Leak Detection includes hydrostatic test after pipeline erection and leak detection during service. This article mainly refers to in-service leak detection. Pipeline networks are the most economic and safest mode of transportation for oil, gases and other fluid products. As a means of long-distance transport, pipelines have to fulfill high demands of safety, reliability and efficiency. If properly maintained, pipelines can last indefinitely without leaks. Most significant leaks that do occur are caused by damage from nearby excavation equipment, therefore it is critical to call authorities prior to excavation to assure that there are no buried pipelines in the vicinity. If a pipeline is not properly maintained, it can begin to corrode slowly, particularly at construction joints, low points where moisture collects, or locations with imperfections in the pipe. However, these defects can be identified by inspection tools and corrected before they progress to a leak. Other reasons for leaks include accidents, terrorism, earth movement, or sabotage. The primary purpose of leak detection systems (LDS) is to assist pipeline controllers in detecting and localizing leaks. LDS provide an alarm and display other related data to the pipeline controllers in order to aid in decision-making. Pipeline leak detection systems are also beneficial because they can enhance productivity and system reliability thanks to reduced downtime and reduced inspection time. LDS are therefore an important aspect of pipeline technology. According to the API document “RP 1130”, LDS are divided into internally based LDS and externally based LDS. Internally based systems utilize field instrumentation (for example flow, pressure or fluid temperature sensors) to monitor internal pipeline parameters. Externally based systems also utilize field instrumentation (for example infrared radiometers or thermal cameras, vapor sensors, acoustic microphones or fiber-optic cables) to monitor external pipeline parameters. An OSH glossary used in safety and health at work which is, adopted by ILO {102}. The term definition has been obtained from the secondary source