NACE Standard Report (3T199) "Techniques for Monitoring Corrosion and Related Parameters in Field Applications" describes several techniques to monitor corrosion and classifies them into intrusive non-intrusive online and offline techniques. Some of these techniques are used during the detailed examination step of the Internal Corrosion Direct Assessment (ICDA) process Nonintrusive measurement techniques avoid any risks associated with insertion inside the pipeline and retrieval operations of intrusive techniques. These techniques have the advantage of monitoring the actual pipe rather than monitoring test specimens as required by intrusive monitoring probes. The non-intrusive techniques can be attached at critical locations such as welds pipe bends tees drips and similar non-uniform locations where intrusive direct techniques such as inline inspection cannot be used without extensive system modification. A wide range of non-intrusive measurement techniques is available but each technique has its strengths and weaknesses. In this paper results from a 10-year experiment carried out to evaluate the merits and demerits of five non-intrusive techniques (handheld ultrasonic fixed ultrasonic electrical probe hydrogen permeation and fiber optic) will be presented.