Many tanks in a tank farm are kept under a slight blanket of nitrogen to keep air and moisture out of the vapor space above the product. But holding that blanket is not a set-and-forget thing, because the vapor space keeps changing: pump product out and the space grows, cool the tank at night and the vapor contracts, and either way the pad pressure wants to fall. The nitrogen blanketing supply is the makeup side of the system, the part that adds nitrogen to keep the pad pressure up when it would otherwise drop. This page explains the demand regulator or control valve that supplies that makeup, how it coordinates with the relief side, how the nitrogen header serves many tanks, and how consumption and pad pressure show up in SCADA.
Nitrogen Blanketing Supply in one line: A nitrogen blanketing supply is the makeup side of tank blanketing that adds nitrogen to a tank's vapor space to hold its pad pressure as the level drops or the temperature falls. It uses a demand regulator or a control valve that opens to admit nitrogen when pad pressure falls toward its low setpoint and closes once pressure recovers. This makeup control is coordinated in split range with the relief side, so nitrogen is added at low pressure and vapor is vented at high pressure, and the nitrogen is drawn from a header that serves many tanks across the farm.
The core of the blanketing supply is a device that admits nitrogen into the tank's vapor space whenever the pad pressure falls below a setpoint. In its simplest form this is a demand or makeup regulator, a self-contained valve that senses the tank pressure and opens to let nitrogen in as the pressure drops, then closes again as pressure is restored, all mechanically without needing a controller. In more instrumented installations it is a control valve driven by a pressure controller that reads the pad pressure and modulates the valve to hold a setpoint. Either way, the job is the same: keep the vapor space at a small positive pressure by adding nitrogen on demand.
The demand for makeup comes from two directions. The first is level: as product is pumped out of the tank, the liquid surface drops and the vapor space above it grows, so the same amount of gas now occupies more volume and the pressure falls, calling for makeup nitrogen to fill the extra space. The second is temperature: as the tank and its vapor cool, for instance overnight or when cold product is received, the vapor contracts, again lowering the pressure. Both effects pull the pad pressure down, and the supply valve responds by admitting nitrogen to hold the pressure where it belongs.
Holding a small positive pad pressure is the whole point, because it is what keeps the tank inerted. If the pressure were allowed to fall to atmospheric or below, air could be drawn in through vents or leaks, bringing oxygen and moisture into the vapor space, which for many products is exactly what the blanket exists to prevent. By supplying nitrogen the moment the pressure sags, the makeup side ensures the vapor space stays nitrogen-rich and slightly pressurized, so ingress of air is prevented rather than merely diluted after the fact.
The supply side does not work alone; it is one half of a pressure control that also has a relief side, and the two are coordinated in split range so they never fight each other. The pad pressure is meant to sit in a band between a low setpoint and a high setpoint. When pressure falls to the low setpoint, the nitrogen supply opens to add gas; when pressure rises to the high setpoint, for instance when the tank is being filled and the vapor space is shrinking, the relief side opens to vent excess vapor. Between the two setpoints, in the normal band, both are closed and nothing happens. This split-range arrangement means nitrogen is only added when genuinely needed and vapor is only vented when pressure is genuinely high, so nitrogen is not wasted by supplying and venting at the same time.
The gap between the makeup setpoint and the relief setpoint matters. If the two setpoints are too close, the tank can end up supplying nitrogen and then venting it moments later as normal breathing swings the pressure across both points, wasting gas. A properly spread band lets the pad pressure drift within the normal range without triggering either device, so nitrogen is consumed only for real demand from level and temperature changes, not for ordinary noise in the pressure. Tuning that band is part of making a blanketing system economical as well as safe.
Because a tank farm has many tanks, the nitrogen is usually distributed through a header, a supply line running across the farm that feeds each tank's makeup valve. That header has to be sized so it can meet the combined demand of the tanks it serves, including the worst realistic case where several tanks call for makeup at once, such as during simultaneous pump-out or a cold night across the whole farm. If the header cannot deliver enough nitrogen at adequate pressure, tanks that are drawing hard will not hold their pad pressure, so the header sizing is not just a supply detail but a factor in whether the blanket holds under peak demand.
Bringing pad pressure and nitrogen use into SCADA turns blanketing from a set of local mechanical regulators into something the terminal can actually watch. The pad pressure of each tank is the primary indication, because that is what the whole system exists to hold, and seeing it live tells operators whether every tank is sitting comfortably in its band or whether one is riding low and struggling to hold the blanket. Alarms on pad pressure catch a tank whose supply cannot keep up or whose relief is venting too readily, before the blanket is lost.
Nitrogen consumption is the other signal worth trending, because it is both a cost and a diagnostic. A tank or a farm that suddenly starts consuming far more nitrogen than usual is telling you something: perhaps a valve stuck open, a leak in the vapor space, a relief device passing, or simply heavy pump-out. Trending consumption over time lets the terminal separate normal demand, which tracks how much product is being moved and how the temperature swings, from abnormal demand that points at a fault. Without the trend, a leaking tank quietly burns through nitrogen and no one notices until the bill or the supply runs short.
For a terminal using cloud monitoring, having pad pressures and nitrogen consumption historized across the whole farm is what makes the blanketing system manageable at a distance. A platform such as Merobix can trend each tank's pad pressure and the overall nitrogen draw so operators see both the immediate state and the longer pattern, catching a tank that is slowly losing its ability to hold pressure or a header that is straining under combined demand. That visibility turns nitrogen blanketing from a system you only think about when it fails into one you can supervise proactively, which matters because the failure mode, air getting into an inerted tank, is exactly the outcome the blanket exists to prevent.
Because the vapor space keeps losing pressure and the blanket has to be topped up. As product is pumped out the vapor space grows, and as the tank cools the vapor contracts, both of which lower the pad pressure. The makeup supply admits nitrogen whenever the pressure falls toward its setpoint, keeping a small positive pressure so air and moisture cannot be drawn into the inerted vapor space.
The two are coordinated in split range with separate setpoints and a normal band between them. The supply opens only when pressure falls to the low setpoint, and the relief vents only when pressure rises to the high setpoint, so in the normal band both stay closed. Spreading the setpoints far enough apart keeps ordinary pressure swings from triggering both, so the tank does not add nitrogen and then vent it moments later.
It is both a cost and a diagnostic. A tank or farm that suddenly consumes far more nitrogen than usual may have a stuck-open supply valve, a leak in the vapor space, a relief device passing, or simply heavy pump-out. Trending consumption over time separates normal demand, which tracks product movement and temperature swings, from abnormal demand that points at a fault, so a leaking tank is caught before it quietly drains the supply.
Merobix reads your field devices into a cloud SCADA - the real thing behind these terms, live in days from any browser.