Steam Jacketed Oval Gear Flowmeter for Bitumen and Asphalt Loading

For terminals and mixing plants where bitumen arrives at 175 °C and sets solid the moment the heat is lost. The jacket surrounds the chamber on all sides, so the measuring chamber stays above the pour point during loading, between tankers and through a winter night.

Steam jacketed oval gear flowmeter, DN100 body with steam jacket and Ex d enclosure.

Second view: jacketed end cover with steam ports, drain and vent plugs.

Why an Unheated Meter Fails on Bitumen Within Weeks

Bitumen is not a difficult fluid, it is a fluid that changes state. Penetration grade 60/70 has a viscosity around 300–600 cP at 175 °C and effectively stops flowing below about 110 °C. Any meter with cold spots — a bare end cover, an unjacketed flange face, a support boss — accumulates solid product in that cold spot. On the next batch the pump builds pressure against a plugged chamber, and the price of that pressure is a sheared rotor pin or a cracked cover.

The second failure mode is silent. A partially blocked chamber still passes product, so the register still counts, but the displaced volume no longer matches the geometry. Custody transfer figures drift, customers dispute loaded quantities, and the correction is found only after a proving run.

There is also a compliance dimension. Bitumen terminals are usually classified hazardous areas, so the instrument must carry explosion protection, and the batch record must survive an audit. A meter that has to be dismantled every few weeks for cleaning satisfies none of those requirements in practice.

Two Working Conditions, Measured Side by Side

How the Jacketed Chamber Keeps Product Moving

Two oval rotors mesh inside a chamber and carry a fixed volume from inlet to outlet on each rotation, driven by the product pressure alone. That much is common to every oval gear meter: the same principle appears in the twin rotor flowmeter and the rotary piston flowmeter, each suited to a different balance of viscosity and volume. What is specific here is where the heat comes from: the steam jacket wraps the body and both end covers, and the flange faces are insulated with jacketed spacers, so heat reaches the measuring chamber from all directions rather than from one side.

The result is that the rotor faces, the meshing line and the chamber wall stay within a few degrees of each other. Uniform wall temperature is what preserves the rotor clearance: if one cover runs 30 °C cooler, differential expansion pinches the rotor at that end, and the meter either stalls or wears its gear faces rapidly.

Because the measurement counts trapped volume, viscosity only sets the pressure required. Raising viscosity from 500 cP to 3,500 cP increases differential pressure and slows the rotor — it does not change the volume carried per revolution, so the K factor established at 175 °C holds for the whole range of grades you load.

Structural Features for 250 °C, Thermal Cycling and Hazardous Areas

Thermal duty is a materials question more than a measurement question. The design choices that matter:

• Jacket on body and both covers, rated 0.6 MPa saturated steam. No unheated surface is in contact with product, so there is no cold spot for bitumen to set in.
• Media rating to 250 °C with thermal cycling tolerance. Graphite or PTFE-graphite packing and cover gaskets selected for repeated heat-up and cool-down rather than a single steady state.
• Explosion protection to Ex d IIB T4. Flameproof terminal enclosure and a certified cable entry suitable for Zone 1 gantry installations.
• Drain and vent tappings on both covers. The chamber can be emptied while still warm, which is the difference between a routine stop and a rotor replacement.
• Mechanical register plus electronic outputs. A local counter for the driver at the gantry, and pulse, 4–20 mA and RS485 Modbus RTU for the batch controller and custody record.

Six Advantages on a Bitumen Terminal

Sizing and Installation for Loading Arms and Batch Blending

Size on the highest loading rate, because the constraint on bitumen is pressure drop, not resolution. A DN100 chamber covers roughly 20–60 m³/h at 300–600 cP while keeping differential pressure low enough for a centrifugal loading pump; for modified grades at 2,000 cP and above, go one size larger and run slower rather than raising pump pressure.

Start steam tracing with line pre-heat, not after the tanker connects. A cold DN80 unit needs 45–60 minutes to reach temperature with 0.6 MPa saturated steam; keeping the jacket warm between batches is gentler on seals than repeated cold starts. Mount the meter in a vertical line with downward flow where possible, or horizontally with the drain plug at the lowest point, and interlock jacket steam pressure or jacket temperature with the batch controller so loading cannot start on a cold meter. Tank inventory that matches the loading record is normally taken from radar level gauges on the storage tanks.

For custody transfer, agree the proving method before installation: a prover loop or a calibrated tank check, repeated quarterly, with a K factor correction entered in the controller if deviation exceeds 0.2%. We supply the correction formula and a dimensional drawing marked with drain, vent and jacket connection positions so the piping can be built correctly the first time.

Tanker loading gantry layout (schematic drawing): pre-heat the meter with the line before the tanker connects.

Application Case 1: Bitumen Terminal Loading Gantry, UAE

Application Case 2: Modified Asphalt Plant, Kazakhstan

Technical Specifications

Frequently Asked Questions

How long does the jacket take to heat a cold meter before loading?

Allow 45 to 60 minutes with 0.6 MPa saturated steam on a DN80 unit starting from ambient, and around 90 minutes for DN150 with heavy flanges. The jacket surrounds the body and both end covers, so heat reaches the measuring chamber from all sides rather than one face, which is what keeps the rotor clearance from pinching as the metal expands. In practice plants start steam tracing with the line pre-heat, before the first tanker connects, so the meter is already at temperature when product arrives. If you load continuously, keep steam on the jacket between batches rather than cycling it — repeated cold starts stress the gaskets far more than warm standby does.

Can it handle SBS modified bitumen at high viscosity?

Yes, up to about 4,000 cP at 160–180 °C, which covers most polymer-modified grades in commercial use. The gear pair is driven by the product itself, so higher viscosity raises differential pressure rather than changing the measured volume, and the reading stays inside 0.5% as long as the pump can hold the required differential. Two requirements apply for modified binder: keep jacket steam pressure steady so viscosity does not swing mid-batch, and stay above the minimum flow so the rotors do not stall. For heavily filled or fibre-reinforced bitumen we recommend a larger size running at lower speed, which reduces shear and wear on the rotor faces.

What happens if the steam supply fails during loading?

The meter keeps measuring, but product cools in the chamber within minutes and viscosity climbs steeply below 120 °C, so differential pressure rises and flow falls. Stop loading, drain the chamber through the bottom plug while it is still warm, and restore steam before resuming. Never leave cold bitumen sitting in a measuring chamber: on restart, differential pressure across solidified product can shear a rotor pin or crack a cover. A simple interlock on jacket temperature or steam pressure, wired to the batch controller, prevents the situation completely and costs far less than the repair. Our drawings mark the drain and vent tapping positions you need to make that routine practical.

How is the meter verified in the field without removing it?

Use a prover loop or a calibrated tank and totaliser check. Run a known mass or volume of product through the meter at normal loading rate, compare the register reading with the reference, and record the deviation. Because the meter produces a pulse output, the check takes minutes and can be done between tankers, which is how most terminals handle their quarterly custody transfer procedure. If deviation exceeds 0.2%, a K factor correction can be entered in the batch controller; we supply the correction formula with the certificate. Only if mechanical wear is suspected — normally after abrasive service — does the unit need to come off the line for bench recalibration.

Related Products and Further Reading

Bitumen terminals usually need measurement and inventory on the same page, so these are the most requested links:

• Positive displacement flowmeters — the complete range, including unjacketed versions for lower-temperature oil service.
• Twin rotor flowmeter — non-contact rotors with low pressure loss for large pipeline volumes.
• Rotary piston positive displacement flowmeter — high range ratio for chemical and refinery duties.
• Radar level gauges — tank inventory to match the loading figures the flowmeter produces.
• Float flowmeters — small purge and seal-flush flows around the loading pump.

Tell us the grade, the loading rate and the steam pressure available on site, and we will specify the jacket and the size in one reply.