Non-intrusive leading the way

Pigging plays a key role in the pre-commissioning, inspection and maintenance of pipelines and pig signallers are crucial to confirming the successful launch of pigs, ensuring they navigate critical or challenging sections of the pipeline and ultimately verifying they have been received. In recent years, the industry has been shifting towards the adoption of non-intrusive pig signallers over intrusive models but despite the obvious benefits of non-intrusive, intrusive signallers are still widely used. This article will explore these benefits and the different technologies on the market and how they operate as well as providing recommendations on selecting the correct technology for the application at hand.

Understanding pig signallers

Pig signallers, sometimes known as pig detectors, are devices designed to identify and signal the passage of pigs. Their primary purpose is to alert the operator when the pig has been launched and received and when it passes specific locations or conversely, a lack of signal can indicate that a pig has stalled in the pipeline. If this happens, pig signallers can be used to narrow down the search area before employing the use of a pig locating system. For example, if a signaller does not trigger but the previous one does, the operator can conclude that the pig is located between these two signallers.

There are two types of pig signallers; Intrusive signallers are mechanical devices that indicate the passage of a pig when it pushes against the trigger inside the pipeline as it moves through. In contrast, non-intrusive devices detect pigs without penetrating the pipeline. They utilise technologies, such as acoustic and magnetic, to identify the pig as it passes. Non-intrusive signallers can be easily strapped to the pipeline using ratchet straps or stainless-steel banding.

Technology overview

Before diving further into the many smart features and advantages of non-intrusive signallers, an overview of the technologies and their principle of detection will be presented. While each technology has a unique detection method, there are some common features. Upon pig detection, the signallers activate an alert, utilising visual signals like flashing LEDs or remote notification to a control room or handheld device. The passage data, including date and time is logged for future reference with up to 100 events being stored. After alerting the detection locally or remotely, the signallers reset after a predetermined time, ensuring readiness for the next pig. Manual reset options via a push button or control room are also available.

Magnetic

Magnetic pig signallers, while not a novel technology, have undergone a significant evolution, becoming more reliable, customisable and intelligent over the years. These signallers operate with any pipeline medium – the only requirement is that the pig is carrying magnets.

A magnetic sensor is integrated within the unit housing or provided on a cable for buried or restricted access pipelines. As the pig approaches, the sensor detects the rising magnetic field and if it reaches the set threshold, an ‘Approach’ is registered on the signaller. As the pig moves past the signaller along the pipeline, the magnetic signal decreases, triggering the pig passage.

The sensitivity to magnetic changes ensures precise and timely detection, making magnetic signallers a preferred choice for many pipeline operators.

Ultrasonic

Ultrasonic pig signallers provide a sophisticated approach to pig detection in liquid lines, distinguishing themselves from other models by detecting both the passage of a moving pig and the position of a stationary one, without the need for magnets or transmitters.

Equipped with an ultrasonic transducer on a cable, the signaller uses the pulse-echo method to detect the time of flight of ultrasonic pulses through the pipe. A pulse is sent through the pipe wall and if the line is filled with liquid the unit can detect a reflection from the other side. When a pig passes, disturbing the fluid path, the interruption of the reflection is identified, and pig passage detected. Calibration of the detection algorithm allows the signaller to identify and ignore smaller objects, further enhancing the accuracy. An ultrasonic pig signaller is unique in its ability to precisely locate a stationary pig by moving the ultrasonic sensor along the pipeline and measuring the reflection. This prevents delays in establishing position especially after the mainline tee but before the pig receiver isolation valve where the pig can lose momentum and stall.

Acoustic

Acoustic pig signallers, operating on sound detection, offer versatility in any pipeline medium without requiring magnets or transmitters. They monitor the acoustic emissions from the vibrational and acoustic noise produced by a moving pig in the pipeline and advanced detection algorithms filter out irrelevant noise. To avoid false positives, it is preferable not to install these units near pipeline features that could potentially have a noise profile similar to that of a pig such as a valve, however all valve line up activities should be completed before the pig is launched. Upon identifying the sound of a pig approaching, the unit signals ‘Pig Approach’ and as the sound level decreases it signals ‘Pig Passage’.

The application at hand

Meaningful understanding of the application and types of pigs the operator will use and why should be considered. On paper, acoustic signallers appear to be the obvious choice due to their versatility in any medium and with any pig. This may be true when considering a pipeline away from background noise but…

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