how to works Intrusive Pig Signaller?

Pig Signaller

Once a pig has been inserted into a pipe system its position cannot be visually confirmed directly. A system is therefore required to indicate a pig’s position, either continuously or intermittently at pre-determined points in the pipeline. Continuous detection is known as ‘pig tracking’ whilst intermittent detection is referred to as pig signalling. Each method involves the use of specialized equipment which, in most instances, must be incorporated into the pig or piping system before the pig is launched.


Pig tracking requires an active transmitting source to be attached to the pig, with various technologies being used to provide that source - electro-magnetic, acoustic and radioactive. Pig signalling, however, falls into two categories: intrusive and nonintrusive. Non-intrusive signallers are predominantly electro-magnetic and, along with pig tracking techniques, are covered more fully elsewhere. 

Intrusive pig signallers are, by definition, static, mechanically actuated and provide a momentary indication of a pig’s presence at a specific point in the pipeline. Because the actuating mechanism is a mechanical trigger that intrudes into the pipeline, a signaller must also incorporate a satisfactory means of retaining the pressure within the pipeline.

Every signaller must incorporate a mechanism that will provide a positive indication that a pig has passed. This is normally done in one of two ways:

  1.   Mechanical/Visual (a local flagged indicator)
  2.   Electrical (magnetically linked proximity switch provides an electrical signal to a controller)

Pig signallers are robust and designed to be installed for long periods. They are particularly suitable for inclusion in a pig trap system at points along the pipeline where the course of the pig must be confirmed (e.g. wyes, diverters, tees) and for providing a warning of approach at receiver and booster stations.


There are two types of Pig Signaller

  •     Intrusive type pig signaller
  •     Non-intrusive type pig signaller 

Intrusive Pig Signaller - Operating Principles

When a pig passes beneath a correctly installed signaller the pig discs push the protruding bi-directional trigger forward in the direction of the pig travel. The trigger is hinged at two points which converts the angular motion gained from contact with the pig into axial motion withdrawing a spring-loaded, permanent magnet holder down through the cap. At rest, the proximity of the magnet at the top of the cap retains the mechanical, spring-loaded flag and/or the contacts of an externally mounted proximity switch.

When the magnet is withdrawn, the magnetic flux influencing the components diminishes, the flag springs into an upright position and/or the proximity switch contact is broken. (This can be detected by a linked controller). Immediately after the pig has passed, the spring in the cap returns the magnet and the linked trigger to their respective resting positions ready to detect the next pig – from whichever direction it arrives. The flag of an MV/MVE must be manually reset. Proximity switches, however, will be reset at the control panel

Non-intrusive type pig signaller

Non-intrusive type pig signaller is quick and Easy for installation on the pipe. There is no hot-tapping required non-intrusive type pig signaller. Non-intrusive type pig signaller can be installed in minutes by any field technician. Non-intrusive means less maintenance and corrosion, and no possibilities of pipeline leaks.

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