API 579 FFS Level 1
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API 579 FFS Level 1 — General Metal Loss & LTA

Fitness-For-Service Screening per API 579-1 / ASME FFS-1 Parts 4 & 5

Level 1 FFS screening for corroded pressure equipment. Implements Part 4 (General Metal Loss) and Part 5 (Local Thin Area) of API 579-1/ASME FFS-1 for cylindrical shells under internal pressure. If Level 1 passes, the equipment is fit for continued service at MAWP. If Level 1 fails, escalate to Level 2.

Equipment

in
in
psig
psi
SA-516 Gr 70 @ ≤100°F = 17,500

Inspection Data

in
Thinnest point in CML / inspection area
in
Arithmetic average over CML
in
Corrosion rate × interval to next inspection
in
To nearest nozzle / weld / head

Local Thin Area (Part 5)

in
Longitudinal extent of thin region
in
in
Sound metal away from LTA

📚 Learn the Theory

FFS framework, Level 1 vs 2 vs 3, RSF derivation, LTA acceptance criteria, MAWP reduction.

Read Engineering Guide →

Key Equations

Required wall thickness (ASME VIII UG-27):

tmin = P · R / (S · E − 0.6 · P)

Future wall available:

tfuture = tmm − FCA

General-loss acceptance (Part 4):

tam − FCA ≥ tmin AND tmm − FCA ≥ max(0.5·tnom, 0.1·tnom + 0.1 in)

LTA shell parameter (Part 5):

λ = 1.285 · s / √(D · tmin)

Remaining Strength Factor:

RSF = (tmm − FCA) / tmin [acceptable RSF ≥ 0.9]

Reduced MAWP if RSF < RSFallow:

MAWPr = MAWP · (RSF / RSFallow)

Related Calculators

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B31G / Modified

Remaining strength for pipeline metal loss — companion FFS.
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MAOP / MAWP

Re-calc allowable pressure at reduced thickness.
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Class Location / HCA

FFS in HCA segments has tighter intervals.
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Material Selection

Allowable stress at temperature.