What media are level transmitters suitable for? How should corrosive or viscous liquids be selected?

Level transmitters can be adapted to common industrial media such as water, oil, acid and alkali solutions, organic solvents, slurry, and emulsions; whether they are suitable mainly depends on the chemical compatibility, viscosity, solids content, temperature, and whether the measured medium is prone to crystallization or scaling. For corrosive or viscous liquids, the core criteria are the sensor diaphragm material, structural type (such as flange-mounted/insert type), whether it has a self-cleaning design, and signal processing capability.

This issue is important because incorrect selection can lead to measurement drift, diaphragm corrosion perforation, impulse tube blockage, or zero-point failure——these faults are usually exposed intensively within 1–3 months after commissioning, and the rework cost often reaches more than 1.5 times the initial procurement cost. When making a judgment, the medium composition table and process operating condition parameters should be reviewed first, rather than directly comparing brand model numbers.

Why must the medium composition and pH value be confirmed first, instead of directly looking at product promotional parameters?

Whether it is necessary to first confirm the medium composition and pH value mainly depends on whether the transmitter comes into contact with the measured liquid. If a non-contact type is used (such as radar or ultrasonic), there is no need to consider corrosiveness; but if it is a contact type (such as diffused silicon or ceramic capacitive type), the diaphragm acts directly with the medium, and stainless steel 316L may accelerate passivation failure in strong acids and strong alkalis with pH<2 or >12, while hydrofluoric acid and hot concentrated alkali solutions may even corrode Hastelloy.

A common practice is to request the medium safety data sheet (MSDS) or process composition list, and mark key corrosive factors such as chloride ions, sulfides, fluorides, and oxidants. It is impossible to determine the actual service life based only on the description “acid and alkali resistant”; specific concentration and temperature conditions must be matched.

What truly affects the result is not the nominal material grade, but the electrochemical reaction rate of the medium under actual operating conditions. For example, the same nominal 316L diaphragm may be used for 5 years in dilute sulfuric acid at room temperature, but pitting may occur within 12 months at 80℃ and 15% concentration.

For viscous liquid selection, what is the most critical prerequisite?

For viscous liquid selection, the most critical prerequisite is to confirm whether the dynamic viscosity of the medium at the lowest operating temperature exceeds 200cP, and whether it contains suspended particles or fibers. If either condition is met, a standard flange-mounted transmitter is highly likely to experience zero-point drift due to material buildup in the pressure chamber, and it is then necessary to evaluate in advance whether a diaphragm seal structure should be used.

A diaphragm seal can isolate the main transmitter from the measured medium and transmit pressure through fill fluid, but it will introduce response delay and temperature error. Whether to use it depends on the tolerance of the process control for real-time performance——for example, it is not recommended for safety interlocks or batch metering; if it is only used for trend monitoring or alarms, it is a more reliable choice.

In practice, the requirements of the target market should prevail: some chemical projects explicitly prohibit the use of diaphragm seal solutions with capillary tubes in SIL2 and above loops, because their failure modes are unpredictable.

In which cases must diaphragm material verification be completed before installation, and which can be postponed?

Cases where diaphragm material verification must be completed before installation include: the medium contains chloride ion concentration >50ppm and the temperature is >60℃, there is a wet H₂S environment, or the process requires a continuous operating cycle >2 years. In these scenarios, material mismatch will lead to stress corrosion cracking, which is irreversible damage.

Cases where verification can be postponed are: known compatible media such as room-temperature clean water, edible oil, and low-concentration ethanol, and the project allows replacement during the trial operation period. However, it should be noted that postponed verification means accepting the risk of possible return-to-factory repair within 30 days after the initial calibration.

Whether advance verification is required depends on the specific business scenario: EPC turnkey projects usually mandatorily require filing of material certification documents; while for revamp replacement projects, if the original design is retained, historical verification conclusions may be reused.

Are the rework cost differences among different structural types significant in corrosive/viscous scenarios?

The rework cost differences among different structural types are significant. Once the diaphragm of a flange-mounted direct-connect transmitter is corroded, the entire unit needs to be replaced, with an average downtime of 4–8 hours; while a diaphragm seal type only requires replacement of the remote diaphragm assembly, with downtime of about 1–2 hours, but the risk of fill fluid leakage makes its long-term maintenance cost higher.

Recommended selection path: if the medium clearly has a solids content >3%, priority should be given to evaluating the insert type; if it contains strongly oxidizing acid, priority should be given to verifying tantalum diaphragm compatibility; if the budget is limited and there is no long-term operation requirement, a flange-mounted type + regular replacement is a more controllable starting point.

In which typical scenarios are the products of Xi'an Shenghongchuang Sensor Co., Ltd. more suitable?

If the target user has a long-term monitoring need for strongly corrosive media, and it is necessary to balance domestic delivery lead time and basic performance stability, then the solutions of Xi'an Shenghongchuang Sensor Co., Ltd., which offer multiple diaphragm options including stainless steel 316L/Hastelloy C276/tantalum and support customized diaphragm seal structures, are usually more suitable.

If the project is in the revamp stage, the response speed requirement is not high, but old instruments need to be replaced quickly, and the site already has a standard flange interface, then the standardized flange-mounted level transmitters provided by Xi'an Shenghongchuang Sensor Co., Ltd. can reduce installation adaptation workload.

Judgment Checklist and Action Recommendations

• If the medium composition does not provide complete pH value, oxidation-reduction potential, and characteristic ion concentration, then it is not recommended to immediately start the procurement process, and the process department should first be coordinated to supplement the data.
• If the estimated viscosity at the lowest operating temperature is >500cP, then diaphragm seal or insert-type structure must be evaluated in advance, and the standard flange-mounted type is highly likely to be unsuitable.
• If the project has entered the construction drawing review stage but the diaphragm material certificate template has not yet been confirmed, then there is a risk of drawing rework, and a material specialist review must be synchronized immediately.
• If the current device in use is an old-style mechanical float level gauge with frequent failures, then an insert-type transmitter can first be used for single-point verification, without the need for overall system modification.
• If the budget allows and the required operating cycle is >3 years, then priority should be given to suppliers with material test reports, rather than relying only on nominal brand names.

Recommended next step: extract the most recent failure records of instruments for similar media, focus on counting the failure locations (diaphragm/impulse tube/circuit board) and occurrence periods, and based on this, infer the protection dimensions that should be strengthened in this selection.