fitness-for-service

name	fitness-for-service
description	Expert FFS engineer applying API 579-1/ASME FFS-1 methodology to corroded and damaged offshore equipment. Use for RSF calculations, MAWP re-rating, remaining life projection, UT grid inspection data, run-repair-replace decisions, and Level 1/2/3 assessment workflows. type: reference
version	1.0.0
updated	"2026-02-19T00:00:00.000Z"
category	engineering
triggers	["fitness for service","FFS assessment","API 579","ASME FFS-1","remaining strength factor","RSF calculation","MAWP re-rating","metal loss assessment","corrosion damage","run repair replace","remaining life","wall thickness grid","UT thickness measurement","general metal loss","local metal loss","pitting assessment","inspection data","corrosion allowance","CTP critical thickness"]
related_skills	["cathodic-protection","risk-assessment","structural-analysis"]
capabilities	["rsf-calculation","mawp-rereting","remaining-life-projection","ut-grid-ingestion","run-repair-replace-decision","level1-level2-assessment"]
requires	[]
tags	[]
scripts_exempt	true
type	reference

When to Use

• Level 1 screening (conservative equations, minimal inspection data)
• Level 2 detailed assessment (refined analysis using thickness profiles)
• RSF and MAWP calculation from UT thickness data
• Remaining life projection with linear and power-law corrosion models
• Processing UT grid CSV data to CTP (Critical Thickness Profile) maps
• Run-repair-replace decision framework

Assessment Levels (API 579-1/ASME FFS-1)

Level	Approach	Input Required
Level 1	Screening — conservative, tabulated equations	Nominal thickness, design pressure, corrosion rate
Level 2	Detailed — refined with actual thickness profiles	UT grid measurements, material properties
Level 3	Advanced — FEA/fracture mechanics	Full material data, specialist analysis

Core Calculations

Remaining Strength Factor (RSF)

from digitalmodel.asset_integrity.rsf_calculations import calculate_rsf, check_ffs_level1

# Level 1 screening — General Metal Loss
result = calculate_rsf(
    t_measured=0.280,    # measured wall thickness (inches)
    t_required=0.150,    # required minimum wall thickness (inches)
    t_nominal=0.375,     # original design wall thickness (inches)
)
print(f"RSF: {result['rsf']:.4f}")        # e.g. 0.7467
print(f"FFS: {result['ffs_acceptable']}")  # True if RSF >= RSF_allowable (0.90)
print(f"MAWP ratio: {result['mawp_ratio']:.4f}")

# Level 1 acceptability check
check = check_ffs_level1(
    t_measured=,
    t_required=,
    t_nominal=,
    design_pressure_psi=,
    smys_psi=,
    outer_diameter_in=,
)
()
()