DVGW Research Confirms: CMI Detects Pipeline Corrosion Where Conventional Methods Fail
DVGW Publishes NEMEK Final Report — A Milestone for Pipeline Corrosion Assessment
The DVGW has published the final report of the research project NEMEK (G 202329) — "Neue Methodik zur externen Korrosionsbewertung an kathodisch geschützten Rohrleitungen" (New Methodology for External Corrosion Assessment on Cathodically Protected Pipelines). Conducted with six major European gas transmission operators — GASCADE Gastransport GmbH, ONTRAS Gastransport GmbH, Open Grid Europe GmbH, Westnetz GmbH, Swissgas AG, and Thyssengas GmbH — this independent research validates Current Magnetometry Inspection (CMI) as the first above-ground survey method capable of determining the corrosion state at individual coating defects.
The Problem: Conventional Methods Detect Coating Defects — But Not Corrosion
Standard above-ground survey methods such as DCVG (Direct Current Voltage Gradient), CIPS (Close Interval Potential Survey), and Intensive Measurement (IM) have been industry practice for decades. They reliably identify coating defects — but they share a fundamental limitation: they cannot determine whether active corrosion is occurring at a detected defect, or whether the steel is protected by a passive calcareous film.
The NEMEK report quantifies the consequence: Intensive Measurement (IM) produces a false negative rate of 68.4 % for E_IR-free assessment, and CIPS achieves only 64.9 % true positive rate. In practice, this means that up to 95 % of excavations triggered by conventional methods are operationally unnecessary — causing significant cost and disruption without improving pipeline safety.
NEMEK Results: CMI Achieves 99.96 % Reliability Across 6,672 Defects
The NEMEK project evaluated CMI across real operating pipelines of six gas transmission operators. The core metric — protective layer formation (Deckschichtbildung) at coating defects — was assessed using CMI's patented frequency-dependent spread resistance analysis. The results:
- 6,672 coating defects detected and classified across all project pipelines
- Active corrosion confirmed at excavation in only 3 cases — a method reliability of 99.96 %
- CMI E_IR-free determination: 90.9 % true positive rate (vs. 31.6 % for IM, vs. 64.9 % for CIPS)
- CMI E_IR-free false negative rate: 4.5 % (vs. 68.4 % for IM)
- Protective layer formation assessable for 100 % of detected defects — IM achieved only 79 %
These findings confirm that CMI is the only above-ground method that combines coating defect detection with reliable corrosion state classification in a single inspection run.
How CMI Classifies Corrosion State at Each Defect
Where conventional methods stop at detecting a coating holiday, CMI determines the electrochemical condition of the steel beneath. By applying a multi-frequency AC current (2 Hz – 2 kHz) and analysing the frequency-dependent spread resistance and phase angle at each defect, CMI distinguishes between:
- Passivated defects: A protective calcareous layer has formed — the spread resistance increases with decreasing frequency, indicating a capacitive barrier. The corrosion cell is electrically blocked. These defects require monitoring only.
- Active corrosion: No protective layer — the spread resistance remains constant across frequencies, indicating ohmic current flow through bare steel in direct soil contact. Excavation and repair are required.
Crucially, CMI does not disrupt cathodic protection during measurement — unlike DCVG, which requires potential swings of up to 25 V that shift the pipeline's E_on in the cathodic direction, increasing the risk of AC corrosion and coating disbondment.
What NEMEK Means for Pipeline Operators
The NEMEK final report provides independent, peer-reviewed evidence that CMI fundamentally changes the economics and reliability of external corrosion direct assessment (ECDA). For pipeline operators, this means:
- Fewer unnecessary excavations: By distinguishing active corrosion from passivated defects, CMI eliminates the vast majority of excavations that conventional methods trigger without justification
- Reliable E_IR-free assessment: CMI achieves 90.9 % true positive rate for E_IR-free — enabling accurate verification of cathodic protection effectiveness per ISO 15589-1
- Complete defect assessment: Every detected coating defect receives a corrosion state classification — no gaps, no unassessable defects
- No disruption to cathodic protection: Inspections run without shutdowns, without shifting E_on, and without operational impact
Access the NEMEK Report
The NEMEK final report (DVGW research project G 202329) is available through the DVGW. To discuss how CMI-based inspection can improve your pipeline integrity programme, contact our team.