The dynamic nature of pipeline integrity and the importance of continual corrosion monitoring for maintaining integrity has been described by Dirk L. van Oostendorp^*. Furthermore, a combination of corrosion assessment techniques (mainly applicable to external corrosion damage) was advocated by this author to maximize "coverage" of corrosion damage and to minimize the disadvantages/limitations of individual techniques (when used in isolation). Assessment techniques based on inferred data were classified as follows:

Category	Examples of Techniques	Increasing detail,  information and confidence in characterizing corrosion damage is obtained by moving down and across this matrix, i.e. by utilizing an increasing number of techniques.
First Pass	Readings at CP test stations
Second Pass	Close Interval Potential Surveys, "Hot spot" surveys
Third Pass	DCVG, Pipeline Current Mapping, C-Scan, Soil Resistivity surveys
Final Pass	Selective excavations, ultrasonic and magnetic flux measurements, microbiological testing

* see reference below

Van Oostendorp made a distinction between the above techniques which are based on inferred data, as opposed to direct inspection (in-line inspection, exploratory digging, bell-hole examinations). All of these techniques/methodologies are important for maintaining pipeline integrity over time.