API 579 Fitness for Service Assessment (FFS) Services

At Inspection 4 Industry LLC (I4I), we perform API 579 Fitness for Service Assessment evaluations in accordance with API 579-1 / ASME FFS-1 and deliver a complete engineering report suitable for integrity decisions, operating limits, repair planning, and management review.

API 579 Fitness for Service Assessment (FFS) is one of the fastest ways to turn inspection findings into a clear engineering decision—can the equipment remain in service, does it need rerating, or should it be repaired now or at the next turnaround.

If you have an active inspection finding and want a quick, structured screen, use the interactive workflows on this page to determine whether an API 579 Fitness for Service Assessment (FFS) is recommended for your equipment based on the observed damage condition.

These FFS screening workflows align with common API 579 damage mechanisms, including general metal loss, local metal loss, pitting corrosion, crack-like flaws, hydrogen damage (HIC/SOHIC/blistering), weld misalignment and shell distortion, dents and gouges, creep damage, fire damage, laminations, and fatigue.

API 579 Fitness for Service Assessment (FFS) Deliverables

An API 579 Fitness for Service Assessment (FFS) is intended to end with one outcome: a clear, defensible operating decision supported by traceable inputs and a documented engineering basis. In practice, an FFS report is written so integrity, operations, and management can understand what was evaluated, what assumptions were used, and what limits or actions control safe operation.

At a high level, a complete API 579 Fitness for Service Assessment (FFS) report typically includes:

Assessment scope mapped to API 579: the applicable Part(s) and the assessment Level used (Level 1 / Level 2 / Level 3)
Bottom-line decision at the evaluated conditions: fit for service or not fit for service
Operating limits when required: pressure/temperature limits and any necessary restrictions to remain within an acceptable envelope
Recommended integrity actions: repair now, repair at turnaround, or monitor/operate with defined requirements
Inspection and monitoring basis: suggested intervals, methods, and targets tied to the controlling damage mechanism
Traceable engineering basis: inputs, assumptions, calculations, and a structured format suitable for internal review and audits

What to Provide to Start an API 579 FFS

Before starting an API 579 Fitness for Service Assessment (FFS), gather the information below so the screening and evaluation are based on complete, traceable inputs.

Inspection/NDE reports and thickness/scan data (as applicable)
Equipment ID, service, and component location
Operating pressure/temperature (normal and upset if relevant)
Available drawings or key dimensions (thickness, diameter, weld/nozzle locations)
Damage photos and location marking (where applicable)
Target run length to next outage / decision deadline

API 579 Fitness for Service Assessment (FFS) Part 3 - Brittle Fracture

API 579 Fitness for Service Assessment (FFS) Part 3 Brittle Fracture Assessment is used when low metal temperature, high stress, and flaw sensitivity combine to create a sudden fracture risk. This is not a corrosion-rate problem—it’s a fracture mechanics / toughness problem driven by metal temperature excursions, material notch toughness, weld details, and crack-like flaws.

This screening is commonly used to support restart and continued-operation decisions after winter operation, startup/shutdown, upset cooling, or unexpected depressurization. If the equipment may experience low metal temperatures near its toughness limits, Part 3 helps determine acceptability and whether operating restrictions, rerating, repairs, or additional inspection are required.

A common example is a light-ends receiver or cold-side exchanger channel experiencing a metal temperature drop below the expected operating envelope during a winter event. In these cases, the site needs a decision that can stand up to technical scrutiny. We evaluate using the available design basis, operating envelope, and inspection findings and issue a report stating whether the component is acceptable at the evaluated conditions or if limits are needed.

Start the Part 3 Brittle Fracture Screening

API 579 Fitness for Service Assessment (FFS) Part 4 - General Metal Loss

API 579 Fitness for Service Assessment (FFS) Part 4 General Metal Loss Assessment is used when wall loss is broad and widespread (not a single isolated pit or local thin spot). This is common in refineries and process plants where long-term corrosion or erosion causes overall thinning, and the key question becomes: does the remaining thickness support continued operation at current conditions, or is rerating required?

API 579 Part 4 general metal loss assessments are performed using your thickness data (UT grids, C-scan mapping, or inspection point readings) and your operating basis. The assessment determines acceptability for continued service and, when needed, establishes rerated limits so the equipment can operate safely to the next planned outage.

A common example is a vacuum column bottom section with widespread thinning across a large shell area after years of high-severity service. Operations and management need a defensible decision: keep running to turnaround, rerate, or repair now. Part 4 provides that decision with clear engineering justification.

Start the Part 4 General Metal Loss Screening

API 579 Fitness for Service Assessment (FFS) Part 5 - Local Metal Loss

API 579 Fitness for Service Assessment (FFS) Part 5 Local Metal Loss Assessment applies when average thickness can look acceptable, but a localized thin area (LTA) or groove-like feature controls integrity. This is common when corrosion is concentrated—under deposits, at nozzles, near welds, or at geometric discontinuities—where a small region drives the run/repair/rerate decision.

API 579 Part 5 local metal loss assessments are performed using detailed thickness profiles from UT mapping, grid readings, or scans to properly define the local region and evaluate remaining strength. The result is a clear decision on whether the component is fit for continued service at the evaluated conditions and whether rerated limits or restrictions are required.

A refinery example is localized under-deposit corrosion in a crude overhead circuit producing a concentrated low-thickness region near a nozzle or discontinuity. The key question becomes: can it safely operate until the next shutdown, and under what operating limits? We characterize the local feature correctly, apply the Part 5 acceptance checks, and issue a report stating fit / not fit, any rerated limits, and whether repair is immediate or can be planned for turnaround with monitoring.

Start the Part 5 Local Metal Loss Screening

API 579 Fitness for Service Assessment (FFS) Part 6 - Pitting Corrosion

API 579 Fitness for Service Assessment (FFS) Part 6 Pitting Corrosion Assessment is used when corrosion is concentrated into pits rather than uniform thinning. Pitting is not “just thinning”—a small number of deep pits can control integrity even when average thickness looks acceptable. Part 6 addresses both localized pitting and widespread pitting, including cases where active pitting must be evaluated against a future inspection date.

API 579 Part 6 pitting corrosion assessments are performed using your inspection data to determine whether the equipment is acceptable for continued service at the evaluated conditions and whether it will remain acceptable to the next planned inspection. This provides a clear basis for decisions such as continue operating, rerate, repair, or increase monitoring.

A common oil & gas example is a cooling-water exchanger channel head (water box) with scattered but deep pits. The site needs more than “watch it.” We evaluate pit severity using the Part 6 methodology and issue a report that answers two key questions: Is it acceptable now? and Will it remain acceptable until the next planned inspection?—along with a monitoring interval aligned to the risk.

Start the Part 6 Pitting Corrosion Screening

API 579 Fitness for Service Assessment (FFS) Part 7 - Hydrogen Damage

API 579 Fitness for Service Assessment (FFS) Part 7 Hydrogen Blistering, HIC, and SOHIC Assessment is used when hydrogen damage indications are present and integrity cannot be judged by thickness averages alone. Hydrogen damage can drive overly conservative decisions if it’s not evaluated correctly—especially when indications are near welds, discontinuities, or form arrays that may interact. Part 7 provides a structured method to evaluate hydrogen blistering, HIC (Hydrogen-Induced Cracking), and SOHIC (Stress-Oriented Hydrogen-Induced Cracking) and determine whether continued operation is acceptable.

API 579 Part 7 hydrogen damage assessments are performed using your UT data and inspection findings to characterize the damage, select the correct assessment route, and link to other API 579 Parts when required. The result is a clear decision supported by a documented engineering basis—fit / not fit, operating limits when needed, and an inspection plan tied to the hydrogen damage mechanism.

A realistic refinery scenario is a sour water stripper drum or hydrotreating circuit where UT scanning identifies HIC-type indications near a weld and blister-like features in a localized region. Operations needs to know if the equipment can safely run to the next turnaround and what monitoring is necessary. We execute the Part 7 pathway and deliver a report stating acceptability, any required rerating or repair actions, and a monitoring plan aligned to hydrogen damage.

Start the Part 7 Hydrogen Damage Screening

API 579 Fitness for Service Assessment (FFS) Part 8 - Weld Misalignment

API 579 Fitness for Service Assessment (FFS) Part 8 Weld Misalignment and Shell Distortions Assessment applies when geometry—not wall loss—controls integrity. Conditions like settlement, out-of-roundness (ovality), bulges, peaking, and weld misalignment can create high local stresses and instability risk even when thickness readings look acceptable. Part 8 provides the method to determine whether the observed distortion is acceptable for continued pressurized service.

API 579 Part 8 distortion and misalignment assessments are performed using dimensional survey data, targeted measurements, and operating conditions to evaluate acceptability and define required actions. The outcome is a clear engineering decision—fit / not fit, whether rerating is required, and whether correction, reinforcement, or monitoring is needed.

A common refinery scenario is a tall fractionation column that develops measurable ovality from foundation movement, or a localized bulge after an internal event. You provide the dimensional data; we apply Part 8 checks and issue a report stating whether the distortion is acceptable at current operating conditions, whether operating limits are needed, and whether correction can be planned for the next outage or must be executed immediately.

Start the Part 8 Weld Misalignment & Shell Distortion Screening

API 579 Fitness for Service Assessment (FFS) Part 9 - Crack-Like Flaws

API 579 Fitness for Service Assessment (FFS) Part 9 Crack-Like Flaw Assessment is used when inspection finds planar indications or flaw shapes that must be treated as crack-like to confirm safe operation. Cracks require a different approach than metal loss because integrity is controlled by fracture mechanics, stress intensity, and crack growth potential—not remaining thickness averages.

API 579 Part 9 crack-like flaw assessments are performed when PAUT, TOFD, MT/PT follow-up, or other NDE indicates crack-like features in pressure equipment. Using the available inspection sizing, stresses, material data, and operating conditions, the assessment determines whether the component is acceptable at current service or whether operating limits, rerating, repair, or monitoring are required.

A typical refinery example is a crack-like indication identified by PAUT or TOFD at a nozzle-to-shell weld on an FCC main fractionator, or a weld in an amine circuit with stress concentration and cyclic operation. The site needs a decision: can it run safely to the next planned shutdown, or is immediate repair required? We execute the Part 9 assessment at the applicable Level and issue a report stating fit / not fit, any required operating limitations, and the recommended integrity action and timing.

Start the Part 9 Crack-Like Flaw Screening

API 579 Fitness for Service Assessment (FFS) Part 10 - Creep Assessment

API 579 Fitness for Service Assessment (FFS) Part 10 Creep Assessment is used when equipment operates in the creep temperature range and damage becomes a time-dependent remaining-life problem. Unlike corrosion, creep is driven by sustained temperature and stress over long periods, and integrity decisions depend on whether the component has sufficient remaining life to safely meet the next run length.

API 579 Part 10 creep and remaining-life evaluations for high-temperature pressure equipment are performed to determine acceptability for continued service and to establish practical run/repair planning. Using your operating history, temperatures, stresses, and inspection findings, the evaluation assesses creep damage and defines whether continued operation is acceptable, whether rerating or operating limits are required, and what monitoring or inspection interval supports safe operation.

A classic refinery scenario is fired heater outlet piping, hot headers, or high-temperature piping circuits with long-term exposure at elevated temperature—sometimes combined with operational cycling. The business decision is whether the circuit can safely reach the next planned outage and what inspection scope is needed. We execute the Part 10 methodology and deliver a report that supports a practical integrity plan: continue with defined monitoring, rerate to manage remaining life, or schedule repair/replacement at a defined outage to prevent a run-ending failure.

Start the Part 10 Creep Screening

API 579 Fitness for Service Assessment (FFS) Part 11 - Fire Damage

API 579 Fitness for Service Assessment (FFS) Part 11 Fire Damage Assessment is used when equipment has been exposed to fire, flame impingement, or overheating and the site needs an urgent, defensible restart decision. Fire damage is not only “how hot did it get”—it can involve distortion, loss of strength/toughness, metallurgical property degradation, and changes that affect safe operation under pressure.

I API 579 Part 11 fire damage evaluations for pressure vessels, piping, and tanks exposed during incidents such as pool fires, jet fires, or localized seal fires are performed to support restart decisions. Using event information and inspection results, the evaluation determines whether affected components can safely return to service as-is, require rerating/operating restrictions, or require repair or replacement before restart.

A common scenario is a pump seal fire or localized hydrocarbon pool fire that heats nearby piping or a small vessel such as an overhead accumulator or separator. The plant needs a defensible answer before startup. You provide the event description, exposure area information, and inspection results (dimensional checks, NDE findings, hardness/metallurgical checks if performed). We execute the Part 11 assessment route and issue a report stating whether the equipment is acceptable at the evaluated conditions and what actions are required for safe restart.

Start the Part 11 Fire Damage Screening

API 579 Fitness for Service Assessment (FFS) Part 12 - Dents & Gouges

API 579 Fitness for Service Assessment (FFS) Part 12 Dents, Gouges, and Dent-Gouge Combination Assessment is used when mechanical damage affects pressure equipment and the integrity question is controlled by geometry and local strain, not corrosion rate. Dents, gouges, and combined dent-gouge damage can introduce high local stress, loss of section, and fatigue sensitivity, especially in cyclic service or near welds and nozzles.

API 579 Part 12 mechanical damage assessments are performed to determine whether the damaged area is acceptable for continued pressure service and whether additional evaluation is required for fatigue or crack initiation risk. Using your measurements (dent depth/shape, gouge dimensions, remaining thickness, and location details), the Part 12 methodology is applied to provide a clear operating decision.

A common oil & gas scenario is a gas plant separator or produced-water vessel dented during maintenance, lifting, or an unexpected impact, with visible surface damage in the affected region. The operator needs a clear decision: keep running to shutdown, repair now, rerate, or monitor. We characterize the damage geometry, execute the Part 12 assessment approach, and issue a report stating acceptability, any required operating limitations, and repair timing recommendations aligned to the result.

Start the Part 12 Dent & Gouge Screening

API 579 Fitness for Service Assessment (FFS) Part 13 - Laminations

API 579 Fitness for Service Assessment (FFS) Part 13 Laminations Assessment is used when UT scanning identifies laminations, planar separations, or embedded discontinuities in plate material that may affect structural integrity. Laminations can appear during UT mapping even after years of operation, and the integrity concern depends on size, location, orientation, proximity to welds/seams/nozzles, and whether the lamination could interact with service stresses or behave like another damage type.

API 579 Part 13 lamination evaluations are performed to determine whether reported laminations are acceptable for continued service and whether additional actions are required. The Part 13 routing logic is applied and linked to other API 579 Parts when needed (for example, when a lamination acts like a crack-like feature or affects local strength near discontinuities).

A common refinery scenario is UT scanning on a vessel shell course—such as a desalter vessel or a drum in corrosive service—where laminations are reported near a seam and close to weld areas. The site needs a clear decision on whether they threaten integrity, require monitoring, or justify repair planning. We execute the Part 13 assessment approach and issue a report stating acceptability, any monitoring requirements, and whether repair or replacement planning is recommended based on the evaluated condition.

Start the Part 13 Lamination Screening

API 579 Fitness for Service Assessment (FFS) Part 14 - Fatigue Damage

API 579 Fitness for Service Assessment (FFS) Part 14 Fatigue Damage and Ratcheting Assessment is used when equipment integrity is controlled by cyclic loading rather than corrosion alone. Fatigue and ratcheting are driven by repeated cycles such as startups/shutdowns, pressure and temperature swings, thermal transients, vibration-induced cycling, and other operational fluctuations. When cracking is present near welds or attachments—or when cycling history is significant—Part 14 helps determine remaining life and safe operating limits.

API 579 Part 14 fatigue and ratcheting evaluations are performed to convert operating cycles into a clear integrity decision. Using available plant data and operating history, the loading and cycle basis is developed, fatigue usage and ratcheting risk are evaluated at the applicable assessment Level, and it is determined whether the component is acceptable for continued service or whether operating changes, cycle limits, monitoring, repair, or replacement are required.

A common refinery scenario is a compressor discharge circuit or overhead system with frequent start-stop operation and thermal swings, where cracking develops near weld toes, attachments, or discontinuities. The site needs a defensible answer: can it safely continue under the current operating pattern, do cycle limits or operational changes apply, or must repair be completed now? We execute the Part 14 assessment route and issue a report stating acceptability, any required operating restrictions, and recommended integrity actions tied to the evaluated fatigue risk.

Start the Part 14 Fatigue Screening

When More than One API 579 Part Applies

Real equipment rarely has only one damage mechanism. A single circuit can show general metal loss, local metal loss, and pitting at the same time. Sour service can combine hydrogen damage (HIC/SOHIC/blistering) with crack-like indications. After a fire event (Part 11), the controlling condition may still be metal loss, cracking, distortion, or creep—and the correct decision depends on identifying the controlling damage mechanism and the controlling operating limit.

An API 579 Fitness for Service Assessment (FFS) is most effective when the evaluation is integrated across all applicable Parts and Levels so the results are consistent and not unnecessarily conservative. The case is routed to the correct API 579 Part(s), the appropriate assessment Level is applied, and one coherent conclusion is produced that tells your team what matters most: whether the equipment is fit for service at the evaluated conditions and what limits/actions control safe operation.

Start Your API 579 Fitness for Service Assessment (FFS)

If you have an inspection finding and need a defensible decision, request an API 579 Fitness for Service Assessment (FFS) from Inspection 4 Industry LLC. Send your inspection/NDE results and operating basis, and we will evaluate the applicable Part(s) and issue a decision-ready report with fit-for-service or not fit-for-service conclusions, rerated limits (if needed), and clear integrity actions to support continued safe operation.

How to Choose the Correct Part

How to Choose the Correct API 579 Part

Low-temperature brittle fracture limits (MAT/CET, pressure–temperature basis) → Part 3
Widespread thinning across a large area → Part 4
Localized thin area (LTA) or groove-like corrosion/erosion → Part 5
Pitting corrosion where pit depth/severity controls integrity → Part 6
Hydrogen damage (blistering, HIC, SOHIC) → Part 7
Misalignment, peaking, ovality, bulging, or shell distortion → Part 8
Crack-like flaw acceptability (planar flaw-focused) → Part 9
High-temperature creep / remaining life → Part 10
Fire or overheating exposure / restart decision → Part 11
Mechanical damage (dents, gouges, dent-gouge) → Part 12
Laminations / embedded planar discontinuities → Part 13
Cyclic loading (fatigue, ratcheting) → Part 14

API 579 Fitness for Service Assessment (FFS) FAQ

What is an API 579 Fitness for Service Assessment (FFS)?
An API 579 FFS is an engineering assessment used to determine whether equipment with damage or flaws can remain safely in service at defined operating conditions.

What information do I need to start an FFS?
Typically: inspection/NDE results, equipment details (material/thickness), operating pressure/temperature, and the damage location and extent.

What is the difference between Level 1, Level 2, and Level 3?
Level 1 is conservative screening, Level 2 is more detailed using better inputs, and Level 3 is the highest rigor for complex conditions and may require advanced analysis.

Which Part should I use if I have multiple damage mechanisms?
Use the workflow that matches the controlling condition, or request an integrated assessment so one report identifies the controlling risk and operating limit.

If the screening indicates concern, what’s next?
Request a formal API 579-1 / ASME FFS-1 assessment for the applicable Part and Level to issue a fit/not-fit decision, limits (if needed), and integrity actions.