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9 min read•ISO 20669 Non-destructive testing — Pulsed eddy current testing
PEC • Corrosion ScreeningTarget: Corrosion Engineers, API 570 Inspectors, NDT Screening Technicians
Pulsed Eddy Current (PEC) Wall Loss Sizing Guide
ISO 20669 Screening Rules for Insulated Piping & Storage Tanks
Applicable Standards:ISO 20669ASME Sec V Art 21API 570NACE SP0198
Key Technical Takeaways & Execution Rules
- PEC measures average wall thickness over the probe footprint area without removing insulation.
- Footprint size formula: D_f = 2 * (t_pipe + insulation_thickness).
- Signal decay rate (log-log slope d/sqrt(t)) is directly proportional to wall thickness.
- Footprint averaging means isolated pits smaller than the footprint will show a reduced percentage wall loss.
Step-by-Step Field Execution Procedure
1
Insulation & Liftoff Setup
Measure insulation thickness + jacket gap. Input total liftoff parameter into PEC instrument to select correct probe footprint size.
2
Nominal Wall Baseline Calibration
Acquire reference pulse on known uncorroded pipe section of same material grade and nominal thickness.
3
Grid Scan Execution
Perform dynamic grid scan along CUI-susceptible locations (support shoes, elbows, low points). Record wall thickness percentage (% nominal).
Probe & Wedge Selection Specs
Code Acceptance Criteria
ISO 20669 / API 570: Locations exhibiting >25% wall loss flag mandatory follow-up UT or tangential radiography inspection.
Apply This Technique in the Field