The literature on pipeline inspections contains a variety of terms to describe changes from the normal condition of a pipe that are found during an inspection. These terms include abnormality, imperfection, anomaly, flaw, and defect. The use of these terms interchangeably makes it difficult to describe a condition in terms of its severity or its impact on the service life of a pipe. A group of terms that provides a clear progression of the extent or severity of unusual pipe conditions would be better understood.

This report uses a consistent set of term to describe conditions that are found during an inspection of a pipeline. The term indication refers to any measured signal above the normal baseline signal recorded by an MFL tool. To determine the cause or source of an indication, additional analysis or interpretation is required.

Classification is the process used to separate the cause of an indication into one of three categories: a non-relevant condition, a pipeline component, or an anomaly. A non-relevant indication is a measured signal from a source outside of the pipe that does not affect the integrity of the pipeline. Examples are foreign objects in the ditch, stray currents, and electrical noise. A pipeline component is a feature, such as a valve or a girth weld, that is a normal part of the pipeline. An anomaly is any kind of imperfection, defect, or critical defect in the pipe wall itself. Note that the terms abnormality and flaw are not used in this report series.

Characterization is the term used to describe the process of assessing the severity of an anomaly from its measured inspection signal or indication. Characterizing is used to classify an anomaly into one of three categories: an imperfection, a defect, or a critical defect.

• The least severe type of anomaly is an imperfection. As used here, an imperfection is an anomaly that may cause failure if the nominal hoop stress in the pipe is at or above the specified minimum yield stress of the pipe material. An imperfection does not usually require repair or removal under existing regulations or industry guidelines, but it may be subject to periodic inspections to assure that it does not grow. Also, measures should be taken to arrest further corrosion.
• A defect is the next more severe type of anomaly. A defect will cause failure of the pipeline at or below the pressure that causes the nominal hoop stress in the pipe to equal the specified minimum yield stress. Defects require repair under existing regulations or industry guidelines, but the repair may or may not be needed immediately.
• A critical defect is the most severe type of anomaly in a pipe. Critical defects are a subset of defects. A critical defect will cause failure at or below the maximum allowable operating pressure of the pipeline. Therefore, immediate action is usually necessary to repair or replace the pipe or to reduce the pressure to a level commensurate with safe operation. As a minimum, an in-line inspection of a pipeline is usually intended to accurately detect and locate all critical defects in the system.