Choosing the technology for a chemical metering skid starts with three questions: is the liquid electrically conductive, does the sale or the process need mass or volume, and is density or concentration also required? The answers narrow down the meter type. The wetted material is then selected from the meter manufacturer's compatibility data for the product's real concentration, temperature and impurities, not simply matched to the piping. The skid brings the meter, isolation, strainer, pressure and temperature measurement and control elements together on one pre-assembled frame.
First split: is the liquid conductive?
Magnetic (electromagnetic) flowmeters measure the voltage induced as a conductive liquid moves through a magnetic field. They have no moving parts, a full-bore flow path with low pressure loss, and are widely considered for aqueous acids, caustics and salt solutions. The principle does, however, require the liquid to exceed a minimum conductivity. That minimum is not a universal constant: manufacturer datasheets give different values even for different sizes within one product line. Many organic solvents and hydrocarbons fall below it and cannot be measured magnetically.
Coriolis mass flowmeters do not depend on conductivity and measure mass flow directly. The same device also reports density and fluid temperature, so volume can be calculated and concentration derived for two-component solutions. That multivariable capability makes Coriolis a frequent choice at mixed-product chemical terminals, but the thin vibrating tubes make material selection more critical.
Technology | Strength in chemical service | Limiting condition |
Magnetic flowmeter | No moving parts, low pressure loss, adaptable to corrosive aqueous solutions through liner and electrode options | Minimum conductivity requirement; measures volume, so mass needs a separate density value |
Coriolis flowmeter | Direct mass, density and temperature; independent of conductivity; suited to concentration calculation | Localized corrosion and fatigue risk in thin tubes; entrained gas and deposits can disturb readings |
Positive displacement meter | Volume measurement of viscous, non-conductive clean liquids | Moving parts and tight clearances; limited with abrasive or solids-laden products |
Turbine meter | Volume measurement of clean, low-viscosity products | Sensitive to viscosity changes; bearing material must suit the product |
Wetted materials: do not copy the piping spec
The most common mistake in chemical metering is specifying the meter's wetted material to match the line piping. A Coriolis manufacturer's corrosion guide explains why that is not enough: piping selection usually ignores cyclic loading, while meter tubes vibrate continuously. Tests based on general (uniform) corrosion rates do not reveal localized corrosion such as pitting, intergranular attack, stress corrosion cracking or corrosion fatigue, and on a vibrating tube localized corrosion can initiate fatigue cracks.
The same guide stresses that small changes in temperature, concentration or impurity level can change compatibility and that material selection is ultimately the user's responsibility. The sequence is therefore: define the actual product specification, review the manufacturer's compatibility data for that product and condition, and consult the manufacturer or test where data is missing or marginal. Materials offered for Coriolis meters include stainless steel grades, super duplex, nickel alloys, titanium and tantalum; which one fits depends entirely on the product.
In magnetic flowmeters, the product-contacting surfaces are the liner and electrodes. The liner is assessed for temperature and chemical resistance, the electrodes for corrosion and for any coating tendency that could affect the measurement signal. Here, too, the choice rests on product-specific manufacturer data.
Gaskets and connections
Even with a suitable meter body, the flange gaskets, strainer cover O-ring, valve seals and transmitter process connections on the skid are each checked. When several products pass through one skid, seals are selected for the most aggressive of them. Fewer flanges mean fewer potential leak points, and drip trays or collection are provided beneath those that remain. Sealing and leak collection for corrosive products are covered on the corrosive fluid transfer page.
Density and concentration
The density and temperature measured by a Coriolis meter allow concentration to be calculated in a two-component solution, provided the relationship between density, temperature and concentration for the carrier fluid and target component is known. Manufacturer documentation recommends fitting that calculation only over the actual application window, since a wider window means more linearization and lower accuracy. A third component, dissolved gas or temperatures outside the range will distort the result. Inline concentration therefore supports continuous monitoring and control rather than replacing laboratory analysis.
Process and dosing measurement
Many metering skids in chemical plants serve process needs such as reactor feed, blend ratio or tank-to-tank transfer rather than custody transfer. Repeatability, turndown and a fast signal to the control system may matter most here. On low-flow dosing lines, meter size is checked so the flow does not sit at the bottom of the measuring range. Ratio injection of additives and transfers that need a precise cutoff at a target quantity are covered on their own pages.
Cleaning between products
If one skid will handle several products, it is designed to drain from the outset. Meter position and orientation are chosen so product does not remain in the tubes, dead legs are avoided, and drains are placed at low points and vents at high points. The flushing medium is a chemical too: it must not react with the product and must be compatible with the meter and seal materials. The changeover procedure defines how flush liquid left in the meter affects the first quantity of the next product.
Design criteria
Parameter | Why it matters in design | Impact on selection |
Conductivity | Decides whether the magnetic principle applies | Magnetic or conductivity-independent technology |
Concentration, temperature and impurities | Change material compatibility and localized corrosion risk | Tube, liner, electrode and seal materials |
Viscosity and solids content | Affect meter performance and wear | Technology and strainer selection |
Risk of gas or bubbles | Can disturb both flow and density readings | Back pressure, gas separation, mounting orientation |
Purpose of measurement | Process, dosing and custody transfer carry different requirements | Verification method, records and sealing |
Number of products | Shared skids complicate cleaning and seal selection | Drainable layout, flushing connections |
Hazardous area and environment | Sets the protection method for electrical equipment with flammable products | Transmitter and panel selection |
Working with TLY Enerji
On chemical metering skid projects, TLY Enerji can help evaluate process data to choose between magnetic, Coriolis and other flowmeter technologies, supply meters and instruments, integrate data into PLC or SCADA systems, and support site installation and commissioning. Which manufacturer compatibility data will govern the wetted material decision, and who gives final material approval, are agreed at the start of the project.
What we need to define your skid
· Product name, full concentration range, temperature range and known impurities
· Conductivity value, or whether the product is aqueous or organic based
· Minimum, normal and maximum flow, plus the lowest flow on dosing lines
· Purpose: process control, dosing, tank-to-tank transfer or custody transfer
· Whether a density or concentration output is needed
· Number of products through the skid and changeover frequency
· Existing line material, connection standard and hazardous area class
Related pages
· Chemical custody transfer metering systems: Turning a measured quantity into a basis for sale.
· Corrosive fluid transfer systems: Pump, liner and leak collection decisions for acids and caustics.
· Batch metering systems for chemicals: Recipe-based target quantities and cutoff management.
· Additive injection at chemical terminals: Ratio dosing and dose verification.
Common questions on chemical metering
Which chemicals can a magnetic flowmeter not measure?
Liquids that fall below the meter's minimum conductivity requirement, which includes many organic solvents, hydrocarbons and some high-purity liquids. Because the minimum conductivity varies by manufacturer, model and even meter size, borderline products should be checked against the specific datasheet, or a conductivity-independent technology such as Coriolis should be considered instead.
Can the meter material simply match the pipe material?
Not always. Piping selection usually does not account for cyclic loading, whereas Coriolis tubes vibrate continuously and localized corrosion can start fatigue cracks. Manufacturer corrosion guides state that meter material cannot be inferred from the piping alloy. The choice should rest on the meter manufacturer's compatibility data for the product's actual concentration and temperature.
Can a Coriolis meter measure chemical concentration?
For two-component solutions, yes, provided the relationship between concentration, density and temperature is known. The calculation is reliable only within the defined application window; a third component, dissolved gas or out-of-range temperature will distort it. Inline concentration is therefore mainly used for continuous monitoring and control, while laboratory analysis remains the basis for quality acceptance.
Can one metering skid serve different chemicals?
Yes, if the products are compatible with each other and with the skid materials, the skid is designed to drain and changeovers follow a defined procedure. Seals are chosen for the most demanding product, and the flushing medium is checked for compatibility as well. Incompatible products are better served by separate skids or at least separate meter runs.