MFL vs eddy current testing

Two electromagnetic methods, two different networks. MFL quantifies wall loss on larger lines; eddy current reaches small-bore pipe. This comparison maps each to its defects.

Factor	Magnetic flux leakage (MFL)	Eddy current
Principle	Magnetise the wall; sensors read flux leaking at metal loss	Induced currents in the wall; sensors read flow disturbance at defects
Diameter range (this line)	159–1,422 mm across 20+ tool specifications	Down to DN65
Best at	Volumetric metal loss: corrosion, mechanical damage, through-wall quantification	Holes and large-area corrosion (>15%); small-bore gathering and city-gas lines
Recorded threshold	Features located to +/-0.1 m of girth weld, +/-5 degrees circumferential	10 mm x 10 mm x 15% or deeper internal defects
Known blind spots	Field-parallel cracks, pinholes, circumferential-weld anomalies are harder	Depth sizing on thick wall is limited vs MFL; screening role on large lines
Run envelope (this line)	0–10 MPa, -10–80 C, 60+ h runs, 1.5D bends	0–10 MPa, -10–80 C, 50+ h runs, 1.5D bends

How to decide

Ask two questions. What diameters? Below 159 mm, MFL in this line does not go — the eddy current machine owns DN65 and up. What decision follows the data? If you must size wall loss to schedule repairs on a trunk line, MFL's quantification is the tool — start with the MFL fleet. If you must screen many small lines for through-holes and heavy corrosion, eddy current's reach wins.

Why programmes run both

Real networks contain both problems. The standard architecture in this line: MFL for trunk and transmission lines, eddy current for gathering and distribution, and a shared reporting discipline so both feed one integrity register — structured in the pipeline inspection guide. The methods are complements wearing similar enclosures, not rivals.

None

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