Can an IP68 Differential Pressure Sensor Be Submerged in Water Long-Term? First Distinguish Between “Waterproofing” and “Reliable Long-Term Operation

IP68 differential pressure sensors typically offer a high level of dustproof and waterproof protection. When the specified immersion depth, duration, and test conditions are met, they can be used in humid, water-accumulated, short-term, or long-term submerged environments. However, “IP68” does not mean the sensor can operate stably without limit in any water quality, at any depth, or under any installation method. Actual use should still be assessed comprehensively based on the sensor structure and site conditions.

For differential pressure measurement products, protection concerns involve not only the housing, but also the pressure connections on the high-pressure and low-pressure sides, impulse lines, cable outlets, venting structures, and connectors. If any one of these parts is exposed for a long period to water pressure, corrosive media, or mechanical pulling, moisture may enter through weak points, resulting in zero drift, signal fluctuation, reduced insulation, or even internal circuit failure.

Therefore, whether an IP68 differential pressure sensor can be used long-term in a submerged environment depends not simply on the protection rating shown on the label, but on confirming the test conditions corresponding to that rating and verifying the measured medium, external immersion medium, installation depth, temperature variation, and maintenance cycle. For applications such as clean water, tank level differential measurement, and pump station filter differential pressure, long operating periods can generally be achieved with proper selection and standardized installation.

If the site involves wastewater, seawater, acid or alkali solutions, oily waste liquids, or high-salt-spray environments, the wetted materials, chemical resistance of sealing components, and corrosion resistance of the cable sheath need further evaluation. Even if short-term waterproofing is satisfactory under such conditions, long-term service life cannot be determined based on IP68 alone.

Understanding IP68: The Practical Limits of the Protection Rating

What Do “6” and “8” in IP68 Mean?

The IP protection rating consists of two digits. The first digit, “6,” indicates a high level of dust protection, preventing dust from entering the enclosure and affecting normal operation. The second digit, “8,” indicates that the device can be continuously submerged under conditions specified by the manufacturer. Compared with IP67, IP68 is generally intended for greater water depths or longer immersion periods, but the specific depth and duration are not universally fixed values.

For example, some products are specified for continuous immersion at a depth of 1 m for 24 hours, while others can operate long-term at depths of 3 m, 5 m, or even deeper. For every additional 10 m of water depth, the external hydrostatic pressure increases by approximately 0.1 MPa. Therefore, as the sensor installation depth increases, the external pressure borne by the housing, cable, and sealing sections also increases accordingly.

It should be noted that IP68 testing primarily verifies the protection capability of the external enclosure. It is not directly equivalent to the process pressure, static pressure overload, or differential pressure overload that the measurement end can withstand. For differential pressure sensors, parameters including measuring range, one-sided overpressure, two-sided static pressure, and burst pressure must also be confirmed separately to avoid excessive impact during pipeline start-up and shutdown or valve switching.

During procurement or selection, it is recommended to require the supplier to clearly specify the immersion depth, immersion duration, test medium, test temperature, and installation requirements corresponding to IP68. Only when these conditions are close to the actual site conditions does the protection rating have practical reference value.

Four Key Factors Affecting Long-Term Submerged Service Life

Reliability of the Sealing Structure and Pressure Connections

Differential pressure sensors generally have two pressure inlets, and both the high-pressure and low-pressure sides must remain sealed. For threaded connections, the thread specification, sealing gasket, sealing tape, and tightening torque should all be properly matched. When connected through impulse lines, pipe fittings, valve manifolds, three-valve manifolds, and venting and draining points are also potential leakage points.

Under long-term immersion, external water pressure continuously acts on cable sealing ends and connection areas. For products installed underwater, structures such as integral potting, laser welding, and directly sealed cable outlets are more suitable, minimizing the long-term direct immersion of standard plug-in circular connectors.

During on-site assembly, external components must not be overlooked simply because the sensor body meets IP68. A junction box with a lower protection rating or an inadequately tightened cable gland can become the starting point of water ingress and failure for the entire measurement system.

For locations requiring disassembly and maintenance, installation above the liquid level should be prioritized. Where underwater installation is unavoidable, watertight connectors rated for the required water depth should be used, and pressure-holding or insulation checks should be performed before commissioning.

Corrosiveness of External Water Quality and Wetted Media

Clean water has relatively little effect on stainless steel housings and standard sealing components, but domestic sewage, industrial wastewater, seawater, and chlorine-containing media significantly increase corrosion risk. In particular, seawater or high-chloride-ion environments may cause pitting corrosion and crevice corrosion in ordinary metal parts, weakening the integrity of sealing surfaces after long-term operation.

If the measured medium itself is acid, alkali, solvent, or high-temperature liquid, the “external immersion medium” and the “internal measured medium” should be evaluated separately. The sensor diaphragm, pressure connections, and sealing rings contact the process medium, while the housing, cable, and connection parts may simultaneously contact external liquid. The material requirements on the two sides may not be the same.

Common 316L stainless steel is suitable for various industrial water media, but it is not suitable for all highly corrosive applications. For high-concentration acids or alkalis, high-salinity, high-temperature, or sulfide-containing conditions, more suitable diaphragm materials, sealing materials, or remote diaphragm seal configurations should be selected according to the medium concentration, temperature, and pressure.

The more complete the medium information, the more reliable the selection conclusion. At a minimum, the medium name, concentration range, temperature range, maximum operating pressure, presence of solid particles, and whether periodic cleaning or disinfection processes are involved should be provided.

Temperature Cycling and Condensation Must Not Be Overlooked

Long-term submerged equipment does not operate only in still water at ambient temperature. Day-night temperature differences, hot-water flushing, equipment start-up and shutdown, and seasonal changes can cause repeated thermal expansion and contraction of the housing and sealing materials. As the number of temperature cycles increases, issues such as compression set of sealing rings and aging of bonding layers may gradually occur.

When there is a temperature difference between the inside and outside of the sensor, a small amount of moisture may also condense internally. For products with vented compensation designs, the vent must be protected from direct immersion or blockage by contaminants; otherwise, pressure balance and measurement stability may be affected.

In applications with significant temperature fluctuations, models whose specified operating temperature range covers the site conditions should be prioritized, with an appropriate temperature margin retained. For example, if the maximum on-site water temperature is close to 80°C, selection should not be made only at the critical upper limit of 80°C.

For high-temperature immersion, alternating hot and cold conditions, or outdoor freeze-thaw environments, simulated operating-condition validation is recommended before installation. Periodic calibration, visual inspection, and insulation testing should also be included in the maintenance plan.

Selection and Installation Recommendations for Different Submerged Applications

Differential pressure sensors are commonly used in pump stations, filtration equipment, and circulating water systems to monitor filter blockage, pipeline resistance, or liquid level differential pressure. In these applications, particular attention should be paid to matching the measuring range to the actual differential pressure. The normal operating differential pressure should fall within a reasonable portion of the range, while pressure margin should be reserved for pump start-up, water hammer, and filter blockage.

For locations prone to flooding, such as tanks, underground wells, and outdoor equipment pits, sensors should preferably be installed in positions convenient for inspection, with pressure routed through properly installed impulse lines to an instrument installation point above the liquid level. Where it is necessary to place the entire instrument underwater, installation depth, mounting method, and cable routing should be designed as a complete solution.

Differential pressure impulse lines should avoid air pockets, trapped liquid, or deposition dead zones that are difficult to drain. When measuring liquid differential pressure, impulse lines generally need to maintain a continuous downward slope; when measuring gas differential pressure, condensate must be prevented from entering the sensing element. Incorrect installation orientation may result in measurement errors, and reliable data cannot be obtained even if the sensor’s waterproof performance is normal.

For signal output, 4-20mA two-wire systems are widely used in industrial applications and provide relatively stable anti-interference and long-distance transmission performance. When using digital communication such as RS485, shielding, grounding, termination resistors, and waterproofing of communication lines must also be properly addressed. Supply voltage, load capacity, and cable length should also be calculated according to the manual.

Maintenance Methods to Extend the Submerged Service Life of IP68 Differential Pressure Sensors

For long-term submerged applications, it is recommended to establish a regular inspection system. During routine checks, observe whether the output is stable, whether the zero point has shifted abnormally, whether the housing shows signs of corrosion, and whether the cable jacket has hardened, cracked, or suffered external abrasion. If irregular signal fluctuations are found, the sealing of wiring terminals and the condition of impulse lines should be checked first.

For wastewater, slurry, or particle-containing liquids, cleaning of pressure ports and piping should be arranged according to the degree of contamination. During cleaning, avoid direct contact between sharp metal objects and the sensitive diaphragm. High-pressure water jets exceeding the product’s specified pressure should also not be aimed at pressure connections, to prevent diaphragm damage or contamination of the measurement chamber.

Periodic verification is recommended in combination with critical process requirements. Under general conditions, verification can typically be scheduled every 6 to 12 months. Where the system has high differential pressure control accuracy requirements, or where strong corrosion, frequent pressure shocks, or temperature cycling are present, the inspection interval should be appropriately shortened, and the zero point, full-scale output, and insulation condition should be recorded.

Xi’an Shenghongchuang Instrumentation Co., Ltd. can match suitable IP68 differential pressure sensors and supporting installation solutions for projects based on actual water depth, medium composition, differential pressure range, static pressure, temperature, output signal, and installation method. After on-site operating parameters are provided, material selection, sealing structure, range margin, and long-term immersion reliability requirements can be further confirmed.