General corrosion

Corrosion with dimensions of length and width extending to three times the wall thickness or greater.

Spiral corrosion

Corrosion occurring in a spiral orientation around the pipe, usually due to tenting of tape coatings at the spiral weld, or water ingress under the spiral wrap of a tape coating.

NAEC

Narrow axial external corrosion along the seam weld due to tenting of tape coatings at the weld bead.

Grind marks

Grinding out of minor surface defects, usually during the pipe manufacturing process.

Girth weld corrosion

Corrosion at or adjacent to the girth weld bead, often due to problems with the field coating over the girth weld.

Girth weld lack of penetration

Inadequate energy input at the girth weld, resulting in an incomplete weld.

General wall thinning

Can be due to slab corrosion or erosion effects.

Gouging

Mechanically induced damage that causes localized reduction in wall thickness. The remaining metal in a gouged area is often work-hardened, which can change its magnetic properties. A gouged area may include shallow cracks that further reduce the pressure-carrying capability of the pipe.

Erosion wall thinning

Gradual thinning of the pipewall, for example due to impact of sand particles in the pipeline product.

Cavitation

Erosion of the pipe caused by cavitation in the liquid product due to pressure drops, for example downstream of girth weld beads. This can lead to fingers of corrosion that eventually join to form 'plateau corrosion' over large areas.

Pitting

This type of corrosion affects only a small area on the pipeline surface. Local concentrated-cell corrosion on the internal or external surfaces of the pipe results from a voltage difference caused by variations in oxygen concentration inside and outside the pit. The oxygen-starved pit acts as the anode and the pipe surface acts as the cathode. The term "pitting" is applied when the maximum surface dimension is no greater than three times the wall thickness.

Channelling corrosion

Long axial corrosion, usually at the 6 o'clock position in a pipe, caused by water lying at the bottom of the pipe.

Seam weld corrosion

Preferential corrosion at the seam weld, for example in ERW welds due to material properties of the steel in the heat affected zone.

Bacteria corrosion

Corrosion often caused by sulfur reducing bacteria in the pipeline product.

Laminations

Although they are not technically metal loss, laminations are manufacturing defects caused by inconsistencies in the material used to manufacture the pipe. They may break the surface or be buried within the pipewall. Laminations may be located using ultrasound NDT techniques.