubing or very thick-wall geometry outside stated bounds → Level 3.
10) Is the material carbon steel meeting the Level 1/2 strength limits (SMYS limit for static dent-gouge; UTS limit for fatigue screening)?
For example; high-strength linepipe grade above the stated SMYS limit → treat as outside Level 1/2 scope.
11) Is the dent NOT kinked/sharp, i.e., does the sharpest local radius satisfy the Part 12 criterion (dent radius not too tight)?
For example; a sharp crease (kink) at the dent edge is a red flag → Level 3 / repair likely.
12) Are dents/dent-gouges isolated (not closely spaced / interacting)?
For example; multiple dents in a cluster from repeated impacts may interact → Level 3 needed.
13) For a dent-gouge combination, is the gouge orientation longitudinal (axial) (not circumferential)?
For example; a circumferential gouge in a dent is outside Level 1/2 and typically requires Level 3.
14) Is the component not in cyclic service for Level 1 screening (e.g., fewer than ~150 cycles total or passes Part 14 cyclic screening)?
For example; frequent pressure swings each shift → treat as cyclic service → Level 2 fatigue check or Level 3.

C) Data & Measurements Readiness (If “No”, you’re not ready to conclude acceptability)

15) Do you have the original equipment design data needed to define MAWP inputs (dimensions, nominal thickness, material spec, corrosion allowance/FCA, etc.)?
For example; you know OD/ID, tnom, corrosion allowance, and code allowable stress basis.
16) Do you have maintenance + operating history relevant to damage (impact event, prior repairs, pressure/temperature history, corrosion environment)?
For example; you can confirm whether damage was a one-time impact vs repeated mechanical abuse.
17) For dents: have you measured maximum dent depth (pressurized and/or unpressurized) and documented the basis?
For example; dent depth measured at operating pressure, or conservatively use unpressurized depth when required.
18) For dents: have you measured spacing from the dent edge to the nearest weld joint and major structural discontinuity (and sketched it)?
For example; distance to a circumferential seam weld and distance to a nozzle or shell transition is recorded.
19) For gouges: have you sized the gouge geometry (depth/length/width/profile) using the Part 5 groove sizing approach?
For example; UT grid or profile method to define the gouge depth and shape for assessment inputs.
20) For gouges: do you have evidence the material toughness criterion for using Part 5 Level 1/2 is met (e.g., expected/known CVN ≥ 40 J at minimum operating temperature) OR the gouge has been dressed to remove work-hardened layer and sharp defects?
For example; grinding/blending to remove cold-worked layer after gouging, leaving a smooth profile.
21) For dent-gouge: do you have dent depth, gouge depth, material strengths (SMYS/UTS), pressure cycle info (if cyclic), and spacing to welds/discontinuities?
For example; ddp, dg, Pmax/Pmin, and distances to welds/nozzles are all documented.
22) For dent-gouge: do you have the Charpy/transition temperature basis used by Part 12 (e.g., CVN (including 2/3 sub-size handling if applicable) and the temperature corresponding to 40 J / 30 ft-lb, or a justified estimate)?
For example; you have lab CVN data or a documented estimate method tied to exemption curves.

D) Level 1 Screening (What Level 1 “expects” you to confirm)

23) Dent Level 1: Is the component non-cyclic (per your answer in Q14) so Level 1 dent screening is allowed?
For example; one-time start-ups per year and stable pressure most of the time → likely non-cyclic.
24) Dent Level 1: Have you identified the minimum operating metal temperature relevant to dent acceptability decisions?
For example; winter operation, depressurization, or start-up conditions that set minimum metal temperature.
25) Dent Level 1: Does the dent appear stable (no signs of tearing, cracking, or severe sharp kinking that would invalidate shell-theory assumptions)?
For example; sharp crease with suspected microcracking at the crease line → do not stop at Level 1.
26) Gouge Level 1: At minimum operating temperature, is toughness acceptable (CVN ≥ 40 J) OR was the gouge dressed to remove work-hardened layer so Level 1 may proceed to Part 5 evaluation?
For example; after blending/grinding, no sharp notches remain and surface is smooth.
27) Dent-Gouge Level 1: Have you determined the wall thickness used in the evaluation (including local loss region vs nominal basis) and the remaining thickness ratio concept used by Part 12?
For example; use measured minimum thickness at the gouge base and account for FCA when defining remaining thickness ratio.
28) Dent-Gouge Level 1: Do minimum thickness / length limit checks that gate Level 1 appear satisfiable for your component type (piping vs pressure vessel rules differ)?
For example; very thin remaining ligament after FCA → fails the gating check → Level 1 not satisfied.
29) Dent-Gouge Level 1: Does your dent depth and gouge depth combination fall in the “acceptable” region of the Part 12 dent-gouge interaction concept (ddp/Do vs dg/tc)?
For example; shallow dent with small gouge depth is usually acceptable; deeper dent + deeper gouge trends unacceptable.
30) Level 1 outcome readiness: If Level 1 is not satisfied, are you prepared to move to Level 2 / Level 3, rerate, repair, replace, or retire per the Part 12 decision flow?
For example; you already have a plan to obtain additional data for Level 2 or to install a temporary clamp/repair.

E) Level 2 Readiness (When cyclic service or when Level 1 is too conservative)

31) If the component is in cyclic pressure service, have you defined representative Pmax and Pmin (or a bounded cycle definition) for Level 2 inputs?
For example; daily pressure cycle from 50 psi to 250 psi during batch operations.
32) For gouges in Level 2, are you ready to evaluate the gouge using Part 5 Level 2 (since Part 12 points gouge acceptability back to Part 5 when toughness screening is met)?
For example; you have enough thickness profile data to run Part 5 Level 2 calculations.
33) For dent-gouge in Level 2, do you have the additional toughness/Charpy basis needed for the Level 2 RSF-type evaluation pathway?
For example; you can justify CVN input (full size or 2/3 subsize conversion basis) and related temperature basis.
34) If Level 2 is not satisfied, are you prepared to consider the Part 12 options: rerate, repair/replace, adjust FCA via remediation methods, or proceed to Level 3?
For example; reduce operating pressure/temperature until acceptable, or install engineered reinforcement.

F) Level 3 Triggers & Planning (Detailed analysis when Level 1/2 don’t apply)

35) Do any Level 3 “triggers” exist (geometry outside bounds, supplemental/thermal loads, closely spaced damage, non-longitudinal gouge in dent-gouge, complex cycles, creep-range concerns, etc.)?
For example; dent near a nozzle with significant piping loads → Level 3 stress analysis expected.
36) For Level 3, can you model the damage realistically using material + geometric nonlinearity (pressure stiffening / rerounding effects) rather than only linear elastic shell theory?
For example; FE model includes re-rounding of a dent under pressure so stresses aren’t over/under-estimated.
37) If a sharp kink/bend exists, can you use a continuum/solid model (not shell theory) to capture the stress state accurately?
For example; a tight crease in a dent is better treated with solid elements to capture local bending and strain.
38) Have you identified the relevant failure modes for Level 3 (plastic collapse/local failure/buckling/fatigue/ratcheting/creep; and crack stability if toughness is insufficient)?
For example; if toughness is uncertain, evaluate gouge as crack-like flaw using Part 9 concepts where applicable.

G) Remaining Life, Remediation, Monitoring, Documentation

39) Remaining life: is there any reason remaining life must be evaluated (corrosive environment uncertainty, cyclic history uncertainty, or creep-range operation)?
For example; you cannot bound future corrosion allowance near the damage → consider monitoring or deeper analysis.
40) Remediation planning: do you agree dents/dent-gouges are potentially severe because local ductility/strength at max deformation is hard to prove, so repair/replacement is often recommended unless condition is adequately evaluated?
For example; if you cannot justify local material condition, you may choose engineered repair rather than “calculate-only”.
41) If reinforcement is selected, will it be designed using the original construction code principles (e.g., stiffening plates/lap patches, controlled re-rounding methods)?
For example; engineered lap patch sized by code allowable stresses, with proper QA and inspection hold points.
42) If corrosion/metal loss exists near the damage, will you consider general corrosion remediation methods (and special filling/lining considerations for deep localized loss)?
For example; fill deep pits with suitable material before lining so the lining does not bridge voids.
43) In-service monitoring: if monitoring is warranted, will you plan periodic visual checks and repeatable field measurements of distortion (consistent method/locations)?
For example; record dent depth reference points and re-measure every turnaround to detect growth/relaxation.
44) Documentation: will you include all inspection data/field measurements and keep a sketch/photo showing location and orientation of the damage?
For example; a photo with tape scale + a sketch marking clock position and distance from circumferential seam weld.

When to Use API 579 Part 12

API 579 Part 12 is typically used when the controlling condition is mechanical damage and the decision depends on geometry and remaining section at the damaged location. Common triggers include:

  • Dents from impact, handling, lifting, or contact damage on vessels, piping, or tank components
  • Gouges or surface cuts that reduce local thickness or create stress concentration
  • Combined dent-gouge damage where deformation and section loss interact
  • Damage located near welds/nozzles/attachments or other discontinuities where local stress is elevated
  • A need to decide whether the equipment can continue operating as-is, needs restrictions, or requires repair now versus at turnaround

If inspection indicates a crack-like flaw associated with the damage, a Part 9 evaluation may also be required for flaw acceptability.

What to Gather if Screening Indicates FFS Is Needed

If this workflow indicates that a formal API 579 Part 12 assessment is recommended, prepare the following to support a defensible evaluation:

  • Dent geometry measurements (depth, diameter/extent, shape profile if available, and orientation)
  • Gouge dimensions (length, width, depth, radius/sharpness, and remaining thickness at the gouge)
  • Location details (distance to welds/nozzles/attachments and whether damage is on internal or external surface)
  • Component geometry and thickness (nominal thickness and local thickness readings)
  • Operating basis (pressure, temperature, and whether service is cyclic or vibration-prone)
  • Photos and inspection documentation confirming the damaged region and measurement method

Request an API 579 Part 12 Dent and Gouge Assessment

If this workflow indicates that an API 579 Part 12 Dent and Gouge Fitness-for-Service (FFS) assessment is needed, the next step is a decision-ready engineering evaluation based on your damage measurements, inspection findings, and operating envelope.

Inspection 4 Industry LLC (I4I) performs API 579-1 / ASME FFS-1 Part 12 assessments and delivers a complete report package that operations can act on: fit-for-service or not fit-for-service at the evaluated conditions, any required operating restrictions or rerated limits, and clear integrity actions—repair now, repair at turnaround, or monitor with a defined inspection plan.

To proceed, send photos, dent depth/shape measurements, gouge dimensions (length/width/depth), local thickness readings, and the operating basis, and request an API 579 Part 12 Dent and Gouge Assessment (FFS).

 

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