How intrusive pig signaller works

Intrusive 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 continuously or intermittently at pre-determined points in the pipeline. Continuous detection is called pig tracking, while intermittent detection is called 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 Signaller


Pig tracking requires an active transmitting source to be attached to the pig, with various technologies being used to provide that source – electromagnetic, acoustic and radioactive. Pig signalling, however, falls into two categories: intrusive and non-intrusive. Non-intrusive signallers are predominantly electromagnetic and, along with pig tracking techniques, are covered more fully elsewhere. Pipeline Engineering has applied its case experience to produce a wide range of intrusive pig signallers.

Intrusive pig signallers are, by definition, static and 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:

  • Mechanical/Visual (a locally flagged indicator)
  • 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.


Intrusive type pig signaller

 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 toward the pig’s travel. The trigger is hinged at two points which converts the angular motion gained from contact with the pig into axial movement 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 the contacts of an externally mounted proximity switch.

Intrusive type pig signaller

When the magnet is withdrawn, the magnetic flux influencing the components diminishes, the flag springs into an upright position, and the proximity switch contact is broken. (A linked controller can detect this). Immediately after the pig has passed, the spring in the cap returns the magnet and the connected 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 to install 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 possibility of pipeline leaks.


non-invasive type of pig signaller


How is the non-invasive type of pig signaller different from the intrusive type in operation?

Pipeline systems use both non-intrusive and intrusive pig signallers to track the passage of pipeline inspection gauges or pigs. Let’s see how these two pigs signallers function:

Pig signaller that doesn’t require any wall modification or penetration: A non-intrusive pig signaller is mounted externally on the pipeline. A sensor that recognizes the magnetic field disruption from a pig’s passage normally makes up this device. This is how it goes:

Magnetic Field Detection: The non-intrusive pig signaller uses a magnetic sensor positioned outside the pipeline, such as a Hall effect sensor or a magnetic switch. The magnetic field around the pipeline is disturbed when a pig travels through it, and the sensor notices this disruption.

The signal produced as an output: When a magnetic field disruption is detected, the sensor has an electrical signal. Usually, this signal appears as a switch closing or a digital pulse.

Signalling Mechanism: A remote monitoring system or control room receives the electrical signal from the sensor. Based on the pipeline operating and monitoring requirements, it can set off alarms or begin other processes to signal the passage of the pig.

Pig signallers not requiring pipeline penetration are typically simpler to install and maintain. They can be used for both new and old pipelines and are less likely to leak or otherwise compromise the integrity of the pipeline.

A mechanical or electronic device must be inserted into the pipeline in order to detect the passage of an intrusive pig signaller, as the name implies. Typically, it entails drilling a hole in the pipeline wall and setting up a device that communicates with the pig.

intrusive pig signaller Here is a description of how it works:

Installation and tapping: To make a small gap in the pipeline wall for an intrusive pig signaller, perform a tapping or hot tapping operation. The pig signaller mechanism is inserted into this aperture.

Pig Interaction: Several approaches to designing the intrusive pig signaller mechanism exist. It might have tangible components that the pig interacts with, such as switches, springs, or flags, which are turned on by the pig’s passage. Alternatively, it might detect the pig using electronic sensors like pressure or proximity sensors.

Output Signal: The intrusive type of pig signaller produces an electrical signal when the pig is detected, much like the non-intrusive type. The signal could be an electrical pulse, a pressure change, or a switch closing.

Similar to the non-intrusive pig signaller, the electrical signal is relayed to a remote monitoring system or control room. It signals the pig passage and sets off the proper reactions or warnings.

To ensure appropriate sealing and the pipeline’s integrity after tapping, intrusive pig signallers must be installed carefully. They could require additional upkeep and present risks from the tapped connection, such as leaking or corrosion.

Overall, elements like pipeline specifications, pig types, maintenance considerations, and operational needs influence the decision between non-invasive and intrusive pig signallers. Both types are used to identify pig passage and are essential to procedures for maintaining pipeline integrity.

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