Caspian Petroleum Terminal Case: Crude Oil Tank Level Gauging With 26 GHz Explosion-Proof Radar

Crude oil storage tanks ask one level measurement to do two jobs: inventory, and overfill protection. This case study presents a decision analysis for a crude tank at a tank farm, where the medium has a low dielectric constant (typically around 2-4, depending on water cut and temperature) and sits under a hydrocarbon vapor space in a classified hazardous area. The measurement is difficult because the echo from a low-dielectric surface is weak, emulsion and foam can cover the surface after filling, and heated crude creates vapor and mist. The previous servo level gauge failed mechanically and required frequent maintenance, while manual dipping could not provide continuous data and exposed operators to VOC emissions. Three replacement options are compared - servo rebuild, guided wave radar and non-contact 26 GHz pulse radar - and the article explains why the third won, how it was configured, and what changed for the operators.

Client Profile: Caspian Petroleum Terminal LLP (Atyrau, Kazakhstan)

Caspian Petroleum Terminal LLP operates a crude oil storage and transshipment terminal in Atyrau, Kazakhstan, receiving crude from field pipelines and dispatching it by rail and export route. The terminal's tank farm runs a mix of fixed-roof and internal floating-roof tanks, and its operations team depends on dependable level data for both inventory reconciliation and overfill protection.

2. The Duty: One Measurement, Two Jobs

The crude tank has to do two things with one level reading. For inventory, the level is converted to volume through the tank's strapping table and reconciled with receipts and dispatches - a slow, forgiving duty. For overfill protection, the same level feeds a high-high alarm that must be dependable every hour of every day - a fast, unforgiving duty. The tank is large-diameter and atmospheric, with a hydrocarbon vapor space above the crude and a classified hazardous area on the roof. Heavy crude may be heated, so the vapor space can be warm and misty. The level changes slowly except at the start and stop of filling, which means the measurement does not need speed - it needs stability, availability and trust.

3. The Physics Problem: A Weak Echo From a Low-Dielectric Surface

Crude oil reflects only a small fraction of an incident radar wave because its dielectric constant is only about 2-4. The echo is weak, and anything that disturbs the surface - emulsion, foam, waves from filling - weakens or shifts it further. In a heated tank, vapor and mist sit between the antenna and the surface. The instrument therefore needs enough transmitted energy, an appropriate frequency and antenna, and a signal-processing strategy that can distinguish the true surface echo from noise. The same physics explains why some technologies never worked well here: anything relying on acoustic reflection (ultrasonic) or on contact with the surface (servo floats) fights the same environment with worse tools.

4. Why the Servo Gauge Kept Breaking

The servo gauge lowered a displacement float on a measuring wire until the wire tension changed at the surface. The principle is sound; the mechanism is not. The wire drum, motor and encoder are mechanical parts that wear, the float sticks in waxy or emulsion-covered crude, and every fault meant climbing the tank and often opening the gauge hatch - exactly the exposure the site wanted to avoid. Calibration drifted between visits, and the reading was only as good as the last maintenance intervention. Manual dipping remained the fallback: accurate as a snapshot, but intermittent, VOC-exposing, and unable to feed a continuous alarm loop. The site needed an electronic measurement with nothing inside the tank except the sensing element itself.

5. Three Options on the Table

The project team compared three paths, and the comparison is worth reproducing because it shows the reasoning:

Non-contact radar won because it eliminated the failure modes at the root: no moving parts, no internal probe to damage, no maintenance access inside the tank.

Recommended Qinwei Instruments for This Application

7. Why 26 GHz Pulse Won Over 80 GHz

The frequency decision is where engineering judgment shows. An 80 GHz radar offers a narrower beam and better resolution, but in this service two arguments favored 26 GHz. First, the lower frequency is attenuated less by vapor and mist - relevant in heated or humid tanks. Second, on a large-diameter tank the wider beam of 26 GHz is not a disadvantage: it averages the surface over a larger footprint, which actually stabilizes the reading on a wavy or tilted crude surface. The 26 GHz pulse technology also has a long, documented record in tank-farm gauging, which matters when the measurement feeds custody-adjacent inventory. Explosion-proof certification is non-negotiable on the tank top, so an Ex-rated housing was specified. Where the tank has a stilling well, a PTFE drop-in antenna is used. Inside a stilling well the signal propagates within a metal pipe, which concentrates the beam and shields it from surface waves; a PTFE drop-in is used because a bare metal horn inside the well would create a secondary reflection at the pipe wall.

8. The Configuration: From Antenna to Strapping Table

The radar was configured for level referenced to the tank bottom: tank height and nozzle offset entered, 4-20 mA scaled over the working range, HART enabled for remote diagnostics and re-ranging. Because crude is a low-dielectric medium, the echo threshold was set for low-dielectric liquids - a setting that must not be copied from a water-tank installation. The threshold has to be low enough to catch the weak crude echo but high enough to reject noise; that balance is a commissioning judgment, not a default. The high-high alarm was set below the tank rim per the site's overfill procedure, and the fail-safe direction was set so that a lost echo drives the output toward the alarm state. Volume conversion from level was done in the tank gauging system using the strapping table, not in the transmitter - the transmitter measures distance; the system turns it into barrels.

9. Roof Work: Installation and Safety

Installation on a tank roof is governed by the hazardous area before it is governed by the measurement. The instrument was mounted on the existing roof nozzle with the antenna below the nozzle bottom; on the internal floating-roof tank, the mounting was coordinated with the floating roof travel and the roof leg area. The antenna was kept away from the fill inlet. Surge protection was fitted at the tank base - on a tall steel structure in open ground, lightning-induced surges are a real reliability factor, not an accessory. The cable run to the junction box was mechanically protected, and all work followed the site's hot-work and confined-space permits.

10. Commissioning Against the Dip Tape

Commissioning started with an empty-tank echo survey so the transmitter learned the fixed echoes from the nozzle, roof structure and internal fittings; false-echo suppression was applied to those targets. Tank height, offset, scaling and alarm thresholds were entered, and the fail-safe direction was tested by disconnecting the loop. The radar reading was then compared with a manual dip at several levels. On crude oil, agreement within approximately +/-5 to +/-10 mm is realistic depending on surface condition, and the actual deviations were recorded. The HART tag and address were set to match the tank gauging database, and the volume conversion was verified against the strapping table before the tank was returned to service.

Why Choose Qinwei Instruments

Xi'an Qinwei Instrument Factory (brand QINWEIYB) is a manufacturer established in 2010 that specializes in industrial automation instruments, with 500-800 employees and 50%-60% of output exported worldwide. For tank-farm service, Qinwei supplies explosion-proof radar level gauges with 4-20 mA and HART output, self-cleaning antenna options for waxy crude, and configuration support for strapping-table integration. All instruments are factory-calibrated with traceable certificates; MOQ starts from 1 set, delivery is 5-8 working days, and OEM/ODM customization is supported.

12. What Changed for the Operators

The operators noticed the change in their routines before they noticed the display. The servo gauge's mechanical failures stopped because there were no moving parts. Manual dipping became a scheduled verification instead of a routine necessity, cutting VOC exposure. The high-high alarm was backed by a continuous measurement instead of a snapshot. The control room gained a level signal that the tank gauging system, the DCS and the alarm logic all used consistently. Site-specific figures are not provided; the operational result was that the measurement became continuously available and the tank no longer required mechanical attention.

13. Value in Tank-Farm Terms, and Where the Pattern Repeats

For a tank farm, the value shows up as safety (a continuous, explosion-proof measurement with a tested fail-safe direction), operations (better scheduling of receipts and dispatches, fewer roof climbs, no servo maintenance cycle), and data quality (HART diagnostics and echo curves let the instrument engineer verify the measurement remotely). The same configuration applies to crude, fuel oil, diesel and gasoline in atmospheric storage, and to refinery feed and product tanks. For pressurized or liquefied-gas storage the selection logic changes - different antenna, different certification, possibly guided wave - and should be evaluated separately. When requesting a quotation for tank-farm radar, provide the tank type and height, roof nozzle size, product and its typical temperature, water cut if variable, and the area classification - these decide the frequency, antenna and Ex rating.