High and medium pressure pipelines passing under main roads, rivers or centres of population may require additional protection against corrosion. One of the methods used is to encapsulate the pipeline with a metal “sleeve” filled with Nitrogen, an inert gas that prevents the external pipe wall surface from corroding. The nitrogen gas is typically pressurised to 1 bar (100kPa).
For this method to be effective, the pressure of the nitrogen in the sleeve has to be maintained. This means operators must check the pressure in the sleeve periodically to make sure that it is not leaking.
If the pressure has dropped to an unacceptable level, the sleeve must be refilled with nitrogen, which can be a very labour-intensive activity since the gas containers are heavy and bulky to carry and the fill points are often difficult to access.
With many older pipelines encapsulated by sleeves, it is important that the nitrogen does not leak out and so the sleeves must be regularly checked to ensure that they are maintaining the correct pressure. Refilling sleeves is highly labour-intensive so, if the gas is leaking, the operator can monitor the pressure drop and schedule maintenance accordingly.
Two types of sleeve monitor are available; the MERLIN Nitrogen Sleeve Monitor which fits inside an plastic post or kiosk and the MERLIN Communications Module with Nitrogen Sleeve Adaptor which fits inside a M28 or alternative sleeve fill point.