A moisture analyzer measures how much water vapor is in a natural gas stream, the number that tells an operator whether the gas has been dried enough to enter a pipeline. Water in gas causes hydrates, corrosion, and freeze-ups, so pipelines set a firm moisture limit and every facility has to prove it meets that spec. This guide explains what the analyzer measures, the common measurement technologies, and how the reading is used to verify dehydration.
Moisture Analyzer in one line: A moisture analyzer is an online instrument that continuously measures the water-vapor content of natural gas, usually reported as pounds of water per million standard cubic feet (lb/MMscf) or as a water dew point. It verifies that dehydration equipment is drying the gas to within the pipeline's moisture specification, using technologies such as tunable diode laser absorption, chilled-mirror dew point, or a moisture-sensitive element.
Wet natural gas has to be dried before it goes into a sales pipeline, and the moisture analyzer is the instrument that confirms the job is done. Water content in gas is expressed two ways that describe the same thing. One is a concentration, pounds of water per million standard cubic feet, lb/MMscf, which states how much water the gas carries. The other is the water dew point, the temperature at which that water would start to condense out at the operating pressure; a lower dew point means drier gas. Pipelines typically specify a maximum water content or a maximum dew point that incoming gas must meet.
Several measurement technologies are in use. A tunable diode laser absorption spectroscopy (TDLAS) analyzer shines a precise laser wavelength through the gas and measures how much light the water vapor absorbs, giving a fast, non-contact reading that does not touch the sample and resists contamination. A chilled-mirror instrument cools a small mirror until dew forms and detects that first condensation optically, reading the dew point directly as a fundamental measurement. Older and simpler designs use a moisture-sensitive element, such as a metal-oxide or capacitance sensor whose electrical property changes with absorbed water.
Whatever the sensing principle, the analyzer works on a conditioned sample: gas is taken off the line, its pressure and temperature are managed, and any liquids or contaminants are removed so the instrument sees clean vapor. Sample handling is a big part of a reliable moisture measurement, because a poorly designed sample line can add or lose water and give a misleading result no matter how good the analyzer is.
The reason to install a moisture analyzer is to prove and protect gas quality. Upstream of it sits the dehydration equipment, most often a glycol dehydration unit or a solid-desiccant bed, whose job is to strip water out of the gas. The analyzer is the check on that equipment: if the dehydration is working, the outlet gas reads below the moisture limit, and if the reading climbs, something in the drying process is failing, well before the gas reaches a custody point where it could be rejected or cause a problem.
This distinguishes the analyzer from the dehydration process itself. A glycol dehydration unit is the equipment that removes the water, and dew-point control describes the broader objective of hitting a target dew point; the moisture analyzer is the instrument that measures the result. When the analyzer trends toward the limit, operators can act on the actual cause, such as a lean glycol that has picked up too much water, a low circulation rate, a saturated desiccant bed due for regeneration, or a temperature that has drifted, rather than discovering the problem only when a downstream custody meter or a pipeline flags off-spec gas.
Because wet gas causes real damage, hydrate plugs that block lines, internal corrosion, and freeze-offs, a continuous moisture reading is a safeguard as much as a quality check. It gives early warning of a dehydration upset and documents that the facility is delivering gas within the pipeline's water specification.
A moisture analyzer produces a live water-content reading, typically as a 4-20 mA output or a digital value, and often additional status and alarm outputs for validity and maintenance. That reading is wired into the site PLC, RTU, or flow computer as a gas-quality tag alongside the flow, pressure, and temperature measurements at the dehydration and custody points.
A cloud SCADA platform such as Merobix reads that moisture tag over Modbus, DNP3, or OPC UA, so operators can trend gas moisture continuously, set an alarm before the reading reaches the pipeline limit, and view dehydration performance across many sites from a browser. On remote and unmanned gas sites this is especially valuable, because a dehydration upset that pushes gas off-spec would otherwise go unseen until a periodic sample or a pipeline complaint. A remote high-moisture alarm lets a small team catch a failing glycol unit or a spent desiccant bed and dispatch before off-spec gas is delivered.
Trending the moisture signal against the dehydration equipment's own variables, such as glycol circulation, reboiler temperature, or regeneration cycle timing, also helps operators tie a rising moisture reading to its cause. Watching that relationship over time turns the analyzer from a pass-fail gate into an early-warning tool that flags a drying problem while there is still time to correct it.
Water content in natural gas is usually reported as pounds of water per million standard cubic feet, written lb/MMscf, which is a concentration. It can also be expressed as a water dew point, the temperature at which water would begin to condense out of the gas at operating pressure, where a lower dew point means drier gas. Pipelines typically set a maximum water content or dew point that incoming gas must meet.
A glycol dehydration unit is the equipment that removes water from the gas, while a moisture analyzer is the instrument that measures how much water remains after drying. The dehydration unit does the work; the analyzer is the independent check that confirms the gas has been dried below the pipeline's water specification. A rising analyzer reading warns that the dehydration process is failing before the off-spec gas reaches a custody point.
Water in gas causes hydrates that can plug lines, internal corrosion of pipelines and equipment, and freeze-offs in cold conditions, all of which threaten reliable delivery. To prevent this, pipelines set a strict moisture limit that gas must meet before it can enter, so every facility has to dry its gas and prove it stays within spec. A continuous moisture analyzer both verifies compliance and gives early warning of a dehydration upset.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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