On oil pipelines, isolating block valves fitted with automatic line-break-operators are typically installed on either side of river crossings.

Low pressure shutoff only works when there is major rupture of the oil or gas pipeline - it doesnt detect low pressure when there are small to medium sized ruptures. Small ruptures are far more common and these usually can be traced back to internal and/or external corrosion. Too bad, many cross country pipelines are built with cheap carbon steel even when traversing environmentally sensitive / water catchments / agricutural land / high population areas.

An oil pipeline only needs to lose the pump capacity per second plus the tiny mass required to raise the pressure to operating pressure, a few hundred barrel leak will depressurize the line. Rapid pressure-drop sensors work fine.

In a gas line you also have to remove the mass that was added to raise the pressure to operating pressure. That is a staggeringly large volume, whose rate of flow is limited by sonic velocity. A long pipeline might take several minutes for a major leak to even cause a noticeable change in pressure. Rapid pressure-drop sensors don't work very well. Typically remote isolation valves trip on a minimum static pressure without looking at the rate of change.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

Carlos,
The response from David is for the case when there is no flow through the leaking pipeline (pipeline is shut in under pressure), while my response is for the case when there is flow through the leaking pipeline.

This is getting into the realms of leak detection and how to control any leak.

Most liquid pipelines respond well to many different forms of leak detection and all respond well to large / medium leaks.

Remote controlled actuated block valves are the normal operation now, but not many are fitted with any type of automatic system, mainly due to the potential for false operation or having to set the parameters so high that they are ineffective in operation. Most pipeline operators distrust any automatic shutdown system based on even the most sophisticated leak detection systems and at best have a certain window ( 45 to 60 seconds) built in to allow the operator to override a shutdown.

On liquid lines you can get normal operational and transient activities which can result in pressure falling quite rapidly, e.g. pump start / stop, start up of the line, change of routing and flow to different places. To prevent inadvertent closure you therefore need to set the rate of fall really quite high and hence they may only work in extreme full bore rupture scenarios which are relatively easy to see on a control screen.

So bottom line, no I don't think they are effective but they do seem to give non technical people / Environmental consultants some comfort that there is a system there which acts "automatically" so sometimes they get fitted for that reason alone.

George - I didn't get the thinking behind the "cheap carbon steel" bit. I would hazard a guess that 99% of high pressure cross country pipelines are built from carbon steel. If they are suitably designed, constructed, tested, operated, inspected and maintained in the correct manner then their chance of leakage is very small. The risk from third parties remains the single biggest cause of pipeline leaks which could happen if the pipeline was built of Duplex, but then the cost would be horrendous.

I assume you mean small pin hole leaks, not ruptures. There's no such thing as a small rupture....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Thanks everyone for you response.
zdas04, I understand. For this motive gas pipeline has line break and low pressure shut off system and oil pipeline has line break system.
LittleInch your how know and expertise about which is used now help me very much. Thanks!