On a heated metering skid, a cold spot forms wherever heat loss outpaces heat input. Preventing them comes down to three things: putting every component on the skid onto a heating circuit, designing insulation in sections that can be opened for maintenance without losing continuity, and controlling heat by measuring product temperature. A heating scheme that works on straight pipe can fall short on a skid, where meter bodies, strainer covers, valve actuators, instrument connections and drains form a dense row of thermal bridges.
Choosing a tracing method for pipelines is covered on the heat tracing page, and the effect of viscosity on meter technology on the heavy oil metering skid page. This page is about how heating is arranged at skid scale and how heating control influences the measurement result.
Where cold spots hide on a skid
A metering skid packs many heavy, irregular components into a short length of pipe, so cold-spot risk is more concentrated than on a line and has to be handled component by component.
· Meter body and electronics neck: The massive meter body is slow to warm, while the electronics sit outside the insulation to stay cool, leaving a thermal bridge in between.
· Strainer and air eliminator: Covers, baskets and drain connections expose large surfaces and cool fastest; they are also what gets opened most often.
· Valve bodies and actuators: Control and isolation valve bodies need heating, while actuators and positioners must stay within their permitted ambient temperature.
· Instrument connections: Pressure transmitter impulse lines, protruding thermowells and sample points have small cross-sections and block most easily.
· Proving connections and bypass: These branches see flow only during proving and sit stagnant in normal operation, where product can solidify.
· Skid inlet and outlet flanges: The boundary between line heating and skid heating is the point most often forgotten when responsibilities are split.
Heating method: electric tracing or jackets?
Heating methods at skid scale (qualitative comparison)
Method | Strength on a skid | What to watch |
Electric heat tracing | Adapts to irregular surfaces and small connections; each circuit can be measured and monitored | In hazardous areas the IEC/IEEE 60079-30 series applies; maximum sheath temperature is checked against product and area classification |
Steam or thermal oil tracing | High heat input where a heating medium is available on site | Condensate removal and return lines take up skid space; running a separate branch to every component complicates the layout |
Meter or valve heating jacket | Surrounds a heavy component and keeps its temperature even; for some Coriolis meters manufacturers offer two half-shell jackets | Jacket and heating-medium pressure and temperature limits are assessed together with the meter electronics' ambient limit |
Jacketed pipe | Full or partial jacketing gives high, uniform heat input | Reduces connection and maintenance flexibility on a skid; more common for products handled at very high temperature |
In practice most skids combine methods: the meter body jacketed, strainers and valves traced or fitted with heating pads, and small instrument connections served by thin cables. What matters is that every component's circuit, and what that circuit measures for control, are clearly defined.
How heating control affects the measurement
On a heated skid, temperature governs not only flowability but the measurement itself. If temperature drops below setpoint, viscosity rises: pressure drop worsens on a positive displacement meter, and on a Coriolis meter both pressure drop and low-flow performance suffer. If the setpoint is higher than necessary, density falls, the same mass occupies more volume, and electronics move closer to their ambient limits. The setpoint is therefore derived not from the pour point but from the product's viscosity–temperature data and the viscosity range allowed by the meter and pump.
Sensor location matters as well. A sensor close to the heater surface switches heating off early while the product is still cold. The sensor measuring product temperature should be separate from any sensor limiting heater surface temperature, and the temperature measurement used for volume correction should be independent of heating control and close to the meter. Temperature differences from uneven heating around the meter can influence the zero of some meter types, so meter zeroing is carried out once the skid has reached operating temperature and stabilized.
Balancing insulation and maintenance access
On a skid, insulation continuity and maintenance access are in constant tension: strainers need cleaning, meters need proving, valves need replacing. Permanent insulation that is hard to remove gets damaged at every intervention and goes back incomplete, which over time means new cold spots. Removable insulation covers on frequently opened components, shaped jackets for flanges and valves, and labeled connection points are therefore preferred. Heating circuits are also split so that removing one component does not require de-energizing the whole skid.
Cold start, shutdown and monitoring
A heated skid has to be designed for the weakest moments of operation. On a cold start the skid is heated before the pump, and the pump should not run until product temperature reaches setpoint. During long shutdowns heating is either kept on or the skid is drained; the right choice depends on the product, the length of the stop and energy cost. Wiring low- and high-temperature alarms, circuit faults and pump start permissives into PLC or SCADA prevents a cooled skid from being started unnoticed.
Hazardous areas and standards
Where explosive atmospheres may occur, general and testing requirements for electrical resistance trace heating fall under Part 1 of the IEC/IEEE 60079-30 series; IEC/IEEE 62395-1 covers the same subject for non-hazardous industrial areas. Which requirements apply depends on the site's hazardous area classification and the project specification. If several heating methods are used on one skid, the temperature class and control method of each are assessed separately.
TLY Enerji's role
For heated metering skids, TLY Enerji provides engineering support covering the selection and supply of measurement technology and instruments, installation and commissioning of meters and sensors, and monitoring heating-circuit temperatures and alarms through PLC or SCADA. Who supplies the heat tracing system itself, and where line heating ends and skid heating begins, are settled at project start.
Information needed to design a heated skid
· Product viscosity–temperature data and the target metering temperature range
· Minimum ambient temperature, wind exposure, and outdoor or indoor installation
· Heating media available on site (steam, thermal oil) and electrical infrastructure
· Hazardous area classification
· Component list on the skid and maintenance frequency of each
· Cold-start and extended-shutdown scenarios, and whether the skid can be drained
Related pages
· Heat tracing for heavy oil and fuel oil lines: Choosing a tracing method along the line.
· Bitumen metering skids: Metering with jacketed meters at higher temperatures.
· Heavy oil metering skids: How viscosity shapes meter technology.
· Fuel oil metering skids: Skid layout for consumption and transfer metering.
· Heated transfer systems for pyrolysis oil: A product where heating is capped by thermal stability.
Heated metering skid FAQ
Should the meter electronics be heated too?
No. The electronics are not heated; they are protected from excessive heat. While the meter body is heated, the electronics must stay within the manufacturer's permitted ambient temperature. Where insulation needs to extend toward the electronics, extended-neck or remote-mounted electronics options are considered.
How is the heating setpoint determined?
The setpoint follows from the product's viscosity–temperature data, the viscosity range allowed by the meter and pump, and how well the product tolerates high temperature. Pour point is only a lower-limit index. A setpoint higher than necessary wastes energy, lowers density and pushes electronics toward their temperature limits.
Can skid heating and line heating be one system?
They can, but the skid usually needs its own circuits, because component heat losses and maintenance frequency differ from pipe sections. What matters is a clear boundary: which circuit the skid inlet and outlet flanges belong to, and whose scope of supply they fall under, should be written down at project start.
During a long shutdown, should the skid be drained or kept heated?
Both approaches are used. For short, predictable stops, keeping heat on is usually more practical. For long stops, draining saves energy but requires a sloped, fully drainable skid design and a preheating period before restart.
When should a meter on a heated skid be zeroed?
After the skid has reached operating temperature and the meter body and product temperature have equalized. Zeroing during warm-up can build temperature differences into the meter adjustment. Zeroing conditions and the temperature at the time should be recorded.