Leak detection (and localization) systems (LDS), especially due to legal regulations like
• the “Code for Federal Regulations (CFR) Title 49 Part 195” , API 1130 2nd Ed. , both for the USA, or
• the “Technische Regeln für Fernleitungen” (TRFL) (Technical Rules for Pipelines) in Germany .
This paper gives an overview of methodologies, methods and techniques for leak detection and localization;  and  are two other interesting sources giving an overview.
Some remarks concerning (legal) regulations both for the USA and for Germany will be shown in chapter 1. Chapter 2 summarizes the requirement to LDS considering reliability, sensitivity, accuracy, and robustness.
These terms had been defined with respect to LDS within API 1155 , and will be explained in some detail within this chapter 2.
External systems. External based LDS (due to API 1130 2nd Ed.) use local leak sensors to generate a leak alarm. Acoustic emission detectors, fiber optical sensing cable, vapor sensing cable and liquid sensing cable based systems are shortly presented in chapter 3.
Internal systems. Internal based LDS (also due to API 1130 2nd Ed.) use normal field sensors (e.g. flowmeters) for leak detection and sometimes leak localization. A significant part of the paper (chapter 4) deals with these internally based systems like
• balancing systems (line balance, volume balance, compensated mass balance etc.),
• Real Time Transient Model LDS (RTTM-LDS),
• pressure/flow monitoring, and
• statistical analysis LDS.
Different methods for leak localization (gradient intersection method, wave propagation analysis etc.) will be shown in chapter 5.
Extended RTTM. The presentation of an Extended RTTM approach (E-RTTM) combining advantages of conventional RTTM LDS and statistical systems follows in chapter 6, together with the demonstration of applicability by means of two examples,
• a liquid multi-batch pipeline, and
• a gas pipeline.
PipePatrol. The University of Applied Sciences in Gelsenkirchen and KROHNE Oil & Gas B.V. from Netherlands (KOG) closely work together on the field of leak detection. The outstanding properties of the E-RTTM technology therefore motivates KOG to choose E-RTTM for PipePatrol, the KOG leak detection and localization system.