Base on the actual experience of online maintenance and statistics data of related organizations, the authors elaborated the essentiality and significance regarding the online testing for the emergency shutdown valve of Safety Instrumented System, and emphatically recommended the three means of Partial Travel Testing, including their advantages, disadvantages, and application examples, etc.

A comparison is made of advantages and defects among protective measures,including adopting advanced imported regulator,installing fast isolating valve in front of regulator,using two-circuit regulator plus fast isolating valve,installing excessive underpressure automatic isolating valve in front of domestic gas meter etc.