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Orifice meter units with differential pressure transmitters remain the most practical flow restriction solution for saturated and superheated steam lines. Silver Instruments supplies complete orifice plate assemblies, 3-valve and 5-valve manifolds, impulse line accessories, and 4-20 mA HART DP transmitters for line sizes from DN25 to DN900. Tell us your steam pressure in bar, temperature in °C, pipe size in DN, and flow range in kg/h and our engineers will return a quote for a standardized orifice meter unit within one working day.
Steam duty is hard on flow meters. High temperature, thermal shock during startup, and wet steam during low load all limit meter choices. An orifice plate has no moving parts and no electronics in the pipe. That makes it easier to repair on site than a vortex meter or a thermal mass meter.
A refinery in Thailand runs a saturated steam header at 12 barg and 188 °C. They replaced two inline flow meters with a single orifice meter unit and a DP transmitter. Maintenance downtime dropped because the only wetted part is a 316 SS plate. A paint manufacturer in Vietnam asked us to size a DN150 orifice meter unit for a superheated steam line at 16 barg and 240 °C. The plate needed a beta ratio of 0.52 to keep the DP across the transmitter span from 25 mbar to 500 mbar.
Most engineers skip the detailed theory. What matters is that ISO 5167 and ASME MFC-3M define the geometry, tolerances, and installation requirements. A properly machined orifice plate with a beta ratio between 0.3 and 0.7 gives repeatability better than 0.1 percent of installed span. In practice, total system uncertainty in steam service depends on the DP transmitter, the pressure and temperature compensation, and the impulse line condition.
Silver Instruments offers orifice meter units as complete kits, not loose plates. A standard kit for a DN100 steam line includes a 304 SS or 316 SS orifice plate, a wafer or flanged carrier, a 3-valve manifold, two condensate pots, two 316 SS impulse valves, and a differential pressure transmitter with 4-20 mA HART output. We also supply the pressure transmitter and PT100 RTD for density compensation. The flow computer or paperless recorder can display mass flow in kg/h, totalized flow in kg, and live temperature and pressure.
For corrosive steam or offshore marine applications, we quote Hastelloy C276 and Monel 400 plates. Line sizes range from DN25 to DN900. Pressure ratings for flanged assemblies can be supplied from PN16 up to PN420 or ASME Class 150 through 2500. A customer in Singapore ordered four DN150 orifice meter units for a new steam distribution header at 21 barg and 320 °C. The DP transmitters were ATEX Zone 1 rated and the manifolds used 316 SS bodies with PTFE packing.
DP hardware selection starts with the differential pressure range. For steam, we size the plate so that the normal operating flow produces a differential between 10 and 90 percent of transmitter span. Common spans are 0 to 250 mbar, 0 to 500 mbar, and 0 to 2.5 bar for high velocity steam. The transmitter accuracy should be no worse than 0.075 percent of span for boiler efficiency tests. For ordinary process control, 0.1 percent of span is enough.
3-valve manifolds are standard for most steam lines. 5-valve manifolds are specified when the transmitter needs to be isolated for in-place calibration without shutting down the steam header. We have seen many installations where a missing condensate pot caused unstable DP readings at low flow. Condensate pots keep the impulse lines full of liquid water at a constant height on both sides of the plate.
Installation mistakes cause most orifice meter errors. Impulse lines should slope downward from the taps to the transmitter or condensate pots at a minimum of 1:10. For horizontal steam lines, the taps should be located on the side or top of the pipe so the impulse lines stay liquid filled. The upstream straight run is usually 20D to 30D depending on the beta ratio and the fittings before the meter. If the steam line has a control valve, a strainer, or a bend within 10D upstream, the specified accuracy will not hold.
Here is the thing: on steam lines, using a flow computer with live pressure and temperature compensation matters more than the plate itself. Because saturated steam density changes sharply with pressure, a pressure error of 0.5 bar at 10 barg can add a density error near 3 percent. We configure the compensation formula in our paperless recorders and flow computers according to IAPWS IF-97 or SGERG-88, depending on the plant standard.
Typical steam metering applications include boiler main steam headers, district heating supply lines, turbine inlet steam, sterilizer and autoclave lines, and steam injection for food processing. A dairy in New Zealand measures saturated steam at 7 barg for pasteurization and cleaning in place. They use a DN50 orifice meter unit with a HART DP transmitter and a paperless recorder. Flow range is 800 to 5000 kg/h. The recorder stores the last 730 days of steam flow data. For condensate return lines, a conductivity sensor from Silver Instruments can monitor carryover in µS/cm and feed the same paperless recorder.
Oil and gas sites in the Middle East often need sour gas or offshore marine ratings. We quote orifice plate carriers in duplex stainless steel and fasteners in B7M or B8M. For steam lines with intermittent flow, a standard DP transmitter may not read correctly below 1 percent of flow. In these cases we add a low flow cut off in the flow computer and upgrade the transmitter to a digital HART model with square root output.
To request a price for an orifice meter unit for steam, send us these five values: pipe size in DN, steam pressure in bar, steam temperature in °C, flow range in kg/h, and pipe schedule or wall thickness. Include the transmitter protocol if known. We quote 4-20 mA HART as standard. For hazardous areas we quote ATEX Zone 1 or Zone 2 and IECEx versions. A complete quote covers the plate, carrier, manifold, condensate pots, DP transmitter, PT100, pressure transmitter, and flow computer or paperless recorder if required.
What pipe sizes can Silver Instruments supply for steam orifice meter units?
We supply line sizes from DN25 to DN900. Plates can be wafer, flanged, or RTJ type for high pressure steam headers.
Can an orifice meter measure wet steam?
It can measure wet steam only if you add pressure and temperature compensation and accept higher uncertainty. Wet steam quality below 95 percent changes density calculation. In practice, a separator or steam trap upstream is required for stable measurement.
Which DP transmitter output is standard on your steam orifice meter units?
4-20 mA HART with square root output is standard. Foundation Fieldbus and Profibus PA are available on request. The transmitter can be supplied with ATEX Zone 1 or IECEx certification.
How long does delivery take for a standardized orifice meter unit?
Standard DN50 to DN300 wafer assemblies with 316 SS plates take 5 to 8 working days. Flanged assemblies and exotic alloys typically take 12 to 20 working days depending on the pressure rating and material.
Do you supply spare orifice plates for existing meter bodies?
Yes. Send the existing plate thickness, outer diameter, bore diameter, tap type, and material. We machine a replacement plate to ISO 5167 or ASME MFC-3M and ship it with a surface finish certificate.
For steam orifice meter quotes, contact Silver Instruments. Our sales engineers answer during Asia business hours and can provide dimensional drawings with the quotation.
Tel: +86-25-68650347
Whatsapp: +86-25-52155837
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Website: flow-meter.com.au
