What Corrosive Media Are PTFE Differential Pressure Transmitters Suitable For?

During production processes in chemical processing, environmental protection, electroplating, hydrometallurgy, pharmaceuticals, fine chemicals, and other industries, pressure or level measurement of acid solutions, alkaline solutions, salt solutions, and chlorine-containing media is often associated with significant corrosion risks. Conventional stainless-steel wetted parts may develop pitting corrosion, crevice corrosion, stress corrosion cracking, and other issues after long-term contact with corrosive media, thereby affecting the zero stability, measurement accuracy, and service life of differential pressure transmitters.

A PTFE differential pressure transmitter generally refers to a differential pressure measuring device in which the diaphragm, lining, sealing components, or pressure-guiding structure in contact with the medium is made of PTFE material, or which adopts a PTFE protective structure. PTFE offers excellent chemical stability, low surface energy, and good corrosion resistance, helping equipment cope with a variety of highly corrosive operating conditions.

However, PTFE does not mean that it is suitable for all media. During actual selection, factors such as medium concentration, temperature, pressure, the presence of solid particles, crystallization tendency, vacuum conditions, diaphragm seal construction, and flange material should also be comprehensively confirmed to avoid making a judgment based solely on the single factor of “corrosion resistance.”

I. Corrosion Resistance Characteristics of PTFE Wetted Structures

1. Chemical Stability Suitable for Various Corrosive Liquids

PTFE has a stable molecular structure and good resistance to many common inorganic acids, organic acids, strong alkalis, and salt solutions. Under ambient or low-to-medium temperature conditions, PTFE wetted diaphragms can reduce the likelihood of direct contact between the medium and metal diaphragms, making them suitable for differential pressure, level, and filter differential pressure monitoring in corrosive media.

For acidic media such as hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid, the actual medium concentration and operating temperature should be carefully verified. For example, dilute acid at ambient temperature and concentrated acid at high temperature have different corrosion mechanisms. Selection should not be based only on the name of the medium, but also on process parameters and material compatibility data.

Under alkaline solution conditions involving sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and similar substances, PTFE generally exhibits good chemical inertness. For applications such as alkali solution tank level measurement, scrubber differential pressure measurement, and filtration differential pressure in alkali solution circulation pipelines, corrosion-resistant diaphragm seals can reduce direct exposure of the sensor to the medium.

PTFE also features a low coefficient of friction and low adhesion. For certain corrosive media that are prone to buildup, crystallization, or slight stickiness, the proper selection of flush diaphragms, flush mounting, or remote seal structures helps reduce pressure tap blockage and measurement drift.

2. Differential Pressure Measurement Structures Cannot Be Evaluated by Diaphragm Material Alone

A differential pressure transmitter consists of a sensing element, isolation diaphragm, fill fluid, process connection, sealing gasket, impulse piping, and electrical structure. Even if the diaphragm surface uses a PTFE protective layer, insufficient corrosion resistance of the flange, bolts, capillary tube, impulse line, or sealing ring may still cause overall failure.

For equipment installed directly on vessel flanges, the medium resistance of the flange material, wetted spool, gasket, and fasteners should be confirmed at the same time. For remote differential pressure measurement structures, the outer protection material of the capillary tube, fill fluid temperature range, and installation environment must also be confirmed to prevent transmission errors caused by high or low temperatures.

When the medium has strong oxidizing properties, strong permeability, or high-temperature characteristics, PTFE structures may face risks of permeation, deformation, aging, or seal failure. For such operating conditions, it is recommended that technical personnel conduct an overall assessment based on process pressure, temperature fluctuations, installation location, and maintenance intervals.

Xi'an Shenghongchuang Instrumentation Co., Ltd. can provide differential pressure transmitter selection support based on specific media, measurement ranges, flange specifications, output signals, and installation methods, and can configure suitable wetted materials and diaphragm seal solutions according to actual operating conditions.

II. Common Applicable Corrosive Media and Application Scenarios

1. Differential Pressure Monitoring of Acidic Media

PTFE differential pressure transmitters are commonly used in measurement systems for hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, citric acid, and certain mixed-acid solutions. In acid pickling, electroplating, waste acid recovery, exhaust gas absorption, chemical cleaning, and acid solution transfer processes, they can be used to monitor tank levels, reactor differential pressure, filter blockage levels, or pressure differentials upstream and downstream of pumps.

For example, in a hydrochloric acid scrubber, the transmitter can reflect changes in tower resistance through the pressure difference between the high- and low-pressure sides. When packing becomes clogged, spray volume is abnormal, or gas-liquid contact conditions change, the differential pressure signal can provide reference for process adjustment and equipment maintenance.

The suitability for sulfuric acid media must be evaluated in combination with concentration and temperature. Material compatibility may differ for low-concentration sulfuric acid, high-temperature sulfuric acid, and sulfuric acid containing impurities. In particular, liquid accumulation, dead zones, or crevices should be avoided at equipment connection points to reduce the risk of localized corrosion and crystal deposition.

For hydrofluoric acid, mixed acids, or high-purity acid applications, it is recommended to provide complete medium composition information before purchase, including acid type, concentration range, maximum temperature, normal pressure, and cleaning cycle. Clearly defining these parameters can reduce downtime and maintenance costs caused by material selection deviations.

2. Alkaline Media and Salt Solution Applications

In caustic soda preparation, alkaline washing, papermaking, printing and dyeing, wastewater neutralization, and chemical cleaning systems, sodium hydroxide solution is relatively common. PTFE wetted structures can generally be used for differential pressure measurement of such alkaline media, but attention should be paid to the effects of high-temperature concentrated alkali on other materials, sealing components, and fill fluids in the system.

Salt solutions such as sodium chloride, calcium chloride, sodium sulfate, copper sulfate, and ferric chloride are widely used in industrial production. Salt solutions themselves may be electrically conductive and may crystallize due to concentration, evaporation, or temperature reduction. Therefore, measurement locations should avoid areas prone to deposits whenever possible.

In electroplating solutions, acid pickling wastewater, and saline wastewater treatment, the medium composition is generally complex and may simultaneously contain acids, alkalis, heavy metal ions, chloride ions, and suspended solids. In this case, in addition to considering PTFE corrosion resistance, attention should also be given to scale buildup on the diaphragm surface, solid abrasion, and blockage of pressure-sensing passages.

For differential pressure measurement upstream and downstream of filtration equipment, the measuring range may be selected according to the filter's normal resistance and allowable pressure drop. A certain margin is commonly reserved. For example, when the normal differential pressure is 20 kPa to 40 kPa, a range of 60 kPa, 100 kPa, or another more suitable differential pressure range can be selected in consideration of system fluctuations, avoiding long-term full-scale operation.

3. Chlorine-Containing, Oxidizing, and Exhaust Gas Scrubbing Media

Chlorine-containing media are common in sodium hypochlorite preparation, bleaching, disinfection, water treatment, electroplating exhaust gas treatment, and auxiliary chlor-alkali chemical systems. Chloride ions can easily cause pitting corrosion and crevice corrosion in certain metal materials, so wetted material selection should be more cautious.

For oxidizing media such as sodium hypochlorite, chlorine-containing wastewater, and bleaching solutions, in addition to confirming the compatibility of PTFE layers or PTFE sealing components, concentration, pH value, temperature, and the presence of free chlorine should also be confirmed. In actual processes, medium fluctuations are often more significant than nominal formulations, and selection should refer to the highest-risk operating conditions.

In acid mist absorption towers, alkali scrubbers, and exhaust gas treatment equipment, differential pressure transmitters are commonly used to monitor packing layer resistance. A continuous increase in differential pressure may indicate packing scale buildup, uneven spraying, mist eliminator blockage, or abnormal gas flow, facilitating timely inspection by maintenance personnel.

For moist chlorine gas, mixed acid mist, or corrosive gas-liquid two-phase media, particular attention should be paid to preventing condensate from entering pressure-guiding sections that are not corrosion-resistant. Priority should be given to appropriate pressure tapping structures, diaphragm seal methods, and installation slopes to improve long-term measurement stability.

III. Reference Table for Medium Compatibility

The above table is a preliminary reference for common operating conditions and does not replace material compatibility confirmation for specific projects. Especially for mixed media, recovered liquids, mother liquors, waste liquids, and process liquids with frequently changing formulations, complete chemical composition and the most stringent operating parameters should be used as the basis for selection.

Medium temperature is an important variable affecting material performance. Even the same corrosive liquid may have significantly different effects on diaphragms, sealing components, and fill fluids at 20°C, 80°C, and 150°C. In actual projects, normal temperature, maximum temperature, and short-term abnormal temperature should all be provided.

Process pressure and differential pressure range should also be confirmed separately. System static pressure may reach 1.0 MPa, 1.6 MPa, or even higher, while the actual differential pressure to be measured may be only 10 kPa to 50 kPa. Only by properly matching the static pressure rating and differential pressure range can measurement resolution and equipment reliability both be ensured.

For corrosive liquid tank level measurement using the differential pressure method, medium density must also be considered. Liquid level height, density changes, and tank pressure can all affect differential pressure conversion results. Where necessary, temperature compensation, density correction, or a more suitable level measurement solution should be configured.

IV. Special Media for Which Direct Use of PTFE Solutions Is Not Recommended

1. Caution Required for Strong Fluorinating Media, Active Metals, and Extreme Operating Conditions

Although PTFE has a broad corrosion resistance range, it is not suitable for all chemical media. Alkali metals in molten or high-temperature states, certain strongly fluorinating media, and special reaction media may adversely affect PTFE and cannot be selected simply based on conventional acid and alkali resistance experience.

For special media such as liquid or gaseous fluorine and strongly oxidizing fluorides, dedicated confirmation should be carried out based on professional material compatibility data and actual process conditions. Such conditions generally also involve safety ratings, sealing methods, leakage risks, and protection requirements, and require joint evaluation by process, equipment, and instrumentation personnel.

Systems with high temperatures, high vacuum, or frequent pressure pulsations may also pose significant challenges to PTFE linings or PTFE sealing structures. Materials may experience cold flow, creep, or changes in seal preload under temperature cycling and mechanical stress; therefore, installation methods and maintenance intervals must not be overlooked.

If the medium contains large amounts of hard particles, crystals, or high-velocity slurry, the PTFE surface may also be subject to abrasion. For applications involving mineral slurry, crystallized salt slurry, or sand-containing wastewater, flow velocity, particle size, and solids content should be considered to determine whether an abrasion-resistant structure or a change in pressure tapping location is required.

2. Key Parameters Recommended Before Selection

To ensure the compatibility of a PTFE differential pressure transmitter, it is recommended to clearly specify the medium name, complete composition, concentration range, pH value, density, viscosity, and whether it contains solid particles. For mixed liquids, the main components and possible by-products should be listed instead of providing only the process abbreviation.

Temperature parameters should include normal operating temperature, maximum temperature, minimum temperature, and frequency of temperature changes; pressure parameters should include system operating pressure, maximum allowable pressure, differential pressure range, and possible pressure shocks. The more complete the parameters, the more conducive they are to determining the configuration of the diaphragm, flange, sealing components, and fill fluid.

Installation information is equally important, including pipe diameter, flange standard, pressure tap location, equipment orientation, whether vibration is present, and whether the site is located in a hazardous area. For different equipment such as filters, towers, and storage tanks, differential pressure tapping methods and impulse piping structures also differ.

Regarding signal configuration, 4 mA to 20 mA, RS485 communication, or other suitable methods can be selected according to the requirements of the control system. For applications requiring interlock protection, alarm thresholds, display requirements, power supply conditions, and the on-site cable routing environment should also be confirmed.

V. PTFE Differential Pressure Transmitter Selection Comparison Table

PTFE differential pressure transmitters are suitable for measurement requirements involving various acidic, alkaline, salt, and chlorine-containing corrosive media. Especially in applications where conventional metal wetted materials are unable to operate stably over the long term, they can provide a reliable instrument configuration option for filter differential pressure, tower resistance, tank level, and pipeline differential pressure monitoring.

However, the core of corrosion-resistant measurement is not merely selecting PTFE material, but achieving systematic matching of the medium, temperature, pressure, connection type, sealing structure, and installation location. For complex corrosive operating conditions, sufficient preliminary technical confirmation can reduce the risks of subsequent leakage, drift, blockage, and frequent maintenance.

Xi'an Shenghongchuang Instrumentation Co., Ltd. and its production base, Shaanxi Qinkong Sensor Technology Co., Ltd., provide differential pressure transmitters, pressure transmitters, level transmitters, and supporting intelligent instrumentation products for industrial automation measurement and control requirements, and can provide non-standard customization and technical services based on on-site operating conditions.

To determine whether a PTFE differential pressure transmitter is suitable for your acid solution, alkaline solution, chlorine-containing solution, or mixed corrosive medium, please provide information on medium composition, concentration, temperature, static pressure, differential pressure range, and installation interface in order to obtain selection recommendations better suited to on-site operating conditions.