Non-intrusive Pig Signaller – Hi-T MagAlert: The Hi-T Magalert is a robust non-intrusive magnetic pig signaller used to detect, signal and log the passage of magnetic pigs at critical points along a pipeline. The Hi-T Magalert can be used for both offshore and onshore installations.
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https://www.celerosft.com/en-us/brands/gd-engineering/products/non-intrusive-pig-signaller-devices