Comparative Reference Card · Rev. 2 · DELTA TEST ME LLC
ECT
Conventional Eddy Current
Applicable for: All non-magnetic materials (SS, Cu-Ni, Ti, Inconel, brass)
Advantages
- +Suitable for all paramagnetic / non-magnetic metals
- +Very good defect depth & size estimation (phase)
- +Internal + external defects (ID/OD)
- +Suitable for WT up to ~5 mm
- +High speed — up to 100 tubes / h
- +Tube-sheet area with rotating probes
- +Defects under baffle plates detectable
- +Cracks (circumferential + longitudinal)
- +No coupling medium (water) needed
- +Cleaning less stringent than IRIS
- +Defect type need not be known in advance
Disadvantages / Limitations
- −Not applicable for ferromagnetic tubes (CS, LAS)
- −Magnetic deposits → false signals
- −No absolute wall thickness
- −Skilled personnel required (calibration)
- −Reference standard must match production tube
PSEC
Partial Saturation EC
Applicable for: Slightly / partially magnetic (Duplex, super-duplex, CW SS, thin CS)
Advantages
- +Bridges the µr gap between ECT and FSEC
- +Internal + external corrosion
- +Cracks (circ. + long.) — phase preserved
- +ID/OD discrimination via phase
- +Defects under baffle plates
- +High speed — up to 70 tubes / h
- +U-bend capable (compact magnet)
- +Tube-sheet area with rotating probes
- +No coupling medium needed
- +Same instrument as ECT and FSEC
- +Covered by ASTM E2884
Disadvantages / Limitations
- −Mixed defect types hard to interpret
- −Depth via amplitude in saturated zones
- −No absolute WT measurement
- −Highly skilled personnel required
- −Accuracy ± 10 % to ± 20 %
- −Sensitive to material variations
FSEC
Full Saturation EC
Applicable for: Strongly ferromagnetic (CS, LAS, T11, T22, P91, ferritic SS)
Advantages
- +DC bias → permeability noise eliminated
- +Internal + external corrosion
- +Stable, predictable skin depth
- +ID/OD discrimination via phase
- +Defects under baffle plates
- +General wall loss reliably detected
- +High speed — up to 70 tubes / h
- +Tube-sheet area with rotating probes
- +No coupling medium needed
- +Same instrument as ECT and PSEC
- +Covered by ASTM E2884
Disadvantages / Limitations
- −Heavy magnet → straight sections only
- −Crack signature flattened by saturation
- −Mixed defect types hard to interpret
- −No absolute WT measurement
- −Highly skilled personnel required
- −Accuracy ± 10 % to ± 20 %
- −Larger probe diameter than ECT/PSEC
RFT
Remote Field Testing
Applicable for: Ferromagnetic CS / LAS (heavy wall > 4 mm)
Advantages
- +Effective for heavy-wall ferromagnetic tubes
- +Inspection speed considerably > IRIS
- +No coupling medium needed
- +Tolerant to scaling / less cleaning effort
- +Cracks (circumferential) detectable
- +Equal ID/OD wall-loss sensitivity
Disadvantages / Limitations
- −Not applicable for finned ACHE tubes
- −Not sensitive to small local defects
- −No reliable ID/OD discrimination
- −Cannot detect defects under baffle plates
- −Mainly limited to general wall loss
- −10 – 20× slower than EC family
- −Compressed phase-vs-amplitude dynamic range
- −Highly skilled personnel required
NFT
Near Field Testing
Applicable for: Ferromagnetic finned ACHE tubes (OD wall loss + fin-root corrosion)
Advantages
- +Optimized for ACHE finned tubes
- +Detects fin-root corrosion (bobbin EC may miss)
- +Internal probe — no external access required
- +Faster than RFT (~ 0.3 – 0.6 m/s)
- +No coupling medium needed
- +Tolerant to fin geometry
Disadvantages / Limitations
- −Niche method — finned ACHE tubes only
- −Qualitative output (amplitude-based)
- −Limited crack sensitivity
- −WT range limited to 1 – 3 mm
- −Manufacturer-specific calibration
- −Cannot replace bobbin EC for ID-side defects
MFT
Magnetic Flux Leakage
Applicable for: Ferromagnetic CS only (requires external magnet contact)
Advantages
- +General + localized corrosion in CS tubes
- +Cracks (circumferential) detectable
- +Fin-fan tubes with external geometry access
- +No coupling medium needed
- +Tolerant to internal scale / deposits
Disadvantages / Limitations
- −Not for general gradual erosion
- −Sizing of pits / defects not reliable
- −Defects under baffle plates difficult
- −Irregular pulling speed → misinterpretation
- −Bad data on rough surfaces / scaling
- −High set-up effort, error-prone
- −Highly skilled personnel required
- −No near-/far-surface discrimination
- −Longitudinal cracks not detected
- −Slower than FSEC
- −Excluded from ACHE, U-bends, insulated tubes
IRIS
Internal Rotary Inspection System
Applicable for: All materials (incl. non-metals) — verification tool, not for screening
Advantages
- +Absolute wall thickness in mm (high accuracy)
- +Excellent defect geometry quantification
- +Excellent defect size quantification
- +Internal + external defects equally well
- +Defects under baffle plates
- +Suitable for general wall loss
- +All material types (material-independent TOF)
- +Provides datum for API 579 FFS
Disadvantages / Limitations
- −Misses small pin holes (e.g. 1 mm dia. in SS)
- −Very low speed (max. 6 – 12 tubes / h)
- −High cost per tube due to low throughput
- −Bare-metal cleaning essential
- −Water coupling mandatory
- −"Dirt reflection" causes false signals
- −Pulling speed critical for 100 % coverage
- −Pulling speed normally not closed-loop
- −Water turbidity < 5 NTU required
- −Skilled personnel for false-signal rejection
- −Hard to apply in confined-space entry
- −Tube must be filled with water
- −U-bends cannot be inspected
- −Sensor centring critical
Author: Stefan Köllner, DELTA TEST ME LLC · Comparative Reference Card, Rev. 2