API 579 Part 9 Crack Like Flaws Assessment Screening

API 579 Part 9 Crack Like Flaws Assessment is used when inspection identifies planar indications or flaw shapes that must be treated as crack-like to confirm safe operation. Unlike metal loss, crack-like flaws are evaluated using fracture mechanics concepts because integrity is controlled by flaw size, stress level, material properties, and service conditions—not by thickness averages alone.

Use this screening workflow to confirm Part 9 applicability and whether you have the inspection/NDE basis needed to support a defensible evaluation. In many cases, a credible Part 9 assessment requires reliable flaw sizing (length, depth, and orientation), correct flaw location definition (weld/HAZ/base metal/nozzle region), and a clear operating basis to support the acceptability decision.

Use the screening questions below to determine whether a formal Part 9 evaluation is recommended.

API 579 Part 9 — Crack-Like Flaws Assessment Screening (Workflow)

Instruction: Answer all questions (Yes / No / N/A), then click “Check if FFS is needed”.

Note: If an item truly does not apply to your equipment or scenario, select N/A.

1) Has inspection identified a crack-like flaw (planar flaw predominantly characterized by length and depth, with a sharp root radius), such as a planar crack, lack of fusion/lack of penetration in a weld, or a sharp groove-like localized feature that behaves like a crack?
For example; PAUT on a nozzle-to-shell weld reports a planar indication 2.0 in long × 0.18 in deep in a 0.75 in wall.
2) Is the indication volumetric but should be treated as crack-like (conservative) because micro-cracking cannot be ruled out by the available NDE?
For example; UT shows aligned inclusions/porosity along a weld root for 1.5 in, and you conservatively treat it as crack-like.
3) Is the component operating in the creep range (high-temperature regime where creep damage/cracking rules apply)?
For example; a hot outlet header operates near 900°F for long periods (creep-range), so Part 10 may govern and Part 9 Level 1/2 are not applicable.
4) Are dynamic loading effects significant at the flaw location (e.g., earthquake, impact, water hammer, severe transient events)?
For example; repeated water-hammer events occur at a restraint near the crack location, making dynamic effects significant.
5) Is the flaw subject to loading conditions and/or a service environment that may result in crack growth in service?
For example; environmental cracking is suspected and the crack may grow between inspections, pushing you toward Level 3 + remaining life steps.
6) Are you eligible to use Level 1 / Level 2 (not creep-range, no significant dynamic loading, and crack growth not expected for Level 1/2 screening intent)?
For example; if crack growth is expected, you generally route to Level 3 + remaining life evaluation rather than Level 1/2.
7) If you intend Level 1: is the component geometry eligible (flat plate, cylinder, or sphere) and within Level 1 geometric limits?
For example; a thin-wall cylindrical shell section away from discontinuities is eligible, but complex geometry may not be.
8) If you intend Level 1: is the wall thickness at the flaw location within the Level 1 thickness limitation?
For example; if thickness exceeds the Level 1 limit, you typically move to Level 2 or Level 3.
9) If you intend Level 1: is the flaw type permitted (surface or through-wall) and within Level 1 size limits (including maximum permitted crack length for the selected configuration)?
For example; a surface flaw under the Level 1 maximum length limit may qualify; a very long crack may not.
10) If you intend Level 1: is the flaw orientation appropriate for the Level 1 case (or conservatively re-characterized to an equivalent orientation relative to the principal stress direction)?
For example; if a crack is skewed, you re-characterize it to an equivalent conservative crack aligned with the governing stress direction.
11) If you intend Level 1: is the flaw sufficiently far from a major structural discontinuity (spacing requirement)?
For example; the crack is far enough from nozzles/knuckles/supports that discontinuity effects are not governing in Level 1 screening.
12) Do you have original equipment design data sufficient to define the assessment basis (pressure/temperature, dimensions, nominal thickness, joint details)?
For example; design P/T, ID/OD, nominal thickness, weld joint type, and geometry at the flaw location are available.
13) Do you have maintenance & operating history sufficient to define the assessment case (repairs, PWHT status, pressure tests, upsets, changes in operating envelope)?
For example; you know if it was repaired, whether it was PWHT’d, and whether it had a pressure test after repair.
14) Are loads and stresses available or can they be determined at the flaw location for the governing operating condition(s) (pressure + supplemental loads, thermal stresses where applicable)?
For example; you can determine membrane + bending (and any secondary/peak where needed) at the crack location.
15) Have you defined the governing load cases and (if crack growth is possible) the number/magnitude of cycles needed for crack-growth evaluation?
For example; pressure cycles, thermal start/stop cycles, and any repeated external loading are documented as a basis for remaining life.
16) Are required material properties available for the selected assessment path (strength and fracture toughness basis, including weld/HAZ where applicable)?
For example; base metal grade is known and toughness basis is supported by testing or an approved estimation approach, with PWHT status documented.
17) Has the flaw been characterized (length, depth, type: surface/embedded/through-wall; orientation; location), including identifying a governing flaw if multiple/branched cracks exist?
For example; multiple branched cracks exist, but you identify the predominant crack (or you route to advanced methods if you cannot).
18) Is the flaw in an inspectable region with sufficient sizing reliability, or have you conservatively addressed any uninspectable area adjacent to the flaw?
For example; behind a pad/obstruction you cannot fully inspect, so you postulate a conservative crack size for the uninspectable ligament.
19) Have stresses at the flaw location been classified appropriately (primary, secondary, residual) for your chosen method (Level 2 FAD and/or Level 3 numerical)?
For example; pressure membrane is primary; thermal gradient may be secondary; weld residual stress may require special treatment.
20) Is weld residual stress potentially significant for crack driving force at this location (welded joint, repair weld, high restraint), requiring inclusion in the assessment basis?
For example; a non-PWHT repair weld at a high-restraint nozzle corner may be residual-stress dominated for crack driving force.
21) If residual stress is included: have you accounted for factors that change residual stress assumptions (PWHT, pressure test after weld/repair, original vs repair weld, and proximity to the weld centerline)?
For example; a pressure test after repair may reduce effective residual stress assumptions compared to an as-welded condition.
22) Have you selected the intended assessment level (Level 1, Level 2, or Level 3) consistent with applicability and complexity (discontinuity effects, stress determination needs, and crack growth expectations)?
For example; a crack at/near a major discontinuity usually routes to Level 2 or Level 3 rather than Level 1 screening.
23) If Level 2: are you prepared to perform an FAD-based assessment (driving force + plastic collapse check) using a defensible toughness basis?
For example; you will compute the assessment point and judge whether it falls inside/on the acceptance boundary.
24) If Level 3: will you explicitly model the crack or otherwise use an accepted numerical fracture approach (e.g., J-integral / crack front driving force) suitable for plasticity and complex geometry?
For example; you include crack-front evaluation in the model and ensure the model addresses both fracture and plastic collapse under governing loads.
25) Is your objective to determine a Minimum Allowable Temperature (MAT) or pressure–temperature envelope for brittle fracture resistance using a fracture-mechanics approach consistent with Part 9 options?
For example; cold start-up decision requires MAT based on stress state and flaw basis.
26) If using a simplified MAT option: do you meet the stated limitations for that simplified approach (material class and loading/geometry restrictions, and other stated limits)?
For example; pressure-governed loading and qualifying material/thickness conditions allow simplified MAT; otherwise use the more general route.
27) If hydrogen service is relevant: have you accounted for hydrogen-related effects required by the Part 9 MAT/assessment provisions before finalizing acceptability?
For example; you consider hydrogen effects when establishing toughness/MAT decisions for susceptible services.
28) If crack growth is possible/expected: do you have the inputs needed to perform remaining life (crack growth) calculations (cycles/histogram, operating transients, and an approved crack growth model/data basis)?
For example; you document pressure/temperature cycles and use a crack growth approach to estimate time/cycles to reach a limiting flaw size.
29) If considering leak-before-break (LBB): can you evaluate through-wall crack conditions and confirm leak detection/monitoring capability supports the intended acceptance basis?
For example; you confirm that leakage would be detected reliably before unstable fracture could occur for the postulated through-wall flaw.
30) If acceptability is not demonstrated (or uncertainty is high): have you identified a remediation path (remove/repair crack, reduce driving force, increase toughness, change process/environment, etc.)?
For example; repair weld, remove flaw by grinding + re-inspect, revise start-up procedures, or adjust chemistry to reduce crack growth tendency.
31) If continued operation relies on monitoring: have you defined an in-service monitoring / re-inspection plan capable of trending flaw size and supporting the assumed growth model?
For example; you set inspection interval and technique (PAUT/TOFD) with demonstrated sizing repeatability for depth growth trending.
32) Have you documented the basis for the governing flaw selection, assumptions, and uncertainties (sizing tolerance, stress determination, residual stress treatment, and toughness basis) for auditability?
For example; you record UT sizing tolerance, stress method, any residual stress bounding assumptions, and the toughness source/basis used.
33) If the flaw is in/near weld metal or HAZ: have you confirmed the assessment uses the controlling (lowest) toughness zone (base/weld/HAZ) consistent with your documentation?
For example; the HAZ is the controlling region, so toughness basis is not taken from base metal if HAZ governs.
34) Have you confirmed the assessment considers the governing operating condition(s) (worst-case P/T, transients, and load combinations) for crack driving force?
For example; highest primary stress case governs fracture; another transient may govern secondary stress contribution; both are checked.
35) Are you prepared to produce the final Part 9 deliverables (acceptability statement, level used, inputs/assumptions, governing flaw, monitoring/remediation plan if needed) consistent with Part 9 documentation expectations?
For example; final report includes acceptability decision, assessment level, key inputs, and next inspection/remediation actions.
Answer all questions, then click “Check if FFS is needed”.

When to Use API 579 Part 9

API 579 Part 9 is typically used when the controlling concern is a crack-like flaw acceptability decision. Common triggers include:

  • PAUT, TOFD, MT/PT follow-up, or other NDE identifies planar indications that must be evaluated as crack-like flaws
  • Flaws are located at welds, HAZ, seam welds, nozzle-to-shell welds, attachments, or other high-stress regions
  • A decision is needed on continued operation at the evaluated conditions versus repair before restart or before the next outage
  • The case requires defining acceptability using flaw size, stresses, and material resistance to crack extension
  • The integrity plan depends on whether the flaw is acceptable as-is, requires monitoring, or requires repair/replacement

If the primary concern is low-temperature brittle fracture limits (MAT/CET or pressure–temperature basis), route the evaluation to API 579 Part 3. If the controlling condition is hydrogen damage morphology, consider Part 7 in addition to Part 9 when applicable.

What to Gather if Screening Indicates FFS Is Needed

If this workflow indicates that a formal API 579 Part 9 crack like flaws assessment is recommended, prepare the following to support a defensible evaluation:

  • NDE reports and sizing results (flaw length, depth, through-wall position, orientation, and confidence/accuracy of sizing)
  • Flaw location details (weld/HAZ/base metal, nozzle region, seam weld, distance to discontinuities)
  • Equipment/component geometry (thickness, diameter, weld configuration, and drawings if available)
  • Operating basis (pressure, temperature, and any relevant transients or cyclic conditions)
  • Material properties and records if available (strength, toughness basis, PWHT status, and fabrication/repair history)
  • Planned run length and inspection strategy (re-inspection interval, method, and sizing requirements)

Request an API 579 Part 9 Crack Like Flaws Assessment (FFS)

If this workflow indicates that an API 579 Part 9 Crack Like Flaws Fitness-for-Service (FFS) assessment is needed, the next step is a decision-ready engineering evaluation using your inspection/NDE results, equipment details, and operating conditions.

Inspection 4 Industry LLC (I4I) performs API 579-1 / ASME FFS-1 Part 9 assessments of existing equipment for crack-like flaw acceptability and delivers a complete report stating fit-for-service or not fit-for-service, any required operating restrictions or rerated limits, and practical integrity actions—repair now, repair at turnaround, or monitor with defined re-inspection intervals aligned to the controlling flaw behavior.

To proceed, send your flaw sizing data (length, depth, orientation), inspection method results (PAUT/TOFD or equivalent), weld/location details, and your operating basis and request an API 579 Part 9 Crack Like Flaws Assessment (FFS).

 

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