Pipeline Anomaly Categorization According to POF

Anomaly categorization is essential for interpreting ILI results and selecting the correct integrity-assessment method. Under POF 100, anomalies should be described by their surface location, anomaly type, and dimensions.

1. Surface Location

• Internal: Located on the pipe’s inside surface and commonly associated with the transported product, water accumulation, solids, or internal operating conditions.
• External: Located on the outside surface and commonly associated with coating failure, inadequate cathodic protection, soil conditions, or external interference.
• Mid-wall: Located within the pipe wall, such as laminations or inclusions.
• Combined: Features occurring at the same location but on both the internal and external surfaces.
• Not identified: Used when the inspection technology cannot confidently distinguish the surface location.

2. Anomaly Type

POF defines metal loss as a volumetric anomaly in which pipe material has been removed. It should be further identified according to its likely origin:

• Corrosion: Metal removal caused by an electrochemical reaction. It may be internal or external.
• Gouging: Elongated grooves or cavities caused by mechanical contact with a foreign object.
• Grinding: Intentional wall-thickness reduction caused by hand filing or power-disc grinding.
• Mill anomaly: An anomaly introduced during the manufacture of the pipe or component.
• Mechanical damage: A broader category that may include dents, gouges, spalling, or combinations of deformation and metal loss.

The cause and the geometry should not be confused. For example, external corrosion describes the location and origin, while axial grooving describes the geometry.

3. Metal-Loss Dimensional Classification

POF classifies metal-loss anomalies using:

• ll: Axial length
• ww: Circumferential width
• tt: Pipe-wall thickness
• AA: Geometrical reference parameter

Where:

• If t<10t < 10 mm, then A=10A = 10 mm.
• If t≥10t \geq 10 mm, then A=tA = t.

Pinhole

Pitting

Axial grooving

Circumferential grooving

Axial slotting

Circumferential slotting

General metal loss

Conclusion

A complete anomaly description should answer three questions:

1. Where is it? Internal, external, mid-wall, or combined.
2. What caused or created it? Corrosion, gouging, grinding, manufacturing, or another mechanism.
3. What is its geometry? Pinhole, pitting, grooving, slotting, or general metal loss.

Keeping these categories separate produces clearer ILI reports, supports correct tool-performance evaluation, and helps engineers select the appropriate assessment method.

Reference: POF 100 – Specifications and Requirements for In-Line Inspection of Pipelines, November 2021.